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 are tracking down the seeds that likely grew to become today’s most massive elliptical galaxies.
Astronomers like galactic runts. It’s not that they’re cute — although the Large Magellanic Cloud is vaguely reminiscent of a fuzzy caterpillar. It’s that runts were likely the building blocks of the big galaxies we see today.
The largest, most massive galaxies in the local universe are ellipticals, big golden clouds of stars that have burned through their star-forming gas reservoirs and now sit “quiescent,” enjoying old age. But about a decade ago, astronomers looking into the early universe discovered that quiescent galaxies 10 or 11 billion years ago were actually the smallest galaxies around, roughly one-tenth the size of today’s ellipticals and one-third (or less) that of the other star-forming galaxies at that epoch.
Even so, the compact galaxies were massive: in stars they can outweigh the Milky Way, even though they’re on the order of one-tenth the size.
These compact quiescents likely grew into the red-and-dead behemoths of today. Three lines of evidence point to that interpretation, explains Guillermo Barro (University of California, Santa Cruz). One, there are very few compact quiescent galaxies today, so they must have disappeared somewhere. Two, the density of stars in these ancient, compact galaxies is similar to that in the cores of local, big ellipticals. And three, if the compact galaxies grew by merging with less massive companions (probable), the mergers would have preferentially built up the galaxies’ outer edges, leaving the core more or less unchanged (explaining #2).
. . . But where did the cores come from?
Astronomers potentially found an answer to that question in the last year or so when they discovered compact, star-forming galaxies that existed around 11 billion years ago (a.k.a. at a redshift of about 2). These star-forming galaxies had sizes and masses similar to the compact, quiescent galaxies.
Now, two teams have confirmed that the velocity of gas moving around inside several of these small star-forming galaxies matches the velocities of stars in the small quiescent ones. It’s this gas that forms stars, so if the dynamics of the gas match the dynamics of the stars, that’s a pretty good indicator that we’re looking at the same type of beast at different ages.
Both Barro and his colleagues and an independent team comprising Erica Nelson (Yale) and her colleagues came to this conclusion using multiwavelength data for compact galaxies found in the GOODS and COSMOS surveys. These objects all have redshifts between 1.97 and 2.49, meaning they existed right at the time the transition seems to have happened. They also have stellar masses ranging from 40 billion to 200 billion Suns. (The Milky Way has a total stellar mass at the lower end of this range.)
Assuming the gas motions calculated are for gas that’s settled into these compact galaxies and isn’t infalling or outflowing (and the teams are pretty sure that’s true), and assuming no more gas will dump down onto these cores, star formation will burn through the available gas in a few hundred million years. Feedback from gas-guzzling, jet-spewing supermassive black holes might exacerbate the quick death by removing gas, too. Barro’s team found X-ray evidence for an active galactic nucleus (AGN) in 7 of the 13 galaxies it studied, while Nelson’s team saw no sign of an AGN in the galaxy it analyzed.
This timeline puts the compact, star-forming galaxies right on track to become the small, quiescent galaxies observed. They’ll probably all be “dead” in 1 to 2 billion years, or at a redshift of 1.5 or so. Afterwards, they will (we think) build up their outer edges to become today’s massive ellipticals.
This all works very nicely. But it does raise a big-picture question. Last year Nelson and other members of her team observed the growth of less massive, disk galaxies (similar to the Milky Way) between 7.5 and 11 billion years ago. The observations showed that such galaxies built up both their core bulges and their disks at the same time. But the new results confirm that more massive, elliptical galaxies likely grew from the inside out. Why the difference? Perhaps because ellipticals tend to grow in denser parts of the universe (true); perhaps because the universe itself was denser billions of years ago (also true). Or perhaps there’s something else going on.
G. Barro et al. “Keck-I MOSFIRE Spectroscopy of Compact Star-forming Galaxies at z>2: High Velocity Dispersions in Progenitors of Compact Quiescent Galaxies.” arXiv.org. Posted May 27, 2014.
E. Nelson et al. “A Massive Galaxy in its Core Formation Phase Three Billion Years after the Big Bang.” Nature. August 27, 2014.
Find galaxies for yourself using our latest e-book, Summer Deep Sky.
Friday, August 29
The Moon is coming back into the evening sky. Look for the waxing crescent low in the west-southwest in twilight, as shown at lower right. Can you make out Spica twinkling beneath it? Binoculars help. Far to their upper left are Saturn and Mars.
