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
Nova in Sagittarius reaches magnitude 4.9. A classical nova that leaped up to 6th magnitude on March 15th in the Sagittarius Teapot continued to brighten to about magnitude 4.8 as of March 20th. Sagittarius is low in the south-southeast before the first light of dawn (seen from mid-northern latitudes). Article, charts: Nova in Sagittarius Brightens!.
Friday, March 20
The Sun underwent a total eclipse for parts of the North Atlantic and Arctic Ocean earlier today. The partial phases swept across all of Europe, North Africa, and central Asia. Lots of news coverage.
As dusk turns to night, spot Venus still shining in the west. To its upper right by about a fist at arm's length, look for 2.0-magnitude Hamal, the brightest star of Aries. Farther to Venus's upper left or left, look for 2.5-magnitude Menkar, Alpha Ceti.
Spring begins in the Northern Hemisphere at the equinox, 6:45 p.m. EDT (3:45 p.m. PDT). This is when the Sun crosses the equator heading north for the season.
The word "equinox" comes from night and day supposedly being equal on this date, but that's not really true. It would be true if Earth had no atmosphere and the Sun were a point rather than a disk. But with an atmosphere, daylight continues long after the moment of sunset. Second, sunrise and sunset are counted not from when the Sun's center is on the true horizon, but when its top edge is on the horizon; this adds a couple minutes to daytime. And third, atmospheric refraction at the horizon elevates the Sun by about its own apparent diameter, adding a few more minutes before sunset time.
Saturday, March 21
In twilight, look west well below Venus for a very thin waxing crescent Moon close to Mars, as shown here. The Moon is just one day old; new Moon was marked by yesterday's solar eclipse.
We see the Moon's night side (dimly earthlit), and just a little of the sunlit side around the edge, because the Moon is still nearly along our line of sight to the Sun. Faraway Mars shows us mostly its day side, because it's nearly on the same line of sight on the far side of the Sun.
Sunday, March 22
Crescent Moon and Venus. Look west in twilight for the waxing crescent now posing with Venus, as shown here. At the times of twilight for North America, Venus is 3° or 4° to the Moon's right. Although they look close together, Venus is currently 520 times farther away.
Monday, March 23
Venus shines well to the Moon's lower right this evening.
Venus is brightest point of light at dusk. The second-brightest is Jupiter, much higher in the southeast. Look to the right of Jupiter by two or three fists at arm's length for Procyon; look the same distance lower right from Procyon, and there's the evening's third-brightest point, Sirius.
Tuesday, March 24
The Moon shines amid the big, loose Hyades cluster for the Americas. The Moon occults Aldebaran for Alaska and northwestern Canada; see map and timetables of Aldebaran's disappearance and reappearance.
Wednesday, March 25
Look well to the left of the Moon this evening for Betelgeuse in the top of declining Orion. Look lower right of the Moon for similarly-colored Aldebaran, not quite as bright, in Taurus.
Thursday, March 26
The first-quarter Moon shines above Orion and below Gemini this evening. If you have a dark enough sky (or binoculars), you can see that the Moon is in or near Orion's dim, upraised club.
Friday, March 27
This evening the Moon forms a big kite shape with bright Jupiter far to its left, Pollux to the Moon's upper left, and Procyon to its lower left.
Saturday, March 28
Now the Moon shines inside the triangle of Jupiter, Pollux, and Procyon.
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 is hidden deep in the glow of sunrise.
Venus (magnitude –4.0) blazes in the west during and after evening twilight as the unmistakable "Evening Star."
Mars is magnitude +1.3, less than 1% as bright as Venus. It's gradually sinking ever farther below or lower right of Venus — from 12° below it on March 20th to 15° below on the 27th.
Jupiter (magnitude –2.4, in Cancer) shines high in the southeast as the stars come out. It's the brightest point of light on that side of the sky. It passes highest in the south around 10 p.m. daylight-saving time.
In a telescope Jupiter is still 43 or 42 arcseconds wide. Don't expect to see nearly the amount of detail with your eye that sophisticated video-frame stacking with a large amateur telescope can bring out, such as in the fine image here!
Saturn (magnitude +0.3, at the head of Scorpius) rises around midnight daylight-saving time. It's highest in the south just before dawn begins. Below or lower left of Saturn by 8° is orange Antares, the Scorpion's heart.
Look just ½° below Saturn before dawn for Nu Scorpii, a showpiece double star for telescopes. And less than 2° to their right is Beta Scorpii, an even finer telescopic double.
Uranus and Neptune are hidden behind the glare of the Sun.
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.
Astronomers have found a set of possible dwarf galaxies near our galaxy, a discovery crucial to understanding dark matter.
