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).
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
Astronomers have expanded their ability to date stars using the stars’ own spins.
Until a few years ago, astronomers only knew the precise age of one non-cluster star that was older than a few billion years: the Sun. We date the Sun indirectly, using radioactive dating to estimate the ages of meteorites and other rocky material in the solar system. Because everything in the solar system formed around the same time, the rocks’ ages are about the same as the Sun’s.
This method doesn’t work for stars far away: astronomers had to get more inventive. They turned to star clusters. Clusters are valuable astronomical chronometers, because all stars in a particular cluster are born around the same time. Each star then evolves on a time scale determined by its mass. By comparing stars in clusters of different ages to one another, astronomers deduced which stellar properties change with age. They found that the rough difference between young and old stars of the same mass was easy to spot. Young stars in general rotate rapidly, have more spots, flare more often, and sometimes have a disk (in which planets might be forming). Old stars rotate slowly, with a much smaller fraction of spots covering their ancient “surfaces.” But refining this general relation has taken decades of work, and we hadn’t successfully applied it to cool, low-mass stars (like the Sun) older than about 1 billion years.
Now, with a new study fueled by data from NASA’s Kepler spacecraft, astronomers may have just developed a clock that is applicable to the most common type of star.
A team of astronomers led by Søren Meibom (Harvard-Smithsonian Center for Astrophysics) announced on January 5th at the winter American Astronomical Society meeting and in Nature that it has now expanded the method, called gyrochronology (or “spin-dating”), to a cluster of stars 2.5 billion years old, NGC 6819. Astronomers have had difficulty measuring the spins of older stars because they need large starspots on the stars to do it. In the youngest clusters (which are the most common), stars have stronger magnetic fields, creating large spots and frequent flaring. These magnetic fields are actually what slow the star down with time: the magnetic fields interact with the stellar winds, robbing the star of angular momentum and slowing the star down. So in older clusters, stars spin more slowly, with small spots. This makes observing rotation in the oldest stars quite challenging: astronomers need to observe the stars for a long time (the Sun, at 4½ billion years old, takes about a month to rotate once) and they also need to be precise in those observations, since smaller spots create a less noticeable dimming in the star's light as the spots transit the surface, making them more difficult to, well, spot.
Fortunately, NGC 6819 was a target of one of the most sensitive space telescopes ever produced, the Kepler spacecraft. Meibom and his team identified 30 low-mass stars in this cluster, with masses of about 1½ Suns or less, and measured their periods. While other, more massive stars are readily seen in nearby clusters, longer-living low-mass stars are challenging as they only emit a tenth (or less) of the total light of the Sun. Meibom and his team relied on the exquisite sensitivity of Kepler to detect starspots and thereby measure precise rotational periods for these low-mass stars, placing an important signpost in their behavior with time.
The team found that, at an age of 2.5 billion years, the low-mass stars seen followed a simple sequence, with more massive stars spinning faster. This suggests that at ages of greater than 2 billion years, a measurement of the rotation period of a low-mass star leads directly to its age, with a precision of about 10%.
More specifically, it supports how we think such stars spin down over time. Solar-mass stars in NGC 6819 had periods of about 18 days. When combined with the 10.8-day average spin for solar-mass stars that Meibom and others found in the 1-billion-year-old cluster NGC 6811 back in 2011, the result supports the idea that the rotational period of solar-type stars increases in proportion to the square of its age, a relation put forward by Andrew Skumanich in 1972.
Although the team’s data only extended down to about 0.85 solar mass, the NGC 6819 result may have an extremely wide range of applicability and be critically important for determining the ages of the large number of exoplanets around low-mass stars. In addition, the Large Synoptic Survey Telescope is set to begin operations around 2020 and will survey the entire night sky every three nights for 10 years. Using gyrochronology to study the stars in this data set, astronomers could unlock the ages of billions of low-mass stars in our Milky Way Galaxy, building a clear picture of how the galaxy evolved.
Reference: S. Meibom et al. "A spin-down clock for cool stars from observations
of a 2.5-billion-year-old cluster." Nature. January 5, 2015.
Amidst the release of a treasure trove of astronomical data, scientists announce the most precise “standard ruler” yet for cosmological distances.