Saturday, August 30
The waxing crescent Moon now shines closer to Saturn and Mars, as shown above. Can you see little Alpha Librae in the middle of the narrow triangle they make?
Sunday, August 31
Spot the Moon at dusk with Saturn to its right and Mars to its lower left (for North America).
As the stars come out this week, the first you see may be Arcturus shining high in the west. As the sky gets a little darker, look to its right for the Big Dipper scooping down in the northwest.
Monday, September 1
First-quarter Moon this evening and Tuesday evening (exactly first quarter at 7:11 a.m. Eastern Daylight Time Tuesday morning). It's passing over Scorpius, as shown above.
Tuesday, September 2
The Great Square of Pegasus is well up in the east as soon as nightfall is complete. It's larger than your fist at arm's length and currently stands on one corner. Seen from your latitude at your time, how close is its balance to being perfect?
Wednesday, September 3
Look lower left of the Moon right after nightfall for the Teapot of Sagittarius, tilting and pouring to the right.
Thursday, September 4
In Friday's dawn, use binoculars to help pick up Venus just above the eastern horizon about 30 minutes before sunrise. It's far to the lower left of Jupiter. Can you make out Regulus, less than a hundredth as bright, within 1° of Venus?
Friday, September 5
Saturn, Mars, Delta (δ) Scorpii, and Antares form an equally-spaced ragged line in the southwest at dusk, as shown at right. Delta Scorpii used to be a bit dimmer than Beta above it. Then in July 2000 it doubled in brightness. It has remained bright, with fluctuations, ever since.
Look high above the Moon this evening for Altair.
Saturday, September 6
This evening look to the right of the Moon, by a little more than a fist-width at arm's length, for two faintish (3rd-magnitude) stars: Alpha and Beta Capricorni, one above the other. Alpha is the one on top. With sharp vision, you can barely see that it's double. Binoculars resolve it easily.
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. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).
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 (able to point with better than 0.2° repeatability, which means fairly 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
Mercury (about magnitude –0.2) remains quite deep in the sunset, as it always does during its evening apparitions that happen in late summer and early fall. Scan for Mercury with binoculars just above the horizon due west about 20 minutes after sundown.
Venus (magnitude –3.9) and Jupiter (magnitude –1.8) shine in the east-northeast during dawn. Jupiter is the higher and easier one to spot. Watch far to its lower left for Venus rising as dawn grows bright. The two planets continue drawing farther apart: from 12° apart on August 30th to 20° by September 5th. Jupiter is moving higher, and Venus is gradually sinking lower.
Use binoculars to catch Regulus less than 1° to Venus's lower left on the morning of September 5th (for North America).
Mars and Saturn, both magnitude +0.6, glow in the southwest at dusk, moving apart after their conjunction last week. They're 4° apart on August 29th and 7° by September 5th. Mars is the one on the lower left early in the week, directly left later. Off to their left are fainter Delta Scorpii, then Antares. Compare all their colors.
Uranus (magnitude 5.7, in Pisces) and Neptune (magnitude 7.8, in Aquarius) are high in the southeast and south, respectively, by midnight. See our Finder charts for Uranus and Neptune online or in the September Sky & Telescope, page 50.
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.
"The universe is full of magical things patiently waiting for our wits to grow sharper."
— Eden Phillpotts, "A Shadow Passes," 1918
The post This Week’s Sky at a Glance, August 29 – September 6 appeared first on Sky & Telescope.
A new measurement, made using radio interferometry, argues that the distance to the Pleiades star cluster measured by ESA's Hipparcos satellite is decidedly wrong — and that ground-based astronomers had it right all along.
Last week I spent some blissful nights observing from rural Maine under pristine skies. In the wee hours I could see that familiar celestial landmark, the Pleiades star cluster, rising in the northeast over a stand of pine trees. They looked so delicate and serene — hardly the subject of a controversy that has nagged at astronomers for 1½ decades.
Open star clusters like the Pleiades and Hyades are perfect proving grounds for models of stellar evolution because their stars all have the same age and composition yet exhibit a wide range of masses. But for these models to work, it's critical that astronomers know the clusters' distances precisely.
