Jika anda ternampak muka saya tengah TT (Teh Tarik) ni, bermakna anda telah selamat mengharungi 3 hari bumi tak jadi bergelap, dan tarikh 21hb Dis yang penuh tragis dan huru-hara (kononlah).

:-D

Nak ceritanya, Falak Online telah pun berpindah rumah. Bermula sekarang silalah kemaskini link ke WWW.FALAKONLINE.NET ,  tak perlulah letak apa-apa selepas tu, kerana ia akan redirect ke muka hadapan BARU yang sepatutnya.

Laman lama (yang anda lihat sekarang ni), InsyaAllah akan kekal untuk beberapa bulan mendatang. Ia akan menyenaraikan KESEMUA artikel lama saya di FO, bagi rujukan anda semua. Maka, kalau anda nak masih nak marah-marah kat saya berkenaan artikel "3 hari bergelap tu" , masih boleh berbuat demikian, saya terima dengan hati terbuka! :-)

Apa pun, InsyaAllah 2013 mendatang akan terdapat beberapa pembaharuan yang saya dan rakan-rakan Personaliti Astronomi lain usahakan, demi kemajuan bidang Astronomi di Malaysia.

Jom dan Selamat Datang Ke Tahun Baru 2013. 

Jemput masuk --->  WWW.FALAKONLINE.NET

 

Astronomy

Tips for Shooting Great Nightscapes

Sky and Telescope - Mon, 10/08/2015 - 21:00

Capturing the Earth and sky in one great composition is surprisingly easy.
By Babak A. Tafreshi in the Sky & Telescope November 2012 issue

Shooting the splendors of the night sky above storybook landscapes, such as this scene in Iran’s Alborz Mountains, is a relatively easy way to get started in astrophotography. What appears to be a river of glowing red water is actually a person walking with a red flashlight and pointing it toward the ground.
Babak A. Tafreshi

Seen from a little island off the coast of Brazil, the Milky Way hangs above coconut palms. Gentle waves break the island silence, softly washing the shore’s tiny grains of sand. Millions of those grains are under my feet as I stand next to my camera, trying to capture both the boundless cosmic ocean above and the quiet terrestrial one below.

This attempt to capture the beauty of the Earth and sky is known as landscape astrophotography. The resulting nightscapes made using off-the-shelf cameras and lenses are immensely successful in astronomy outreach. Picturesque terrestrial landmarks crowned with the stars above allow viewers to relate to otherwise abstract celestial sights. These wide-field photos often reveal surprising astronomical and atmospheric phenomena impossible to record through a telescope’s narrow field of view. We often think of the universe as an astronomer’s laboratory, but these celestial portraits remind us that the night sky is also an essential part of nature — and therefore of us.

Striking this balance between art and science in nightscapes is one of the more challenging aspects of landscape astrophotography, but if done properly, these images can revitalize the sublime experience of naked-eye observing.

Right Place, Right Time

Today’s nightscape astrophotographers are pursuing the hobby at the right time. When I began photographing the night sky in the early 1990s, photography was a complex and fickle endeavor. My first successful sky image came after months of trial and error with a single-lens reflex camera. I had to figure out the best films and exposures, as well as find a reliable photo lab. Today, thanks to digital technology, delicate Earth and sky images appear on my camera’s LCD screen as soon as the exposure is complete.

Compared with telescopic astrophotography, nightscape imaging is a low-gear endeavor; you don’t need a vast array of high-tech equipment. A single camera, tripod, and a shutter-release cable will not only get you started, they are almost all you need as a nightscape astrophotographer. Post-processing of your images is also minimal, because you’re aiming to create an image resembling what an observer might see with the unaided eye.

In nightscape astrophotography, unexpected occurrences can often enhance a composition. Broken clouds add to the beauty of this photo of Venus over Dasht-e Kavir in central Iran.
Babak A. Tafreshi

Keeping your equipment as compact as possible also helps you tackle the real challenge of landscape astrophotography — getting to the right location at the right time. Much of your setup time will involve traveling to remote locations, searching for picturesque landscapes, and waiting for the right moment. Unless you’re particularly fortunate, you’ll never take the best nightscapes in your backyard. The view down your street with electricity wires, streetlights, and other signs of urban life will often degrade an otherwise wonderful nightscape. Being at the right place at the right time usually comes with careful planning, which includes knowledge of the night sky.

Having the minimal amount of equipment not only helps you move around during the night to find the best compositions, it also allows you to enjoy your time under the starry sky. My usual imaging gear consists of two cameras: one used to capture still images that I move to different positions throughout the night, and another to record time-lapse sequences. Everything fits conveniently inside a backpack.

When shooting nightscapes from remote locations such as this site in the Semnan Desert in northeastern Iran, it’s best not to go alone, and to always let someone know where you’re going. But don’t take too many people along on an imaging trip, either.
Babak A. Tafreshi

Also consider the size of your team. I tend to avoid doing night photo sessions when I’m alone, and I always let someone know where I’m going when I shoot from a remote location. On the other hand, larger groups cause their own issues, including too many tripods to trip over and sometimes too many flashlights in my photos. Astrophotography in small teams of two or three people is often the most comfortable

Choosing Your Gear

The most important tool for taking world-class nightscapes is obviously your camera. Although some great twilight photos can be taken with pocket digital cameras, serious landscape astrophotography is impractical with compact digital cameras. Their average nighttime sensitivity is mediocre at best. The newest point-and-shoot cameras use small detectors boasting a dozen megapixels or more, which may sound wonderful at first. But these detectors incorporate extremely small pixels that aren’t well suited for nightscapes, as I’ll explain in a moment. Additionally, compact point-and-shoot cameras come with a single zoom lens, which more often than not is both photographically slow and often has poor edge quality that reveals itself as distorted stars near the corners of the image.

The best choice for nightscape photography is a digital single-lens-reflex camera (DSLR). These cameras feature dozens of advantages over point-and-shoot cameras, including high sensitivity, interchangeable lenses, manual exposure and aperture settings, bulb exposure mode (which enables practically unlimited exposure lengths), and a RAW file mode that preserves the dynamic range of your image (June issue, page 68). Most recent DSLR models utilize “live view,” which provides on-screen focusing and can display the brightest stars at night, greatly simplifying the process of achieving proper focus.

Babak A. Tafreshi

DSLRs are very sensitive to light, much more so than even the best films of the past. And while you can adjust the ISO setting to achieve “faster” performance than point-and-shoot cameras, the latest models offer much lower noise at the same ISO settings than cameras manufactured just a few years ago. Changing the ISO setting of your camera doesn’t truly increase its sensitivity to light, but rather electronically amplifies the signal readout from your camera’s CMOS detector. This amplification has the cost of producing more noise in the image.

When shooting a brilliant aurora, it’s easy to point the camera up and snap away. Don’t forget to include some foreground to help give your audience some visual cues to the scale of the display. This composition from northern Sweden includes a small cabin that helps to connect the viewer with the events in the scene.
Babak A. Tafreshi

A DSLR’s true sensitivity depends on a number of factors, such as the sensor’s quantum efficiency, or QE. This is the percentage of usefully recorded photons compared to the total that strikes the detector. The QE of a human eye ranges from 1 to 5%. A rough estimate for the peak QE of current DSLR cameras ranges from 30 to 40%. Note that the QE changes across the spectrum and thus depends on the wavelength of the light striking the detector. A camera’s QE also varies in each of the RGB color filters incorporated in the camera’s Bayer matrix.

Under a dark, moonless sky, current DSLRs perform well at ISO 1600. This is a good compromise between photographic speed and noise in the resulting images. A goal in nightscape astrophotography is to capture a sharp landscape and pinpoint stars. You can often avoid tracking if you limit your exposure to roughly 30 seconds with a 15-millimeter lens, or up to a minute with very wide-angle or fisheye lenses. Beyond that, the stars will trail noticeably. Some new camera mounts, such as Vixen’s Polarie (reviewed in the March issue, page 58), compromise between the stars and foreground image by tracking at half the normal rate. This speed allows you to shoot longer exposures before stars become objectionably long trails while also not contributing much blur to the foreground.

Slower ISOs of 200 to 800 work well at twilight, in bright moonlight, or in considerable light pollution, and when shooting star trails. Slower ISOs record fewer stars and won’t capture fainter objects such as the Milky Way in short exposures of the sky, but they have the benefit of lower noise, better dynamic range, and they produce more saturated star colors.

The Multi-Megapixel Lure

Another important factor that determines a camera’s sensitivity is the size of the individual pixels in the camera’s sensor. These tiny, photon-collecting wells are like buckets collecting raindrops. The larger a pixel is, the more photons it can collect before it gets full, or saturated. Although new cameras that boast small pixels provide higher resolution and capture sharper details (particularly in telescopic planetary imaging), they lack the sensitivity of sensors with larger pixels, and the small pixels quickly saturate during long exposures. Rapid saturation results in colorless white stars across the field and low dynamic range when using high ISOs.