At the winter meeting of the American Astronomical Society, astronomers released more than 100 terabytes of data as part of one of the richest databases in astronomical history. Scouring the sky since 2000, the Sloan Digital Sky Survey (SDSS) now contains 470 million stars and galaxies, a number that boggles comprehension.
A significant chunk of that data set comes from the Baryon Oscillation Spectroscopic Survey (BOSS), an SDSS survey that covered 25% of the sky over the past seven years. The goal: detect the imprint of primordial sound waves, called baryon acoustic oscillations, which directly link the universe’s infancy to its adulthood. (These are totally different from the primordial polarization imprint that’s been in the news this last year.)
BOSS adds the third dimension to 2D sky pictures by measuring spectra of 1.4 million galaxies (relatively nearby) and 300,000 quasars (relatively far away), thereby revealing the objects’ distances. That’s a monumental effort best appreciated by realizing that for every one of SDSS’s 5 million spectra, including the 1.7 million in BOSS, a man or woman hand-placed an optical fiber into a metal plate drilled with holes at that object’s location in the sky. Two people can place 1,000 fibers in 40 minutes, so placing all the fibers took 417 workdays.
In the case of BOSS, this massive effort resulted in a 3D map of the universe that covers huge volumes of space. And that’s exactly what’s required to peer into the universe’s past.The Universe: From Infancy to Adulthood
The newborn universe was a vastly different place than what we see today. Photons and ionized matter mingled together in a hot, clumpy primordial soup. The photons were trapped in the clumps — they couldn’t get far without encountering more of the dense plasma — and they exerted pressure from within. The pressure waves that rippled through the universe were akin to sound waves in Earth’s atmosphere.
The waves sloshed around for a long time, roughly 380,000. But as soon as the soup cooled enough for electrons and protons to combine, photons made their escape. With no pressure to push matter apart, gravity took over. The remnants of the primordial ripples imprinted themselves on the collapsing clumps of gas and dark matter, which would eventually become galaxies and galaxy clusters.
These remnant ripples aren’t self-evident when you look at a slice of sky. They only make themselves known in huge statistical samples by galaxies’ slight preference to lie 500 million light-years apart, instead of, say, 400 million or 600 million light-years. Yet that tiny statistical effect provides a direct link between fluctuations in the primordial soup and the cosmic web of galaxies that we see in the universe today.
BOSS surveyed huge volumes of space to see this effect, and although the final data analysis isn’t expected until later this spring, 85% of the data has already been analyzed. The primordial sound waves are detected to an extremely high precision: in technical terms, the total detection is 10 sigma. That translates as, “There’s no real question anymore about whether [these waves] exist,” says SDSS-III director Daniel Eisenstein (Harvard University).
BOSS detected ripples by looking at populations of relatively nearby galaxies, divided into two groups whose light has traveled for 3.5 billion and 5.7 billion years, respectively, and by looking at more distant quasars, whose light has traveled 11 billion years to Earth. These two data sets sandwich the era when the universe's expansion began accelerating.
Normally, astronomers need to calculate distances to these objects using their redshifts, measuring how far spectral lines shift due to the expansion of the universe. But that requires models of how fast the universe is expanding.
Primordial sound waves provide a ruler independent of cosmological models. If you know how big the ripples should be (information that can be found in cosmic microwave background fluctuations), and you measure how big they appear on the sky, you get a measure of distance. With the results announced at AAS, these distances are now known to an accuracy of 1%.
Alternatively, you can forgo the cosmic microwave background measurements and just calculate relative ripple sizes at different distances to see how quickly the ruler expands over cosmic time. Either way, both measurements provide excellent (and unsurprising) agreement with the leading cosmological model, including a mysterious dark energy whose nature has stayed constant since the Big Bang.
But perhaps the most interesting results from BOSS are yet to come, as astronomers continue to apply the enormous data set to quasar physics, galaxy evolution, and other science.
Unlike the terrestrial North Pole, the heavenly version is easily accessible any clear night of the year. We explore curiosities within one degree of the celestial north pole and take a journey back in time.
What could be more appropriate in January than a jaunt to the north celestial pole? When the polar vortex comes howling and temperatures plummet, consider a visit to the origin of all things north.