Enter Hipparcos, a small orbiting observatory launched by the European Space Agency in 1989. Its name is both an acronym for High-Precision Parallax Collecting Satellite and a namesake for the ancient Greek astronomer/mathematician Hipparchus of Rhodes.
To gauge the distances of stars, Hipparcos used a technique already familiar to astronomers: trigonometric parallax. The spacecraft measured the position of roughly 120,000 nearby stars from various points along Earth's orbit to within about 0.001 arcsecond. Far more precise than possible with ground-based telescopes, these measurement sets revealed tiny shifts of nearby stars against the background of more distant ones. A star that's 1 parsec (3.26 light-years) away exhibits a positional shift of 1 arcsecond over a baseline of 1 astronomical unit (the mean Earth-Sun distance).
So, in principle, Hipparcos should have provided accurate parallaxes to stars up to many hundreds of light-years away, easily refining the distances to nearby open clusters such as the Pleiades (Messier 45) and Hyades clusters in Taurus, the Beehive (Messier 44) in Cancer, and the Alpha Persei Cluster.
Eager astronomers jumped at the mission's results when released in 1997, but the "Pleiades problem" arose almost immediately. As detailed in a pair of articles here and here, ground-based methods had consistently shown that the Pleiades lie about 435 light-years (133 parsecs) away. However, according to Hipparcos, the cluster has a distance of just 392 light-years (120.2 parsecs), supposedly with an error of less than 1%.
If the cluster really was 10% closer than everyone had thought, then its stars must be intrinsically dimmer than stellar models suggested. A debate ensued about whether the models or the spacecraft data were wrong. Much hung in the balance, but the discrepancy remained unresolved. The Pleiades problem remained a major embarrassment among astrometrists worldwide.A New and Better Yardstick
Now Carl Melis (University of California, San Diego) and others have seemingly put the matter to rest. In the August 29th issue of Science, they report distance results derived with a different and powerful method: very-long-baseline radio interferometry. They have seemingly nailed the distance at 444.0 light-years (136.2 parsecs), likewise accurate to within 1%.
The distance found by Melis's team agrees well with previous ground-based determinations — and not with Hipparcos. If this result holds up, it’s good news for the standard models of how stars work. But astronomers must try to understand why the Hipparcos observations misjudged the distance so obviously — and whether its entire database of stellar distances is suspect.
There's some suspicion that mission scientists failed to notice systematic positional errors during the processing of the Hipparcos data, but no one has yet turned up evidence for that. In any case, the mission team for Gaia, ESA's much more accurate follow-on astrometry mission, are taking special care.
In fact, as Léo Girardi (Padova Astronomical Observatory) points out in an accompanying Science perspective, by 2020 Gaia data should completely resolve any lingering aspects of the puzzling Hipparcos discrepancy. Perhaps there really were errors in the Pleiades distance determination — or, conceivably, the cluster's stars could be quite spread out along our line of sight.
Find the Pleiades and Hyades in Taurus, along with thousands of other stars and deep-sky objects, with Sky & Telescope's Pocket Sky Atlas.
With a subtle beauty all its own, the earthshine we see glowing in the lunar night invites us to consider Earth's many connections to the Moon
This week's crescent Moon offers more than two horns to hang your hat on. Take a close look, and you'll see an entire circle of moonlight. Sunlight illuminates the bright crescent, but the remainder of the disk would be utterly black and invisible were it not for earthshine.
Often referred to as the "ashen light" or "the old Moon in the New Moon's arms," earthshine begins it lunar journey literally at your doorstep.
Sunlight reflected from our planet radiates into space. A portion of it passes the Moon, strikes the lunar surface, and reflects back to our eyes. Much of that light is absorbed by the charcoal-dark lunar soil, which is why the earthlit Moon appears faint. From the surface of the Moon, ground illumination would resemble deep twilight here on Earth. By comparison, the bright crescent is illuminated by direct sunlight.
As the Moon waxes in phase, sunlight crawls across more and more of the darkened lunar landscape in our view. At full Moon, the entire Earth-facing side of our satellite is basking by sunlight. During the Moon's waning phases, earthlight increases as sunlight withdraws.
Because the Moon and Earth's phases are complementary, Earth's phase (as seen from the Moon) always corresponds to the portion of the Moon that we see illuminated by earthshine. So earthshine is brightest when the lunar crescent is skinniest, in the days just after or before new Moon.