Another consideration when choosing a camera for nightscape astrophotography is determining if you want a full-frame sensor or one of the smaller APS-format cameras. A full-frame sensor requires lenses that can illuminate the whole detector. This is an important consideration, because most camera manufacturers offer lenses specifically for their APS cameras, and these will seriously vignette the corners of the full-frame camera.

While some of the best choices for nightscape photography are full-frame cameras such as the Canon 5D Mark II and the Nikon D3, they aren’t absolutely necessary. Under a dark sky and using a good wide-angle lens, you can make a 30-second exposure at ISO 1600 on most current APS-format cameras and still record a surprisingly glorious view of the Milky Way. When choosing an APS-format DSLR for nighttime imaging, remember to avoid budget models with high megapixel counts, because their super-sharp daytime performance won’t last when the Sun sets.

Lenses as Your Telescopes

Even the best DSLR cameras produce mediocre images when coupled with a cheap lens. Consider investing in high-quality lenses with fixed focal lengths. Zoom lenses are often inadequate for any kind of low-light photography. The wide-range zoom lenses such as the standard 18-to-200-mm zoom that comes with many camera packages offer you both wide views of constellations and close-up Moon shots. But these complex lenses use many optical elements and offer slow photographic f/ratios that limit how deep you can go in short, untracked exposures.

The basic lens for nightscape photography is a wide-angle lens ranging from roughly 15 to 35 mm for full-frame cameras, ideally f/2.8 or faster. An APS-format camera lens equivalent would range from 10 to 24 mm. These fast, fixed-focal-length lenses are the key to success in low-light photography. With a fast 15-mm f/2.8 lens, a 30-second exposure at ISO 1600 will reveal faint nebulae and star clusters within the Milky Way.

When shooting with lenses faster than f/2.8, stop the aperture down one or two f/stops to achieve the sharpest focus and to reduce coma at the corners. For example, a good 24-mm f/1.4 lens should be stopped down to at least f/2 to produce good star images across the entire image.

For close-up views of celestial events such as conjunctions or eclipses, a telephoto lens in the range of 85 to 200 mm is required. Longer, fast telephoto lenses (500 mm and more) are quite expensive, and small apochromatic refractors with similar focal lengths are usually much better optically and less costly.

Cities can also offer a great setting for wonderful nightscapes. Here the author calculated where to set up in Paris to catch the setting Moon next to the famous Arc de Triomphe using a long telephoto lens.

Shooting Old School

Finally, what about film cameras? Film nightscape astrophotography is still alive (see images by The World at Night photographer Oshin Zakarian at www.twanight.org/zakarian). Film cameras are very affordable and still a perfect supplement to your digital equipment. Available films today are relatively slow but work fine for imaging at twilight, under bright moonlight, and for long-exposure startrails. Film cameras with manual shutters don’t require electricity to function in bulb mode. Medium-format film cameras are available on the used market often at bargain prices and produce wonderful nightscape photographs. You can still find medium-format films of ISO 800 in many professional photo stores, or online.

These tips should get you well on your way to capturing wonderful scenes of conjunctions, meteor showers, and the resplendent Milky Way above the most beautiful locations in the world. Nightscape astrophotography is among the easiest and most enjoyable pursuits for amateurs today, and is by far the most accessible to everyone.

S&T contributing photographer Babak A. Tafreshi is the founder of TWAN (www.twanight.org) and is the 2009 co-recipient of the Lennart Nilsson Award for scientific photography. See more of his nightscapes at www.dreamview.net.

The post Tips for Shooting Great Nightscapes appeared first on Sky & Telescope.

Categories: Astronomy

This Week’s Sky at a Glance, August 7 – 15

Sky and Telescope - Fri, 07/08/2015 - 17:05

 

Use binoculars during dawn to look for Mars below Castor and Pollux.

Now the waning Moon helps point the way to Mars.

Do some ancient Egyptian astronomy! If you're out to catch Mars low in the dawn, wait a bit longer to see if brighter Sirius becomes visible yet far off to its right. Prepare for the flooding of the Nile.

Friday, August 7

• Very low in the west after sunset this evening, Jupiter, fainter Mercury, and much fainter Regulus form a tight, fingertip-size triangle less than 1° wide. Bring binoculars or a wide-field telescope to look for them just above the horizon, a little to the right of due west, about 20 minutes after sunset.

• Today is the midpoint of astronomical summer, halfway from the June solstice to the September equinox. The exact moment: 8:29 a.m. Eastern Daylight Time (12:29 UT).

• The Moon, just past last quarter, rises around 1 a.m. tonight local time. By early dawn Saturday morning the Moon shines high in the east, forming a triangle with Aldebaran to its lower left and the Pleiades to its upper left.

• In early dawn these mornings, use binoculars to look for Mars below Castor and Pollux, as shown at right.

Saturday, August 8

• Seeing any early Perseid meteors yet? The Perseid shower should peak late this Wednesday night, August 12–13. The sky will be moonless. See Plan for the Perseids!

Sunday, August 9

• The two brightest stars of summer are Vega, overhead soon after dark, and Arcturus in the west. Vega is a white-hot, type-A star 25 light-years away. Arcturus is a yellow-orange-hot K giant 37 light-years distant. Their color difference is plain to the eye.

Monday, August 10

• Altair shines high in the southeast after dark. Just above it is little orange Tarazed. A bit more than a fist-width to Altair's left, look for Delphinus, the Dolphin, leaping leftward.

Tuesday, August 11

• The red long-period variable star Chi Cygni is near maximum! As of August 7th it was reported at magnitude 4.5. See the article and comparison-star chart in the August Sky & Telescope, page 51.

Wednesday, August 12

• The Perseid meteor shower should be at its peak late tonight, ideally so for North America. And there's no moonlight. Bundle up warmly (it gets cold under a clear, open August sky late at night), and lie back in a reclining lawn chair. You may see about a meteor a minute on average. The later you watch the better.

See Plan for the Perseids! More is in the August Sky & Telescope, page 48.

Thursday, August 13

• These moonless August nights are prime Milky Way time. After dark, the Milky Way is a great, mottled glowing band running from Sagittarius in the south up and left across Aquila and through the big Summer Triangle very high in the east, then on down through Cassiopeia to Perseus low in the north-northeast.

Friday, August 14

• This is the time of year when the Teapot asterism of Sagittarius stands highest in the south soon after dark. The Teapot is about the size of your fist at arm's length. It's tipping and pouring to the right, from its triangular spout.

Saturday, August 15

• Spot Saturn in the southwest after dark. The brightest star left or lower left of it is orange Antares. Draw a line from Antares through Saturn, extend the line almost as much farther on, and you hit fainter Beta Librae (Zubeneschamali). Much farther on, you come to Arcturus.

__________________________

Want to become a better astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy.

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but it's still less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The standards are the little Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and once you know your way around, the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the beloved if dated Burnham's Celestial Handbook.

Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (meaning heavy and expensive). As Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."

This Week's Planet Roundup

Venus a week before inferior conjunction. Damian Peach shot this image in broad daylight on August 8, 2015, at 13:59 UT, using a 900-nm infrared filter on his 14-inch scope. Note the faint cusp extensions slightly beyond the 180° ring that Venus would show if it had no atmosphere to scatter sunlight. Imaging in infrared "greatly helped with contrast," writes Peach. "The scope aperture was also masked down to prevent stray light entering." (Venus was 13° from the Sun.) "I also installed an active cooling system on the scope today, which seem to help as there were periods of quite good seeing at times."

Mercury, brighter Jupiter, and much fainter Regulus form a tight, fingertip-size triangle very low in the west in bright twilight on Friday the 7th. They're magnitudes –0.5, –1.7, and +1.4, respectively. Bring binoculars or a wide-field telescope to look for them just above the western horizon 20 minutes after sunset. For the rest of the week Mercury remains in view, but Jupiter and Regulus slide down out of sight.

Venus is out of naked-eye sight as it nears its August 15th conjunction between us and the Sun (inferior conjunction).

Mars (dim at magnitude +1.7) is becoming visible low in the glow of dawn. Look for it a little above the east-northeast horizon 45 to 30 minutes before sunrise. Bring binoculars. Don't confuse it with Pollux or Castor above it, or Procyon rising into view off to its right.

Saturn (magnitude +0.5, in Libra) shines in the south-southwest at nightfall, to the right of upper Scorpius. Fiery orange Antares, less bright, twinkles 13° to Saturn's left or lower left. Delta Scorpii is the brightest star more or less between them.

Uranus (magnitude +5.8, in Pisces) and Neptune (magnitude +7.8, in Aquarius) are in the southern sky well before the beginning of dawn now. Finder charts for Uranus and Neptune.

__________________________

All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.

Eastern Daylight Time (EDT) is Universal Time (UT, UTC, or GMT) minus 4 hours.

__________________________

“This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours.”

— Neil deGrasse Tyson, 2014

 

The post This Week’s Sky at a Glance, August 7 – 15 appeared first on Sky & Telescope.

Categories: Astronomy

Aloha to the World’s Astronomers

Sky and Telescope - Fri, 07/08/2015 - 04:02

Hawai‘i is currently hosting the biggest astronomy conference worldwide, the general assembly of the International Astronomical Union, to address current issues in astronomy.