To keep things truly boreal, we're going to restrict ourselves to within one degree of the pole, or north of declination +89°. First and most obvious is the Pole Star itself — Polaris. The star's singular position at the sky's celestial pivot point has served to inflate its reputation into a common misconception. People think it's the brightest star in the sky! Yet the North Star's hardly in the running, ranking only 48th in brightness.
Because Earth's axis points squarely at Polaris, as the planet rotates the star remains almost motionless in the heavens while all the others appear to turn about it. You can easily determine the height of Polaris above the local horizon by knowing your latitude. Live in Boston, Massachusetts, at 42° north? That's how high the North Star is above the northern horizon. Any stars within 42 degrees of Polaris never set and are said to be "circumpolar." Stars beyond that limit get cut off by the horizon for a period of time before rising into view again.
Through a 2.4-inch or larger telescope, Polaris is a pleasing double star with a considerably dimmer 9th-magnitude companion. When the brighter, showier Albireo (Beta Cygnii) is visible, I enjoy showing groups this star first and then surprising them with Polaris. Many will miss the fainter companion on a quick look but then have the pleasure of discovering it themselves with just a bit of effort.
Things can be lonely at the pole, a relatively empty region of the sky, but Polaris glitters like a diamond atop a lovely asterism dubbed the "Engagment Ring," a loopy band of 9th-magnitude stellar gems plainly visible in telescopes and even in 50-mm binoculars under dark skies.
Moving deeper, we encounter a pair of deep sky objects located just 55′ from the polar pivot, the spiral galaxy NGC 3172 and MCG +15-1-10. Also called Polarissima Borealis because of its proximity to the north celestial pole, NGC 3712 glows feebly at magnitude 13.6 and will prove a challenge for a 10-inch telescope under dark skies. In my 15-inch Obsession it's a dim, round patch with a brighter center. For those who like their fuzzies faint, try spotting its 15th-magnitude neighbor about 2′ to the west.
One of the bonuses of observing objects near the celestial pole is not having to worry about tracking your target. An object centered in the field of view will stay there for many minutes without the need to nudge the telescope — a real pleasure for those with non-motorized Dobsonian reflecting telescopes.
The closest "bright" star to the north celestial pole is 9.7 magnitude SAO 3788, presently about 15′ (1/4°) away. Due to the precession of Earth's axis, Polaris has only been close enough to assume the role of pole star since the early medieval days. Around the time of Caesar, both it and Kochab, an equally bright star in the Little Dipper's bucket, were nearly equidistant from the pole.
Polaris has been inching poleward for centuries and will reach a minimum distance of 27′ — just under 1/2° or one Full Moon diameter — in March 2100. The news will undoubtedly be a hot topic on what remains of the Internet in that distant year. Will someone scheme up a doomsday scenario where the pole star focuses magnetic beams on a hapless humanity? Don't doubt it.
Long before the reign of Polaris, when the Great Pyramid was built in Giza around 2550 BC, 3.6-magnitude Thuban (Alpha Draconis) marked the polar point. At magnitude 2.0, Polaris has been the brightest pole star since 12,000 BC when Vega last had a run at it. Once Polaris begins its slow departure in 2100, it won't return again to polar glory until AD 28,000!
Can't find the pole star? Let a Sky & Telescope Star Wheel guide you!
Alan MacRobert, Senior Editor, Sky & Telescope
617-864-7360 x2151, amacrobert@SkyandTelescope.com
Kelly Beatty, Senior Contributing Editor, Sky & Telescope
617-864-7360 x2168, kbeatty@SkyandTelescope.com
Comet Lovejoy, already being tracked by backyard astronomers worldwide, is entering its best and brightest two weeks for viewing. From about January 7th through 24th the comet is predicted to be glowing at 4th magnitude — bright enough that skywatchers with clear, dark skies might be able to just glimpse it by eye, without optical aid. And the early-evening sky during this time will be dark and moonless, allowing the best views.
On January 7th, Comet Lovejoy passes closest by Earth at a distance of 44 million miles (70 million km), nearly half the distance from Earth to the Sun. But its distance will change only a little for many nights after that, so you'll have plenty of opportunities to track it down.