Think the "Supermoon" is a big deal? An astronaut looking back at a "full Earth" would see an orb nearly four times the full Moon's apparent diameter and 50 times brighter!
This immediately suggests a challenge. How long can you keep earthshine in view? By the time the waxing crescent Moon is 4 days old, Earth's in gibbous phase (from a lunar perspective) and fading. At first quarter, a "half-Earth" lights the lunar sky and then dwindles to a crescent around the time of Full Moon.
You should be able to follow earthshine up to 5 days past new with the unaided eye and a few days beyond that when viewing through binoculars or a telescope. As the Moon waxes, not only is the Earth getting dimmer from a lunar perspective, but the area lit by our planet is also shrinking. My personal record is 9 days past new with a 10-inch telescope. I bet you can beat it. Hint: Keep the sunlit portion of the Moon out of the field of view.Sightseeing in the Lunar Darkness
One of the lesser appreciated aspects of lunar observing is exploring the dusky moonscape with binoculars or a telescope. There's much to see. Binoculars show a half dozen or more lunar seas, and the bright-rayed crater Tycho is an easy catch. Through a telescope you'll feel like you're hunting creatures that only come out after dark. Try it sometime for a whole new perspective.
While you can see earthshine anytime a crescent is present, northern hemisphere observers see it best in autumn morning twilight or spring evening twilight, because the lunar crescent stands high in the sky. Spring is also when earthshine is intrinsically brightest according to the Project Earthshine study conducted by Big Bear Solar Observatory and the California Institute of Technology.
Because the brightness of earthshine depends primarily on Earth's cloud cover, variations in its intensity can help us understand changes in our planet's climate. The study indicates a possible drop in Earth's overall reflectivity between 1994 and 1998, followed by a distinct jump (about 0.5%) from late 1998 through mid-2000. These changes might be correlated with the rise solar maximum, but the Sun's output varies by only about 0.1% during its 11-year-long activity cycle. A related paper describes day-to-day changes in brightness (about 5%) due to large-scale weather changes. Amazing stuff!
Earth and Moon share ancient ties. According to prevailing theory, the Moon originated in a catastrophic collision between a Mars-sized planet and the infant Earth 4.5 billion years ago. Chunks of our planet's crust were blasted into orbit and later coalesced as our one and only natural satellite. Seeing Earth's reflection as we hold the Moon in our gaze reminds us of the deep connections between our two worlds.
The Milky Way and Andromeda galaxies dominate the small neighborhood of galaxies they live in, a cluster called the Local Group. But how do they stack up with each other? Astronomer Michael Rich takes us on a fantastical exploration of these two giant spirals, showing us how they compare in terms of size, mass, star-formation rate, and a host of other factors. Closer to home, an endeavor called the Library Telescope Program has brought dozens of telescopes to public libraries, allowing anyone to check one out and discover the universe for themselves. Also in this issue, you can read about the discovery of radio emission from the Sun, how to observe stars and planets in broad daylight (yes, you can!), and how to fight image artifacts in your astrophotography.Feature Articles
Battle of the Titans: The Milky Way vs. Andromeda
The Milky Way and Andromeda galaxies vie for Local Group supremacy.
By Michael Rich
Discovering the Radio Sun
The wartime discovery of radio emissions from the Sun gave birth to the field of solar radio astronomy.
By J. Kelly Smith & David L. Smith
Stars & Planets in Broad Daylight
You don’t need to stop observing just because the Sun is above the horizon.
By Chris Dalla Piazza
Check Out This Telescope!
An innovative program allows newcomers of all ages to borrow compact, high-quality reflectors from public libraries.
By John Jardine Goss
Eliminating Band & Line Noise
Here’s a technique that removes common artifacts from DSLR and CCD images.
By Michael Unsold
Obit: Bill Bradfield by Roger W. Sinnott
The amateur astronomer from Australia used an unconventional telescope to find his comets.
See Both the Sun and Eclipsed Moon by John Rao
During the October 8th lunar eclipse, you can see the Sun and the eclipsed Moon simultaneously.
A Comet Cruises By
Comet Siding Spring flies by Mars on October 19th.
Lunar Librations by Sean Walker
Librations and other lunar data for October 2014.
Darkness and Light
Cygnus is replete with wonders, both bright and dark.
By Sue French
Table of Contents
See what else October's issue has to offer.
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