The ocean breeze, dancing palms, sandy beaches — it’s a recipe for paradise. Add about 3,000 astronomers from more than 75 nations, and you’ll have a picture of the 29th IAU’s General Assembly. The 11-day event will present 3,500 selected talks and posters in several symposia and focus meetings. It will also include evening discourses, public talks, and outreach events such as stargazing sessions and planetarium programs.

A Welcome

At the Opening Ceremonies of the IAU, officials bestowed the $500,000 Gruber Cosmology Prize on researchers Jeremiah Ostriker, John Carlstrom, and Lyman Page.
Babak A. Tafreshi

The meeting is hosted in Honolulu, co-organized by the American Astronomical Society and greatly assisted by the University of Hawai‘i. At the opening ceremony on August 3rd, the mayor of Honolulu and the state governor of Hawai‘i welcomed the participants and bridged the Hawaiian ancient culture and modern society with the night sky.

Prominent speakers from the astronomical community included Meg Urry, the President of the American Astronomical Society, and France Cordova, the director of the National Science Foundation in Washington, D.C. and former NASA Chief Scientist. She was the highest ranked authority of the US government at the event. The program also included the 2015 Gruber Foundation Cosmology Prize (US$ 500,000), awarded to Jeremiah Ostriker, John Carlstrom, and Lyman Page for their contributions to the study of the universe on the largest scales.

Hawaiian dancers perform at the IAU opening ceremony.

The opening ceremony enlightened me on the intriguing word “aloha." The greeting can simply mean hello, but it can also convey gratitude, a hope for peace, and compassion for others. All the speakers began their speeches with “Aloha,” but the context for each was different. Guest speakers used it as a respectful salutation that showed their understanding of cultural values.

Local representatives used the word with even deeper meanings, as they continue to seek a difficult balance: supporting the advancement of science (including both its educational and economic aspects), while also respecting the voice of local islanders who wish to stop further construction on Mauna Kea.

The Mauna Kea Challenge

This artist's conception shows an aerial view of the Thirty Meter Telescope on top of Mauna Kea.
TMT

The 4,200-meter (13,800 feet) dormant volcano is not only Hawai‘i’s highest point, it’s also one of the world’s most stunning mountains. The peak is more than 10,000 meters tall, though most of it is submerged in water. The summit’s atmosphere and climate, as well as its dark skies, are extremely well suited to advanced astronomical observations. Some of the world’s most prominent and scientifically important telescopes, such as Keck Observatory, have been built there.

But Mauna Kea is not only valuable to astronomers. It is also the most sacred mountain in Hawaiian mythology, one that tradition had allowed only the highest-ranked members of the community to visit. Construction of the Thirty Meter Telescope (TMT) on the summit, scheduled to receive first light in 2022, has raised a local movement against the project. The conflict dates back to the earliest stage of the observatory’s construction in 1960s but for decades scientists and native islanders had worked together for the benefit of science and the local community.

The giant observatory would be one of the future game-changers to explore the universe, along with the 39-meter European Extremely Large Telescope and the 25-meter Giant Magellan Telescope in Chile.

Protestors convened in front of the IAU meeting in Honolulu to protest the Thirty Meter Telescope's construction.
Babak A. Tafreshi

On Tuesday, I attended the protesters’ press conference in front of the IAU conference venue. The opposition’s voices spoke with emotion about an issue that for them is largely spiritual. Mauna Kea is sacred to Hawaiian culture and has become a symbol for their spiritual and political survival. Moreover, though TMT officials insist the construction involves minimal environmental impact, the speaker of the Hawaiian community emphasized that we should protect the Earth and the environment before exploring the sky.

Astronomers spend years to develop projects such as the TMT, building new instruments and working on scientific proposals, as well as dealing with shrinking budgets and geographical and political boundaries. But they must also meet the environmental and cultural aspects of their selected site. This is particularly true in the digital age: opposition to TMT’s construction has been heard widely through the use of social media.

The speakers at the press conference also appeared to consider astronomy as a pure curiosity, but that’s where science communicators can help: we can show the public how space sciences and astronomy positively affect our daily life, revolutionize our understanding of our Earth, and provide new systems to monitor our fragile natural environment.

In the next two posts about the IAU conference I will talk about some of the interesting science to be presented here and new plans of the union. Also, keep up with the IAU’s goings-on in the event’s daily electronic newspaper, featuring that day’s talks and breaking IAU news.

Diamondhead Crater rears above Honolulu, this year's base of the IAU's tri-annual general assembly.
Babak A. Tafreshi

The post Aloha to the World’s Astronomers appeared first on Sky & Telescope.

Categories: Astronomy

Brown Dwarfs Form Like Stars

Sky and Telescope - Thu, 06/08/2015 - 18:00

Recent radio observations support the idea that brown dwarfs form like full-fledged stars do.

Brown dwarfs, which bridge the gap between stars and planets, have been an exciting target for astronomers since their discovery in the mid-1990s. Since that time, we’ve observed and classified hundreds of these objects, but the details of how they form still remain an active area of research. The answer to a simple question, "Do brown dwarfs form in a method similar to stars, or do they form more like planets?" has eluded astronomers for decades.

Artist's conception of a very young, still-forming brown dwarf, with a disk of material orbiting it and jets of material ejected outward from the poles of the disk.
Credit: Bill Saxton / NRAO / AUI / NSF

The general picture of star formation is relatively clear. Massive clouds of gas, millions of times more massive than the Sun, collapse due to gravity. As the collapse ensues, clumps within the cloud begin to pull in material more rapidly than other, less dense regions. These overdensities create immense pressures and temperatures inside themselves (reaching over 25 million degrees Fahrenheit!). Eventually, the conditions for nuclear fusion are reached, and a star is born.

During this time, the star is still accreting material at a much smaller rate, spinning rapidly, and producing large magnetic fields. Thanks to the conservation of angular momentum, the rapid rotation also forms a disk out of the protostar’s birth cloud, in which smaller gravitational collapses may happen, resulting in planets.

But it’s unclear if brown dwarfs arise the same way. A group of astronomers led by Oscar Morata (Academia Sinica, Taiwan) has published results in the July 1st Astrophysical Journal that might go a long way in answering that question.

Brown dwarfs are often referred to as "failed stars." Spanning a mass range of about 13 to 80 times that of Jupiter, brown dwarfs lack sufficient pressures and temperatures in their cores to ignite nuclear fusion, the process that generates starlight. They start off with surface temperatures about one-third that of our Sun, and most of that heat is generated as the cloud that forms the brown dwarf collapses under its own gravity. This makes the youngest brown dwarfs the hottest and brightest members of their class. As time passes they slowly cool, like fireplace embers — but over billions of years.

The team targeted young brown dwarfs, because they haven't had a chance to cool off and are thus intrinsically brighter than older ones. The team was searching for jets, which astronomers commonly see coming from protostars but have not observed often from forming brown dwarfs.

Morata and his team imaged 11 proto-brown dwarfs using the Karl G. Jansky Very Large Array (VLA) radio telescopes in New Mexico. These objects are still in the process of forming and are still gravitationally accreting gas and dust. All of the young brown dwarfs sit in a star-forming region in Taurus about 450 light-years away, with an age of only about 1 million years.

Four of the young brown dwarfs showed radio emission due to jets, a hallmark of young, more massive stars. Jets are usually seen in young stars that are just forming, when the stellar magnetic fields are still very strong and the star is spinning rapidly. These magnetic fields can trap charged particles, supplied by strong protostellar winds, which emit radio waves as they accelerate around the fields. Observers have found that with normal stars, the strength of the magnetic fields, the amount of radio waves produced by particles spiraling through the jets, and the overall amount of proto-starlight produced are all related, with more massive (and therefore brighter) stars producing stronger magnetic fields and jets.

By comparing the strength of the radio waves emitted by the proto-brown dwarfs to the overall amount of light these forming objects produce, the team was able to show that these young brown dwarfs display the same behavior as their more massive stellar cousins.

“This is the first time that such jets have been found coming from brown dwarfs at such an early stage of their formation, and shows that they form in a way similar to that of stars," said Morata in an NRAO press release. "These are the lowest-mass objects that seem to form the same way as stars," he added.

This exciting discovery shows that brown dwarfs are more similar to stars than to planets. It also builds on past results, including computer simulations of star formation that not only also produced brown dwarfs, but a ratio of brown dwarfs to stars similar to that observed in our galaxy. Those simulations assumed that brown dwarfs formed in a similar way to stars, and the detection of jets further confirms this scenario. With new arrays such as ALMA coming online, we can expect to see more results on jets around brown dwarfs in the future.

 

Reference: O. Morata et al. "First Detection of Thermal Radiojets in a Sample of Proto-Brown Dwarf Candidates." Astrophysical Journal. July 1, 2015.

The post Brown Dwarfs Form Like Stars appeared first on Sky & Telescope.