"If you can find Orion shining high in the southeast after dinnertime," says Sky & Telescope senior editor J. Kelly Beatty, "you'll be looking in the right direction to track down Comet Lovejoy." From there, use Sky & Telescope's sky maps (see below) to find the right spot for each date.
To the unaided eye, Comet Lovejoy might be dimly visible as a tiny circular smudge under dark-sky conditions. Through binoculars or a wide-field telescope, it will be more obvious as a softly glowing ball. Light pollution will make it less apparent.
During the next two weeks, the comet crosses the constellations Taurus, Aries, and Triangulum, climbing higher and higher in early evening. It passes 10° to the right (west) of the Pleiades star cluster on the evenings of January 15th through 17th. Although by then Comet Lovejoy will be receding from Earth, it doesn't come closest to the Sun until January 30th, at a rather distant 120 million miles (193 million km). By that date moonlight will begin to interfere, and the comet should be starting to fade as seen from Earth's point of view.
This is the fifth comet discovery by Australian amateur astronomer Terry Lovejoy, and he found it in images taken with his backyard 8-inch telescope. It's a very long-period comet, meaning that it has passed through the inner solar system before, roughly 11,500 years ago. Slight gravitational perturbations by the planets will alter the orbit a bit, so that the comet will next return in about 8,000 years. Astronomers have given it the official designation C/2014 Q2.Hints of Green and Gold
Based on its steady, uninterrupted brightening, observers estimate that the comet's solid, ice-rich nucleus is at least 2 or 3 miles across, slightly larger than typical. But the glowing object we actually see is vastly larger and less substantial. The comet's visible head, or coma, is a cloud of gas and dust roughly 400,000 miles across, that has been driven off the nucleus by the warmth of sunlight.
Human eyes can't perceive color in dim nighttime objects well, but photographs show that Comet Lovejoy has a lovely green hue. The green glow comes from molecules of diatomic carbon (C2) in the coma that fluoresce in response to ultraviolet sunlight. By contrast, Comet Lovejoy's long, delicate gas tail is tinted blue, thanks to carbon monoxide ions (CO+) that are likewise fluorescing.
In addition, dust in a comet's coma and tail simply reflects sunlight, so dust features appear pale yellowish white. The most memorable comets tend to have dramatic dust tails, such as spectacular Comet Hale-Bopp in 1997 and another discovery by Lovejoy, C/2011 W3, in 2011.
The current Comet Lovejoy is not producing enough dust to create a bright tail - and in fact this interloper wasn't expected to become so obvious at all. But by late 2014 amateur astronomers had noticed that the comet was brightening steadily and faster than predicted.
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The Hubble Space Telescope has turned its ultraviolet, visible-light, and near-infrared eyes to the queen of galaxies, M31, capturing the biggest and sharpest image yet of our neighbor.
At the winter American Astronomical Society meeting this week in Seattle, a poster of the Andromeda Galaxy welcomes astronomers to the biggest astronomy conference of the year. The poster is something like 10 feet tall and 25 feet wide — and that doesn’t even do the image justice.
The Hubble Space Telescope high-res image above captures a slice of Andromeda spanning 48,000 light-years, from bulge to outskirts. Its 1.5 billion pixels would need 600 HD television screens to display to full effect.
Hubble began studying Andromeda in December 2011 as part of the Panchromatic Hubble Andromeda Treasury (PHAT) project led by Julianne Dalcanton (University of Washington). The imaging project finished in November 2013, and the team released the result on January 5th at the meeting. The final image includes 12,834 shots from more than 400 pointings taken through ultraviolet, optical, and near-infrared filters. (The photo above shows only the visible-light view through the blue and red filters, a mosaic of roughly 3,700 optical images).
Enlisting the help of well-known astrophotographer Robert Gendler, the team then stitched the images together to create the seamless mosaic. The stitching is so careful that the mosaic is aligned at the level of individual stars — roughly 117 million of them — or to better than one-tenth of an arcsecond. That’s not too shabby for charting a galaxy 2.5 million light-years away.
The result is a detailed look at our neighbor like we’ve never seen before, one best explored via the zoom tool on the European Space Agency’s Hubble site. (It takes a while to load, but it’s worth it.) Explore (and zoom, and zoom some more!) and you’ll see those 117 million stars, along with a couple thousand star clusters and star-forming regions as well as dark, twisted silhouettes traced by complex dust structures.The Science Behind the Pretty Picture
For Dalcanton, it’s the last item in that list — the twisted columns of obscuring gas and dust — that’s most interesting. Dalcanton has already used the image to map dust across the Andromeda Galaxy.