Categories: Astronomy

Gigantic Protogalaxy in the Cosmic Web

Sky and Telescope - Thu, 06/08/2015 - 01:05

Astronomers have found that a massive filament of gas in the early universe actually seems to be a humongous, galaxy-forming disk.

Galaxy formation is a complicated affair. It can involve big smashups and nonchalant snacking, but as I explain in my feature article in S&T’s September issue, that’s only a slice of the story. One way that galaxies grow — and possibly the predominant way in the early universe — is from cold gas funneled like a pipeline into wells of dark matter.

This snapshot from a computer simulation shows a protogalaxy (central disk) growing by accreting cold gas from cosmic filaments (blue streams) in the early universe. Over time, hot gas (red) chokes off the filamentary inflow. The protogalaxy shown here is only one-fifth as wide as the disk recently discovered in the early universe, but the overall properties (given the scaling up) are similar.
Oscar Agertz

These dark matter wells are dense filaments in the weblike cosmic structure, along which galaxies form. Computer simulations suggest that cold-gas accretion was a big deal in the universe’s first couple billion years. After that, the halo of gas around a forming galaxy generally grew so hot that it choked off the pipeline (although not necessarily entirely). But observing cold-gas accretion in action is tough, because the gas is fairly diffuse and faint.

Last year, astronomers detected a large, bright filament of gas called UM 287 shining at us from about 11 billion years ago. It’s bathed in the glow — well, vicious radiation — of a nearby quasar, whose supermassive black hole spawns an ultraviolet beam that illuminates the filament and makes it fluoresce. At the time, the team estimated that the cosmic filament was about 10 times more massive than expected, given simulation results.

But it turns out the filament isn’t too massive, and for an interesting reason.

Christopher Martin (Caltech) and colleagues took a second look with the Palomar Cosmic Web Imager, a high-tech spectrograph they built and installed on the 5-meter (200-inch) Hale Telescope on Palomar Mountain in California. The spectrograph homed in on a particular wavelength called Lyman-alpha, which comes from cold neutral hydrogen that’s been irradiated by ultraviolet light. Shifts in the Lyman-alpha line toward redder or bluer wavelengths indicate the gas is moving along our line of sight. By analyzing the filament’s spectra, the team discovered that one part of the filament is moving toward us, while another section is moving away from us. In other words, the filament isn’t merely a filament: it’s a fuel line feeding a gigantic disk.

Big Disk in the Early Universe

The disk is huge: it’s about 400,000 light-years across, or three to four times the size of the Milky Way’s spiral disk. The rotational velocity suggests it’s sitting in a halo of 10 trillion solar masses’ worth of dark matter, 10 times larger than the halo our galaxy inhabits, the team reports August 5th in Nature. There’s even a hint of star formation in its center, but the team isn’t sure of that yet.

“Overall, it’s hard to say with certainty that they’re definitely seeing a cold-flow disk — as opposed to some other phenomenon that just happens to look like a cold-flow disk,” says Kyle Stewart (California Baptist University), whose team has simulated the growth of these objects. “But when you look at all the observable properties of cold-flow disks from the simulations to determine what they should look like in the real universe, in my opinion, it’s amazingly similar to what these authors have just observed.”

One notable parallel is the disk’s high rotation speed: about 500 km/s (1 million mph), twice that of the Milky Way’s disk. That supports the idea that the disk is forming from cold gas channeled in via the filament it's grafted onto, and not from hot gas falling in from all sides.

You can think of the difference like two ways of filling a tub with water. The dark matter well is like a colossal, circular tub. The tub is spinning slowly, because the dark matter’s angular momentum was conserved as gravity collapsed it into a big clump. If infalling gas were hot and flowing in from all sides, the gas would spin slowly with the dark matter, like water gently flowing into a big rotating bowl. But if you shoot the water into the tub from a hose, it’ll whisk around the tub’s sides much faster than the tub itself is spinning. Theorists think the cold flow shoots in with a lot more spin to it because the cold stream is concentrated, and thus more susceptible to the dark matter’s tidal forces, Martin explains.

Since it’s so massive so early in the universe, the disk likely grew into an elliptical, Martin suggests. Depending on what coalesced around it, maybe today it’s even sitting at the center of a big galaxy cluster.

 

Reference: D. C. Martin et al. “A giant protogalactic disk linked to the cosmic web.” Nature. Online August 5, 2015.

Want to know more about how galaxies grow? Pick up a copy of Sky & Telescope's September 2015 issue and read our in-depth feature.

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Categories: Astronomy

Let’s Get Serious About Ceres

Sky and Telescope - Thu, 06/08/2015 - 00:26

With Ceres coming alive in the latest Dawn images, why not step outside and see it with your own eyes? We also look at the history of its discovery and suggest a way to honor its discoverer, Giuseppe Piazzi.

598-mile-wide Ceres spends its time in the inner asteroid belt between Mars and Jupiter. It's covered in craters, lined with fissures and also hosts a cluster of enigmatic white spots that might be ice inside 57-mile-diameter Occator crater (top).
NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

With the Dawn spacecraft now spiraling down to its third and closest-yet science orbit around Ceres, what better time to see this small, unique world with your own eyes? As amateur astronomers, it's a thrill to behold an object of such intense scrutiny from our own backyards. That's even more the case when spectacular images are available to feed our imaginations, turning a pinprick of light into a rumpled sphere overrun with icy craters and vaporous white spots.

Ceres is only 16 minutes away as light flies, or 182.3 million miles from Earth, and shines at magnitude 7.6. It was a tad closer and brighter in late July, but it also rose at a less convenient hour.

In mid-August, the dwarf planet comes into view not long after nightfall. With one caveat. From mid-northern latitudes, it's rather low in the southern sky. Still, if I can see it from northern Minnesota in binoculars, chances are, you can, too.

The Moon steps away from the evening sky this week, making for ideal viewing conditions. To observe Ceres, find a location with an open view to the south. My southern sky's far from ideal, but a gap in the tree line lets me sample celestial objects as far south as –35° declination for up to a half hour. Ceres will arc slowly westward in eastern Sagittarius near the Capricornus border the next two months fading a bit to magnitude 8.0 by late August.

Looking south-southeast on August 7th from Denver around 10:30 p.m. local time, you'll find Ceres 15° high in Sagittarius. The asterism of four 4.5- to 4.8-magnitude stars I've dubbed the "Cross" will point you in its direction. Start with this map and then use the more detailed version below.
Source: Stellarium

The maps will help you get there. Ceres looks exactly like a star in 8×40 or similar binoculars. As you watch evening to evening, you'll see the dwarf planet amble west in retrograde motion, much like the other outer planets do around the time of their opposition.

Looks like we've got luck on our side the next few days as Ceres pairs up with a slightly fainter 7.7-magnitude star. The chance encounter provides an opportunity to easily spot Ceres' westward journey — watch them separate in the coming nights.

Detailed map showing Ceres' path in eastern Sagittarius from August 5 to September 9, 2015, around 10 p.m. CDT. Stars are shown to magnitude 8 with a few relevant ones labeled with magnitudes. Click to download a large version. First locate the Handle of the Teapot (far right), then sweep to the east in your binoculars to "The Cross". It points to a 6.2-magnitude star. This is your "jumping off" point to locate the asteroid. 
Source: Chris Marriott's SkyMap

The Discovery of Ceres

Giuseppe Piazzi discovered Ceres quite by accident on the first evening of the 19th century (January 1, 1801) while making stellar position measurement from his observatory in Palermo, Italy. Unbeknown to him at the time, a group of 24 astronomers headed up by Baron Franz Xaver von Zach, a German-Hungarian astronomer, were preparing to make a systematic search for a hypothetical "missing planet" predicted by the Titius-Bode law between Mars and Jupiter. Fittingly, they named their group the Himmels Polizei (Celestial Police).

Italian Catholic priest and astronomer Giuseppe Piazzi around 1807 with his new "star", the dwarf planet Ceres.
Public Domain

Despite Piazzi's respected reputation, he had not been invited to become a member. No matter. That night around 8 p.m. he spotted a tiny new "star" in the "shoulder of Taurus" (below the Pleiades near the border with Aries) and announced it to the press the same day as a comet.

Piazzi kept track of the object through the the 23rd, observing it on a total of 13 nights. The more he looked, the more convinced he became it might be something more than a comet. Here's an excerpt from a letter Piazzi sent to astronomer Barnaba Oriani in 1801, sharing his observations:

"I have announced this star as a comet, but since it shows no nebulosity, and moreover, since it had a slow and rather uniform motion, I surmise that it could be something better than a comet."

Piazzi's observation echoes that of William Herschel just 20 years earlier when Herschel chanced across what he thought at first was a new comet, but turned out to be Uranus, the first new planet discovered since antiquity.

By the time Piazzi's data reached other astronomers in the spring of 1801, Ceres was near conjunction and too close to the Sun to observe. Astronomers worked to create a set of ephemerides they could use to track it down when it reappeared in the morning sky that summer. Unfortunately, Piazzi had observed it along too short of an arc (just 3°) and computing an accurate orbit wasn't possible.

By August, astronomers were getting desperate with some starting to wonder if the new planet even existed. Enter 24-year-old mathematician Carl Friedrich Gauss. He took it the orbit problem to heart and wrestled an accurate solution in a little more than a month. Using Gauss's new ephemerides, von Zach finally spotted Ceres on December 7, 1802 . . . and the rest is history. For more fascinating reading on the discovery of Ceres, click here.

Craters are the dominant landform on Ceres, and as of July 2015 about a dozen had received official names. Color coding indicates altitude, from a low (dark blue) about 7½ km (5 miles) above the surface mean to highs (red) about 7½ km above it.
NASA / JPL / UCLA / MPS / DLR / IDA

Given Piazzi's wonderful discovery, you might expect to see his name on a large crater or other prominent feature on the dwarf planet. Yet if you peruse a recent map with formally approved names, he's nowhere to be found!

Maybe the IAU Working Group for Planetary System Nomenclature, responsible for the naming of features on solar-system bodies, has a special spot in mind, but I wonder. The group has approved two themes for use on Ceres — gods and goddesses of agriculture and vegetation from world mythology for craters and names of agricultural festivals for other features.

1 Ceres' track across Sagittarius and Capricornus from August 5 to December 3, 2015. Click to download a large version.
Source: Chris Marriott's SkyMap

Hmmm. That doesn't seem to leave room for Giuseppe unless the group allows exceptions similar to to Venus's Maxwell Montes (after Scottish physicist James Clerk Maxwell), the only male presence among a myriad of mythological goddesses. It, along with Alpha and Beta Regio, were first seen in Arecibo radar images in the 1960s before the naming convention was adopted.

Sure, you'll find a Piazzi crater on the Moon and even asteroid 1000 Piazzia, but there's also a Tombaugh crater on Mars and the asteroid 1604 Tombaugh, named for Pluto's discoverer. His name now graces (pending approval) the icy plains of Pluto's Tombaugh Regio.

It only seems right to honor Ceres' discover with a prominent feature on the dwarf planet itself. How about those bright, white spots or the 3-mile-high pyramid mountain? I think you'd agree that Piazzi's magnificent orb not only deserves but a look with your own eyes but his name, too.

Read all about Dawn's arrival at Ceres and what it will do there in the April 2015 issue of Sky & Telescope.

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Categories: Astronomy

Shedding New Light on Near-Earth Asteroids

Sky and Telescope - Tue, 04/08/2015 - 22:15

Students captured some amazing videos of near-Earth asteroids this past month, demonstrating a powerful tool for learning about some of our nearest celestial neighbors.

Astronomers have been bouncing radar beams off asteroids since the close passage of 1566 Icarus in 1968. Now, students participating in a specialty summer school carried out a detailed series of observations of asteroid 2015 HM10 using the Green Bank Telescope (GBT), a single 100-meter radio dish, and NASA’s Deep Space Network radar transmitter at Goldstone, California.

The student team had a close target: the asteroid passed just 440,000 kilometers (1.1 times the Earth-Moon distance) from our planet on July 7th. But the near pass posed a challenge too, since the asteroid moved quickly across the sky.

Capturing an Asteroid with Radar

Student Participants in the NRAO Single Dish Summer School Program.
K. O’Neil / NRAO / AUI / NSF

The students were participating in a specialty program that gives astronomy graduate students and postdocs an opportunity to gain practical experience in single-dish radio astronomy, and in particular a special technique called bistatic radar.

This technique helps paint a picture of a targeted asteroid in unprecedented detail. Usually, radio astronomers use a single radio dish to transmit and receive radar. But the reflected radar signal is typically much weaker than the transmitted signal.

“In bistatic observations, we use one telescope to transmit and another to receive,” says Marina Brozovic (NASA / JPL). “It is to our advantage to receive with a larger telescope, because a larger surface area means stronger signal.” In the case of the asteroid observations, the gigantic GBT served as the receiver for the radar transmitted from Goldstone. “We can double the signal strength if we receive at GBT,” Brozovic adds. “As such, GBT has been a great asset in enhancing radar observations.”

The bistatic technique is especially useful for exceptionally close asteroid passages (those that pass within twice the distance to the Moon), because it becomes difficult to switch a single antenna between the send and receive mode due to a short light travel time.

At 80-meters across on its longest axis, the asteroid 2015 HM10 is slightly larger than a Boeing 777-300ER airliner from nose-tip to tail. It orbits the Sun once every 4.06 years, and the July 7th passage was the asteroid’s closest pass to Earth this century. The team’s project captured 42 radar images with a resolution of about 3.75 meters per pixel, showing the asteroid spinning every 22 minutes.

Video animation of 2015 HM10 during closest approach.
NASA / JPL-Caltech / NRAO / AUI / NSF

Meanwhile, NASA scientists applied the same bistatic radar technique in order to image another asteroid, 2011 UW158, on July 19th as it passed 2.4 million kilometers from Earth. Images with a resolution of 7.5 meters per pixel revealed parallel ridges on the elongated asteroid.

Watching a Tumbling Space Peanut

Just last week, astronomers released new images of asteroid 1999 JD6 using the same technique. The rock passed 4.5 million miles from Earth on July 24th (19 times the distance between the Earth and Moon), and the images clearly show a two-lobed contact binary asteroid spinning around every 7.5 hours. About 15% of the near-Earth asteroids that scientists have resolved display a dumbbell shape , and the Rosetta mission discovered the same double-lobed structure on Comet 67P/Churyumov-Gerasimenko.

A sequence of images of ‘peanut asteroid’ 1999 JD6 on closest approach.
NASA / JPL-Caltech / GSSR

In addition to asteroids’ shape, radar observations reveal their spin, surface features, and sometimes they even reveal surprises, such as the tiny moon found orbiting the asteroid 1998 QE2 during its passage 5.8 million km from Earth on May 29, 2013. The more recent radar images of asteroid 2004 BL86 on January 27, 2015, also revealed a previously detected moon-like companion.

This video, captured earlier this year, shows asteroid 2004 BL86 and its previously detected moon.
NASA / JPL-Caltech / NRAO / AUI / NSF

And there’s much more in store for characterizing asteroids in this way. “We have a busy observing year ahead of us, and [NASA] will again be joining forces with our colleagues at Green Bank Telescope on at least several asteroids,” Brozovic says.

The next one on the list? NEA (413577) 2005 UL5, a 300-meter asteroid that will approach Earth within 6 lunar distances in late November — this asteroid, Brozovic adds, will be one of the best targets this year.

Expect to see more amazing asteroid images in the near future.

What role did asteroids play in previous extinctions on Earth? Could we divert a threatening asteroid? Could we ever mine asteroids? These are among Astronomy's 60 Greatest Mysteries.

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Categories: Astronomy

Blue Moon over Staffordshire

Sky and Telescope - Tue, 04/08/2015 - 21:28

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Categories: Astronomy

Draco Trio of Galaxies

Sky and Telescope - Tue, 04/08/2015 - 21:28

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Categories: Astronomy

Blue Moon

Sky and Telescope - Tue, 04/08/2015 - 21:28

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Categories: Astronomy

Eve of the Blue Moon

Sky and Telescope - Tue, 04/08/2015 - 21:28

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Categories: Astronomy

The Temple of Stars

Sky and Telescope - Tue, 04/08/2015 - 21:27

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Categories: Astronomy

Deep Sky with your DSLR

Sky and Telescope - Mon, 03/08/2015 - 21:00

Getting started in astrophotography has never been easier.
By Michael A. Covington in the Sky & Telescope June 2012 issue.

Astrophotography with digital single-lens reflex (DSLR) cameras spans all facets of amateur astrophotography. Today’s camera models have much lower noise than in the past and more features useful to amateurs. In the accompanying text, Michael A. Covington explains how you can capture spectacular images like the one above of the Pipe Nebula in Sagittarius.
Michael A. Covington

There's no question that digital single-lens reflex cameras (DSLRs) are the most versatile cameras available today. No other device can go from shooting your children’s birthday party in the backyard to recording distant galaxies through a telescope without needing any modifications. DSLRs have truly thrust open the door of astro-imaging to anyone with an interest in shooting the night sky.

Several factors make DSLRs good for astronomy. Most of the cameras are designed to use the same lenses as their 35-mm film precursors, and they have relatively large sensors compared to their point-and-shoot counterparts. The common APS-C size CMOS sensors in many consumer DSLRs are about 65% as big as 35-mm film, and about as large as many mid-range astronomical CCD cameras.

Unlike film, the CMOS sensor in a DSLR has no reciprocity failure; it never forgets a photon. (Well, hardly ever.) A 2-minute exposure is long enough to capture a respectable image of the Orion Nebula. In 10 minutes with a modest telephoto lens, you can record 16th-magnitude stars. And DSLRs don’t require you to bring along a computer when you’re shooting the night sky.

There are many DSLR cameras available for purchase, but Canon manufactures the most popular ones for astrophotography. It is the only DSLR maker that has actively cultivated the astronomy market, at one time even marketing a DSLR specifically for astrophotographers (the 20Da). This model has long since been discontinued, but Canon has incorporated many of its best features useful for astrophotography into current models.