The team first divided the image into boxes 5 arcseconds (65 light-years) wide, each one containing foreground stars, background stars, and dust. As background starlight passes through intervening dust, it reddens just as a sunset reddens when passing through dust or smog. So for each box, Dalcanton’s team modeled the stars’ range of brightnesses and colors, and for each box they included two populations in their model: one reddened and one unreddened.
The result: a 3D dust map of the galaxy, one that has more than four times better resolution than previous dust-mapping methods. The team had to "fuzzify" the new dust map in order to compare it against other methods, but so far it’s in excellent agreement with previous charts in terms of the dusty structures’ shapes.
But surprisingly, the team found that other widely used dust maps actually predict twice as much dust as is really there. Dalcanton suggests a calibration issue with the other model as the most likely culprit. If that’s the case, nearby galaxies may have much less dust than previously thought.
Charting dust and its mysteries is essential to understanding starbirth, as dust helps to cool interstellar gas, and stars form from cool gas. This study is only the first from PHAT to aim for that ultimate charting goal. Forthcoming studies will study star formation as a function of position in the galaxy, investigate the galaxy’s star-formation history, and much more: “This is meant to be a legacy data set, to be used for decades,” Dalcanton says.The Mystery Ring
Another surprise from the PHAT mapping is in the Andromeda Galaxy’s structure. Observations such as those in ultraviolet from NASA’s GALEX spacecraft and in infrared from the Spitzer Space Telescope reveal where stars are currently forming in the Andromeda Galaxy. As expected, star-forming regions riddled with young, massive stars trace out M31’s iconic spiral arms. The tightly wound arms — perhaps in some cases even genuine rings, like those created in a stone-disturbed pond — are likely a transient thing; computer simulations show that such arms should move and evolve over time.
GALEX and Spitzer images show the lay of the stellar land “now” (well, when light left the galaxy 2.5 million years ago). But because the color and luminosity of stellar populations reveal the stars’ ages, and because these properties change as you look at different parts of the galaxy, the PHAT images actually enable astronomers to look back in time and determine M31’s star-forming history in various locations.
What the team found is that the arms aren’t all as transitory as expected: a ring present today was also forming stars between 500 and 630 million years ago, a time scale much longer than astronomers predicted for these structures to survive. The inner and outer rings vary as expected, but not this one.
“This was really a surprise,” Dalcanton said in a press conference. In terms of stellar content, the density of stars in this ring is about 40% higher than in other regions in Andromeda, and it contains both old and young stars — it’s not just the young stars tracing it out, as is common with spiral structure. “So it’s this long-lived dynamical thing that’s just kind of sitting there, for reasons we don’t understand.”
At least, not yet.
Learn more about the team’s results on the PHAT project website.
Science Editor Camille M. Carlisle contributed to the reporting and writing of this news blog.
The post Comparison of angular diameter of the Sun and Moon appeared first on Sky & Telescope.
The editors of Sky & Telescope make every effort to provide accurate information, but errors do sometimes slip through. We correct all mistakes online as well as printing corrections in the magazine. So if you see something questionable in the magazine, check SkyandTelescope.com/Errata to see if it's a known problem.
Tony FlandersThis article lists all known errors in issues of Sky & Telescope for 2015. See also the errata for 2014.
Page 33: The Atmospheric Dispersion Corrector shown is manufactured by Astro Systems Holland, not Pierro-Astro, and is available at www.astrosystems.nl.
Page 45: In the Binocular Highlights finder chart, the star Atlas is incorrectly labeled as Alcyone.
Page 56: In the Deep-Sky Wonders column, Abell 24 is incorrectly placed north of Zeta Canis Majoris; it is north of Zeta Canis Minoris.
Page 57: Download an updated version of the "Objects in Canis Major and Canis Minor" table.
Page 58: Douglas’s Triangle is not the three stars in the middle of the image but the three stars that combine to create the top “star” in that triangle. A zoomed-in image appears below. A finder chart is available for download.
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