Other DSLRs from Nikon and Pentax are similar, differing mainly in the way functions are accessed and image files are formatted. Virtually all current DSLRs block the astronomically important far-red end of the visible spectrum where hydrogen gas fluoresces. To increase their camera’s red sensitivity, many astrophotographers have had their cameras modified. They remove the camera’s infrared-blocking filter and replace it with a filter that transmits more of the red light from hydrogen emission. Those daring individuals willing to tinker with their cameras can purchase a modified infrared-blocking filter and do the work themselves, or you can send your camera to Hap Griffin (www.hapg.org) or Hutech (www.hutech.com) to have the filter replaced for you. Once the camera is modified, you’ll have to set a custom color balance to shoot pleasing daytime images.

Most DSLR cameras have filters that block the far-red end of the spectrum to produce natural-color daylight images. Left: Unfortunately, these stock filters block much of the reddish nebulosity in the Milky Way, as seen in this image of Orion’s Belt. Right: When the stock filter is replaced with a custom filter, the resulting image of Orion’s Belt reveals much more nebulosity.
Alan Dyer (2)

If you’re shopping for a new DSLR with astrophotography in mind, one particular feature worth seeking out is known as “Live View.” This feature allows you to turn on the sensor and view a live video on the camera’s rear LCD screen. This makes focusing your lens or telescope a breeze compared to other methods. If you don’t have Live View, you’ll need some form of focusing aid, or you can confirm focus by taking short 5-second exposures and immediately viewing them on the rear screen.

Shooting Stars

Once you’ve picked your camera, there are a few additional accessories you’ll need to start shooting the night sky. The first is a device that will let you shoot long exposures without touching the camera. You can make single exposures up to 30 seconds by pressing the shutter release on the camera, and setting a delay so the vibration from pressing the button will have died away before the shutter opens. For longer exposures, you can use a special cable release with a built-in intervalometer. It allows you to program a series of long exposures and eliminates the need for a delay between images. Versatile, inexpensive cable release intervalometers are made by Phottix (www.phottix.com) and other accessory makers, and are easy to find on Amazon.com or ebay.com. Make sure you select the proper model for your particular camera.

You’ll also want a tripod for your first foray into DSLR astrophotography. Even if your primary goal is to shoot close ups of deep-sky objects through your telescope, shooting simple camera-on-tripod shots will help familiarize you with the functions of your camera that you’ll use for all types of deep-sky astrophotography. The tripod also comes in handy for shooting conjunctions, wide-field photos of the Milky Way, and meteor showers — popular targets for all astrophotographers.

Because DSLRs look and feel a lot like 35-mm film cameras, the way you attach one to your telescope is similar. To start shooting the sky with a DSLR, you’ll need a few accessories, such as an intervalometer (far left) that can automatically shoot multiple long exposures, and a T-ring adapter (bottom right center) for your particular model.
S&T / Sean Walker

Under a starry, moonless sky, put your camera on your tripod. Use a wide-angle lens at its widest f/stop (lowest f/number) and focus manually on a bright star using live focus, if the feature is available with your camera. Zoom in on the live-focus view to help achieve the sharpest focus. Set the ISO speed to 1600 and expose for 30 seconds. You’ll get a picture that shows plenty of stars and possibly some of the brighter deep-sky objects.

A few nights of practice will familiarize you with your camera’s features that are beneficial for astrophotography, such as mirror lock-up, noise reduction, and programming sequences of exposures on your intervalometer.

If you long for deeper exposures with round stars, you can “piggyback” your camera on top of your telescope, photographing the sky through your camera lens while using the telescope to track. With this method, you’ll find that the standard 18-55-mm zoom lens that comes bundled with many DSLRs isn’t very good for astronomy; it’s slow (usually no faster than f/4.5) and less sharp than many fixed-focal-length lenses. Also, being a zoom, it may shift focal length or focus as the telescope tilts to track the sky.

Fixed-focal-length lenses are better suited for astrophotography. You can of course buy superb telephoto lenses from Canon, Sigma, and other makers. Here’s a useful tip: adapters are available to convert old manual-focus Olympus, Nikon, Pentax, Contax/Yashica, and screwmount lenses to work on your Canon EOS or Nikon DSLRs. Because autofocus doesn’t work for deep-sky astrophotography, you can use old manual-focus lenses that are much less expensive than the newest lenses on the market. These adapters are available from Fotodiox (www.fotodiox.com).

If you want to try your hand at shooting objects through your telescope, you’ll need an adapter. This usually consists of a T-ring and an adapter that couples your camera to your telescope in place of an eyepiece. With this setup, you can immediately take photographs of the Moon using your telescope as a camera lens. To take pictures of deep-sky objects, you can experiment and make exposures of 5 seconds or more to test how long your telescope mount will track before stars appear as streaks. Even most high-end telescope mounts require an autoguider or other special measures to compensate for errors in the mount’s gears, wind buffeting, or other variations in tracking.

Image Processing

At high ISO settings, DSLRs are far more sensitive than the best films of the past. This 5-second exposure with a Canon 40D at ISO 1600 and a 50-mm f/2.8 lens captures 6th magnitude stars and the bright globular cluster Omega Centuri at lower right.
Michael A. Covington

No matter what kind of astrophotography you’re doing, the image that comes out of the camera isn’t usually the finished product. A short, fixed-tripod exposure often appears too dark, while a 2- or 3-minute guided exposure is likely to look too bright because of light pollution. That’s normal. Any automatic white balance in your camera is not usually applicable to deep-sky astrophotos because the subject is too faint for the camera’s computer to make an accurate judgment. You can adjust all of these settings with image-processing software. Although some programs that come with digital cameras offer rudimentary adjustment abilities, I highly recommend acquiring a software program specifically geared toward DSLR astrophotography. These programs are necessary to get the most out of your images.

Some popular programs available for DSLR astrophotography include MaxIm DL (www.cyanogen.com), ImagesPlus (www.mlunsold.com), Nebulosity (www.starklabs.com), and DeepSkyStacker (http://deepskystacker.free.fr). Most are available as a trial before purchase, and DeepSkyStacker is freeware.

Once you’ve chosen your processing software, two steps will immediately make your images better. The first is dark-frame calibration. When you take an exposure longer than a few seconds with most DSLRs, you’ll see a random scatter of colored pixels — red, green, and blue specks — indicating places where the sensor has what are known as “hot pixels.”

Every deep photograph recorded with a DSLR requires some adjustment. The author shot this picture of Comet Holmes from his urban backyard on November 15, 2007. Note the reddish background sky (left), which was easily corrected using image-processing software (right). This piggybacked 3-minute exposure was taken with a Canon 40D at ISO 400 using a 300-mm f/5 lens.
Michael A. Covington

The best way to get rid of hot pixels is to subtract a dark frame, a picture taken with no light reaching the sensor, but in all other respects just like the original, with the same exposure time, ISO setting, and sensor temperature. The dark frame will have the same hot pixels, so subtracting it from your picture will remove them. Most DSLRs can do this for you automatically if you turn on your camera’s long-exposure noise-reduction function. Then, after you take a long exposure, the camera will immediately take another one just like it with the shutter closed, perform the subtraction automatically, and record the resulting image. Although this feature is handy and guarantees that the dark frame matches all the settings of the original exposure, it takes up precious time that you could be using to record images.

The alternative is to take one or more dark frames manually with the lens cap on and subtract them later with software. Preferably, take several — at least a half dozen — so that software can average them to eliminate random noise. One set of dark frames can serve for pictures of several celestial objects taken on the same evening with the same exposure time and ISO setting.

Stacking multiple exposures helps to reveal faint nebulosity. Combining eight 4-minute exposures shows the Messier objects (from top to bottom) M21, M20, and M8 in Sagittarius.
Michael. A Covington

Besides dark-frame calibration, the second technique that will make your images smoother is to shoot multiple exposures of your target and combine them. This technique, known as stacking, has many advantages. You can get an hour’s exposure without needing an hour of perfect guiding. If you have guiding problems, you can take many exposures and simply toss out the poorly tracked ones. You can also avoid reaching the sky fog limit because no single exposure is excessively long. Stacking algorithms in image-processing programs can automatically discard airplane trails, random hot pixels, and other large discrepancies between the images you are combining. And when you stack multiple exposures, the noise level in the stacked image is reduced proportional to the square root of the number of exposures you combine.

There are limits, of course. You can’t stack 3.6 million 1/1000-second exposures and get the equivalent of an hour-long exposure. The individual exposures have to be long enough for a useful image. That is typically 5 to 10 minutes, unless tracking limitations compel you to go shorter.

Stacking and dark-frame subtraction are also best done with raw files, not JPEGs, because JPEGs have been stretched nonlinearly for display, and data is thrown away in the compression process that makes JPEG files small compared to raw format. After dark-frame calibration and stacking, you can then adjust the brightness, contrast, and color balance of your image and perhaps sharpen it if necessary before saving the final version.

As you improve at recording data, you can learn many additional tricks and techniques to squeeze even more out of your images. But the tips in this article will put you well on your way to taking great astrophotos while avoiding many pitfalls.

Michael Covington is an avid astrophotographer and author
of Digital SLR Astrophotography, which is available at
www.covingtoninnovations.com/dslr.

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Categories: Astronomy

Alan Stern: What We Found at Pluto

Sky and Telescope - Sat, 01/08/2015 - 05:04

It sounds like science fiction, but it's not: NASA's New Horizons mission explored the Pluto system this summer!

twitter.com

Exactly 50 years to the day after Mariner 4 became the first mission to explore Mars, New Horizons completed the first era of planetary reconnaissance by flying past Pluto on July 14, 2015. In my final "insider blog" for SkyandTelescope.com, I want to give you a recap of the main findings that came from the initial data returned from the spacecraft.

NASA’s New Horizons spacecraft took this image of Pluto with its Long Range Reconnaissance Imager (LORRI) on July 13, 2015. The color image has been combined with lower-resolution color information from the Ralph instrument acquired earlier. This view is dominated by the large, bright feature informally named Tombaugh Regio, roughly 1,000 miles (1,600 km) across. This is the last and most detailed image sent to Earth before the spacecraft’s closest approach on July 14th.
 NASA / JHU-APL / SwRI

Regarding Pluto, we found a wonderland of diverse geological expression, with both old and young surfaces, mountain ranges, polygon-subdivided ice plains, flowing glaciers, and possibly even evidence for subsurface liquids. Pluto's mountains require strong materials to survive (and not slump) over time, indicating Pluto's crust is likely to be composed of water ice, rather than a deep layer of frozen nitrogen, which is soft and malleable to form long-lived mountains.

We also found that Pluto was bigger — 2,374 km in diameter — than most past estimates. This larger true size, combined with Pluto's already well-known mass, means its true density is lower than we thought. So the ice fraction is higher (35% or 40%) and its rock fraction lower (60% or perhaps 65%).

Meanwhile, its tenuous atmosphere has a base pressure of less than 10 microbars (about half what ground-based measurements had predicted), and it contains widespread hazes, several new molecular species (including acetylene and ethylene).

Pluto's moon Charon, as seen by New Horizons on July 13, 2015, shows an array of landforms that has stunned mission scientists.
NASA / JHU-APL / SWRI

Regarding Charon, we found no evidence for an atmosphere — though the final verdict depends on data not yet back on Earth. We also found a more complex geological story than many had anticipated.

Most of us expected Charon to be little more than a battered ball of water ice and craters. Instead, we found tectonic ridges, chasms, and mountains, along with a strangely dark red stain covering its north polar region.

Next Steps

The New Horizons science team is now at work mapping both bodies and preparing to formally submit names for specific surface features to the International Astronomical Union. We've been naming features informally, drawing from the "OurPluto" name banks that New Horizons and NASA conducted with the public's help. Preliminary maps of both Pluto and Charon are below.

Although informal for now, these feature names follow an approved scheme and have been submitted to the IAU for approval.
NASA / JHU-APL / SWRI

Similarly, the initial, informal names used by the New Horizons team for the features on Charon, Pluto's largest moon, were selected based on input received from the OurPluto naming campaign.
NASA / JHU-APL / SWRI

Regarding Pluto's small satellites, we've learned the sizes of Nix (35 km in diameter) and Hydra (41 km), and our first looks reveal brightness and color variegation across their surfaces. We found their albedos (reflectivities) are higher than expected — so high in fact that both are likely ice covered. (Resolved images of Styx and Kerberos have not yet been returned as of this writing.)

New Horizons recorded these images of two of Pluto's four small moons. Nix has an irregular shape (seen here end-on in false color), about 42 km (26 miles) long and 36 km (22 miles wide. Hydra appears roughly spherical and is 55 km (34 miles) across.
NASA / JHU-APL / SWRI

Most surprising to me about Pluto's satellites, however, is that, despite searching with about 15 times more sensitivity than even the Hubble Space Telescope, we didn't find any more —not even one. Few on our science team would have predicted this, including myself.

The flyby of Pluto and its system of moons by New Horizons is complete, but over 95% of the data from that reconnaissance is still aboard the spacecraft, awaiting downlink to Earth. Getting all those observations back will take some 16 months and won't complete until the fall of 2016. So expect many more images and spectra and, from those, many more discoveries in the months ahead. New Horizons is a gift that will keep on giving.

Check out Alan Stern's first, second, and third previous blogs for SkyandTelescope.com.

The post Alan Stern: What We Found at Pluto appeared first on Sky & Telescope.

Categories: Astronomy

Microlensing Exoplanet Confirmed

Sky and Telescope - Sat, 01/08/2015 - 04:01

Astronomers have confirmed the existence of an exoplanet found via microlensing — the first time they’ve been able to successfully follow up on this method.

One of various methods astronomers use to hunt for planets around alien stars is microlensing. In a microlensing event, one star passes in front of another from our perspective, and this alignment — within a fraction of a milliarcsecond (1/3,600,000°) — boosts the light of the background star. It’s as though the closer star is a magnifying glass, amplifying the farther star.

In a microlensing event, a foreground star passes directly in front of a background star. The background star's light bends around the foreground star, which gravitationally lenses and magnifies the starlight. If a planet orbits the foreground star, it, too, will leave its own mark on the background star's light (the exact shape of the blip in the light curve often looks rather complex, depending on the nature of the system). Click here to see the full-size version on the Keck Observatory's website.
NASA / ESA / A. Feild (STScI)

If the closer, magnifying star has a planet around it, this planet can add an extra blip to the light curve of the boosted signal, which astronomers can detect. Astronomers can use the blip’s characteristics, such as its timing and magnitude, to calculate how far the planet is from its star and (indirectly) its mass.

Astronomers have found about three dozen exoplanet candidates via microlensing. But these candidates are difficult to confirm: observers need to either catch the closer star passing in front of another faraway star (statistically unlikely) or wait several years until the stars move far enough apart to see them as two separate signals instead of one. Only then can astronomers confirm each star’s physical characteristics, which they need in order to confirm the blip's nature.

Using this latter method, Virginie Batista (Astrophysics Institute of Paris) and colleagues have now confirmed a microlensing exoplanet’s existence. The team used images from the Hubble Space Telescope and the Keck II telescope on Mauna Kea to study the stars involved in the microlensing event OGLE-2005-BLG-169. A collaboration of amateur and professional astronomers discovered this system in 2005. Since then, the stars have moved farther apart in the sky; after several years, they were finally far enough apart for astronomers to tell the closer and farther star apart.

The analysis shows that the star is a K5 main-sequence star (still fusing hydrogen in its core, like the Sun), with a mass about two-thirds that of our star. It also confirms that the planet is 12 to 15 Earth masses (about Uranus’s mass) and orbits its star roughly 4 Earth-Sun distances out — that would put it on the outer edge of the main asteroid belt in our system.

This success shows that, with patience and superb images, astronomers can indeed confirm some of the microlensing exoplanet candidates.

You can read more about the result in the press release from the W. M. Keck Observatory and the Space Telescope Science Institute, or in the team’s two papers, which appear in the August 1st Astrophysical Journal. Below, you'll also find a short animation of the microlensing event (disclaimer: yeah, it's fuzzy, but the flash is neat).



Credit: NASA / ESA / D. Bennett (University of Notre Dame) / Wiggle Puppy Productions / G. Bacon (STScI)
 

References:

P. Bennett et al. “Confirmation of the Planetary Microlensing Signal and Star and Planet Mass Determinations for Event OGLE-2005-BLG-169.” Astrophysical Journal. August 1, 2015.

Batista et al. “Confirmation of the OGLE-2005-BLG-169 Planet Signature and Its Characteristics with Lens-source Proper Motion Detection.” Astrophysical Journal. August 1, 2015.

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The post Microlensing Exoplanet Confirmed appeared first on Sky & Telescope.

Categories: Astronomy

Cosmic Wind Erodes Distant Galaxy

Sky and Telescope - Sat, 01/08/2015 - 00:25

Galaxy NGC 4921 faces an intracluster wind that's eroding its star-forming terrain.

On Earth, wind can transform entire landscapes. Turns out the same is true in space.

Intracluster wind erodes the northwest corner of NGC 4921, washing away at all but the densest gas. These dense pillars stick out of a dust front that extends more than 60,000 light-years.
J. Kenney & others / Astronomical Journal

More than 1,000 galaxies swarm together in the Coma Cluster, the closest massive galaxy cluster. But it’s the intracluster medium, the gas, dust, and stars between the galaxies, that contains the bulk of the cluster’s mass (excepting dark matter). Galaxies passing through this sparse medium perceive it as a wind, and the wind reshapes the landscapes inside the galaxies.

For Coma’s biggest spiral galaxy, NGC 4921, whose gravitationally bound orbit is carrying it straight into the cluster’s center, that wind comes in from the northwest (from our perspective) and eats away at star-forming clouds of dust and gas inside the spiral.

The green contours show the neutral hydrogen reservoir superimposed on Hubble's image of the galaxy in visible light. The contours aren't circular in this face-on galaxy - they're crushed inward in the northwest corner.
J. Kenney & others / Astronomical Journal

Jeffrey Kenney (Yale University) and colleagues recently captured this wind’s erosion in Hubble Space Telescope and Very Large Array (VLA) images, as reported in the August Astronomical Journal. The VLA's observations reveal the large reservoir of neutral hydrogen gas in which NGC 4921 — like other galaxies — sits. But the hydrogen disk isn’t circular, as it would be if the face-on galaxy lived alone. Instead, it’s compressed on the northwest side, crushed inward by the intracluster wind. Hubble close-ups of the galaxy's northwestern side confirm that the wind that compresses the neutral hydrogen is also eroding all but the densest dust clouds in the spiral disk.

The Hubble Space Telescope produced these visible-light (left) and near-infrared composite images of the region in Eagle Nebula known as the Pillars of Creation. The infrared image cuts through much of the gas and reveals stars inside.
NASA / ESA / Hubble Heritage Team (STScI / AURA)

The whole northwestern structure looks very like the Eagle Nebula’s so-called Pillars of Creation (and like Bolivia’s Arbol de Piedra, a rock eroded by violent desert winds) — all three are products of erosion. But stars’ intense radiation is what eroded the gas cloud that gave us the Pillars of Creation, which are 5 light-years long. The wind-eroded pillars of NGC 4921, on the other hand, are 1,000 times larger.

Another force is likely at play in NGC 4921, too. The nearly linear dust pillars on the northwestern side are connected to a dusty front that runs about 65,000 light-years long, like an embattled line holding against the wind's onslaught. The fact that the densest globules are still connected perpendicularly to this filament, rather than breaking off like the globules in the Carina Nebula, suggests that something is helping to hold this gas together. Kenney’s team ran simulations that showed that the structures seen in NGC 4921 could only be reproduced if magnetic fields are affecting gas dynamics.

The wind faced by NGC 4921, technically known as “ram pressure,” is a force felt by most cluster galaxies, and it’s instrumental to their evolution. The wind strips away gas and dust, eventually quenching star formation and ushering galaxies from youth into old age. Just how this transformation happens still hasn’t been deciphered, but these high-resolution images will guide more detailed simulations in revealing the underlying process.

Reference:
J. Kenney et al. "Hubble Space Telescope and HI Imaging of Strong Ram Pressure Stripping in the Coma Spiral NGC 4921: Dense Cloud Decoupling and Evidence for Magnetic Binding in the ISM." Astronomical Journal. August 2015.

Celebrate 25 years of Hubble images and discoveries in our special June issue of Sky & Telescope.

The post Cosmic Wind Erodes Distant Galaxy appeared first on Sky & Telescope.

Categories: Astronomy

This Week’s Sky at a Glance, July 31 – August 8

Sky and Telescope - Fri, 31/07/2015 - 23:57

Friday, July 31

• This evening, skywatchers in the Americas see the Moon rise about a half day past when it's exactly full. Can you detect the slightest out-of-roundness in the Moon's profile yet?

• Look high above the Moon for bright Altair. Above Altair by just a finger-width at arm's length is its orange sidekick Tarazed, 3rd magnitude and far in the background.

• All month, look about 5° left of Saturn in the south-southwest after dusk for the fine telescopic double star Beta (β) Scorpii. Left or upper left of Beta by 1.6° is another fine double, Nu Scorpii (not quite bright enough to be plotted below). High power in excellent seeing may reveal Nu as the Southern Double-Double.

Saturn stays essentially fixed with respect to the stars of Libra and Scorpius this week. That's because it reaches the stationary point of its retrograde loop on August 2nd.

Saturday, August 1

• The Moon, now between Capricornus and Aquarius, is 1½ days past full (for the Americas) when it rises in evening twilight. Its slight waning gibbous phase is now more definite.

• Today is Lammas Day or Lughnasadh, one of the four traditional "cross-quarter" days midway between the solstices and equinoxes. Sort of. The actual midpoint between the June solstice and the September equinox this year comes at 8:29 a.m. August 7th Eastern Daylight Time (12:29 UT). That's the exact center of astronomical summer.

Sunday, August 2

• The tail of Scorpius is low due south right after dark. How low depends on how far north you live. Look for the two stars especially close together in the tail. These are Lambda and fainter Upsilon Scorpii, known as the Cat's Eyes. They're canted at an angle; the cat is tilting his head and winking. See the illustration above.

The Cat's Eyes point west (right) by nearly a fist-width toward Mu Scorpii, a much tighter pair known as the Little Cat's Eyes. Can you resolve Mu without using binoculars? (It's shown as single on the illustration above.)

Monday, August 3

• Altair shines high in the southeast after dark. Just above it is little orange Tarazed. A bit more than a fist-width to Altair's left, look for Delphinus, the Dolphin, leaping leftward.

Tuesday, August 4

• The red long-period variable star Chi Cygni is having a bright maximum! It was reported at magnitude 4.3 as of July 30th and may still be on the way up. See the article and comparison-star chart in the August Sky & Telescope, page 51.

Wednesday, August 5

• The Big Dipper hangs diagonally in the northwest at nightfall. Most of its stars are about 80 light-years away. Follow the curve of its handle around left by a little more than a Dipper-length and there's bright Arcturus, due west. Arcturus is the nearest orange giant, 37 light-years away.

Use binoculars during dawn these mornings to look for Mars below Castor and Pollux.

Thursday, August 6

• Last-quarter Moon (exact at 10:03 p.m. EDT). The Moon rises around midnight in Aries, far below that constellation's leading stars.

• Now that the evening is moonless, explore the telescopic sights of Scutum with Sue French's Deep-Sky Wonders column, charts, and photos in the August Sky & Telescope starting on page 54.

Friday, August 7

• The Moon, just past last quarter, rises around 1 a.m. tonight. By early dawn Saturday morning it's high in the east, forming a triangle with Aldebaran to its lower left and the Pleiades farther to its upper left.

• In early dawn these mornings, use binoculars to look for Mars below Castor and Pollux, as shown at right.

Saturday, August 8

• Seeing any early Perseid meteors yet? The Perseid shower should peak late on the night of August 12–13. The sky will be moonless.

__________________________

Want to become a better astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy.

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but it's still less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The standards are the little Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and once you know your way around, the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the beloved if dated Burnham's Celestial Handbook.

Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (meaning heavy and expensive). As Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."

This Week's Planet Roundup

Saturn as imaged by Christopher Go on July 18th. South is up. For small scopes, the most apparent feature on the globe is the contrast between the bright Equatorial Zone and the darker North Equatorial Belt.

Mercury, Venus, and Jupiter are very deep in the glow of sunset.

Mars (dim at magnitude +1.7) is just becoming visible low in the glow of dawn. Look for it a little above the east-northeast horizon 30 or 40 minutes before your local sunrise. Bring binoculars. Don't confuse it with similar-looking Pollux above it, or Castor above Pollux.

Saturn (magnitude +0.4, in Libra) shines in the south-southwest at nightfall, to the right of upper Scorpius. Fiery orange Antares, less bright, twinkles 13° to Saturn's left or lower left. Delta Scorpii is the brightest star sort of between them.

Uranus (magnitude +5.8, in Pisces) and Neptune (magnitude +7.8, in Aquarius) are in the southern sky before the beginning of dawn. Finder charts for Uranus and Neptune.

__________________________

All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.

Eastern Daylight Time (EDT) is Universal Time (UT, UTC, or GMT) minus 4 hours.

__________________________

“This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours.”

— Neil deGrasse Tyson, 2014

 

The post This Week’s Sky at a Glance, July 31 – August 8 appeared first on Sky & Telescope.

Categories: Astronomy

Tour August’s Sky: Perseids Aplenty!

Sky and Telescope - Fri, 31/07/2015 - 21:40

August provides great views of Scorpius and Saturn in the south — and the impressive Perseid meteor shower.

Look south after darkness falls, and you'll easily spot Saturn and Antares, the star marking the heart of Scorpius.
Sky & Telescope diagram

As the twilight darkens, look above the southern horizon for Saturn. It's dimmer and more subtle than brilliant Venus or Jupiter, which ruled the west after sunset earlier this year. To the lower-left of Saturn is the star Antares. It is the reddish heart of Scorpius, whose head is marked by a vertical arc of three medium-bright stars halfway between Antares and Saturn.

Meanwhile, around mid-month you’ll see many more “shooting stars” than usual, thanks to the Perseid meteor shower. This year the Perseids peak about 4 a.m. Eastern Daylight Time on August 13th. And it’s new Moon, too, so moonlight won’t spoil the view.

There's lots more to see by eye in the August evening sky. To get a personally guided tour, download our 6½-minute-long stargazing podcast below.

There's no better guide to what's going on in nighttime sky than the August issue of Sky & Telescope magazine.

The post Tour August’s Sky: Perseids Aplenty! appeared first on Sky & Telescope.

Categories: Astronomy

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