Two independent teams of astronomers went panning for gold in the Southern Hemisphere sky — and they struck it rich. Between the two, the teams discovered nine possible dwarf galaxies near the Milky Way, nuggets that may pave the way for a better understanding of dark matter in our local universe.
The candidates are not yet confirmed dwarfs. Future observations will determine whether these are really dwarf galaxies or, the most likely alternative, crowded stellar cities known as globular clusters.
Keith Bechtol (University of Chicago) led a team with the Dark Energy Survey (DES), an optical and near-infrared project conducted with the 4-meter Victor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile. Combing through the first year of images taken by the Dark Energy Camera, they came upon eight clusters of stars well outside the boundaries of the Milky Way.
A second team, led by Sergey Koposov (University of Cambridge, UK), found the same eight dwarf candidates, plus one more, in the same DES data. The ninth lies near the edge of a gap in the detector, which makes measurements of its stars’ brightnesses and colors tricky.
The dwarf candidates range in size from a mere 120 light-years to 1,300 light-years across. The nearest, Reticulum 2 at a distance of almost 100,000 light-years, is the strongest candidate. Even though it’s small (200 light-years across), it’s elongated, so it’s less likely to be a globular cluster posing as a dwarf galaxy. The second most-likely dwarf galaxy, Eridanus 2, is also stretched out and lies the farthest away at a whopping distance of 1.2 million light-years.
Both teams used different methods to search survey data for “overdensities” of stars — i.e., stellar clusters. So until future observations can be obtained, it’s still possible that some of these candidates might be globular clusters instead.
“The only true confirmation that these objects are galaxies rather than globular clusters comes from measuring their total mass,” says Bechtol’s coauthor Alex Drlica-Wagner (Fermi National Accelerator Laboratory). “Unlike globular clusters, most of the mass of galaxies resides not in their stars but in the dark matter that surrounds them."
The best way to measure the mass, Drlica-Wagner says, will be to collect spectra and measure the velocities of the stars with respect to one another. “For faint systems like those that we recently discovered, we will require some of the largest telescopes in the world to get accurate velocity measurements,” he adds.
Koposov’s team is similarly planning follow-up, including observations with the Hubble Space Telescope.
The spectra will also tell astronomers about the bulk motions of the stars — that is, their collective motion either towards or away from the Milky Way — which will reveal whether these potential dwarfs are in fact satellites of our galaxy.Dwarf Galaxies and Dark Matter
Dwarf galaxies might hold the key to understanding the nature of dark matter. But only time will tell what, if anything, these new dwarf candidates will reveal.
Since the Fermi Gamma-Ray Space Telescope was launched in 2008, it has searched the skies for the signature of annihilating dark matter particles. This signature might be expected if dark matter consists of weakly interacting massive particles, or WIMPs. When two WIMPs meet, the standard theory goes, they produce less exotic (and more detectable) particles, as well as showers of gamma rays.
Dwarf galaxies are a great place to look for an annihilation signal because there’s not much going on — they’re less likely to host other gamma-ray sources such as black holes or pulsars. They also can have a large amount of dark matter compared with their mass in stars and gas.
So eyebrows went up when Alex Geringer-Sameth (Carnegie Mellon University) and colleagues released a paper on the arXiv on March 8th announcing a 3.7-sigma detection of gamma rays from Reticulum 2 (the nearest and strongest of the dwarf galaxy candidates). In particle-physics world, a 3.7-sigma result is considered “evidence” that’s worth following up but not “discovery,” says Fermi team member Andrea Albert (SLAC National Accelerator Laboratory).
As exciting as it would be, that evidence isn’t holding up under scrutiny. A recent publication from the Fermi collaboration uses a more sensitive (and not-yet-public) data set to investigate 15 nearby dwarf galaxies. Even though the Fermi team detected gamma-ray emissions from Reticulum 2 (at the 1.5-sigma level), there’s a 13% chance that the detection isn’t real.
“Having the significance go down like that with a more sensitive data set usually indicates a statistical fluke,” Albert says. So the gamma-ray excess seen by Geringer-Sameth’s team (which includes Koposov) is more likely a bump in a noisy background.
In fact, the Fermi team’s measurements of 15 dwarf galaxies rules out annihilation from WIMPs with masses less than 100 billion electron volts — if WIMPs do exist, they’d have to be massive indeed. (Planck satellite measurements of the cosmic microwave background place less stringent limits, ruling out only WIMPs below 20 billion electron volts.)
“In the past few years we have just started to scratch the surface,” Albert adds. WIMPs could exist at much higher masses, say 500 GeV, or perhaps even out of Fermi’s range altogether, she explains. “I'm not ready to throw in the towel.”
The post Postcard from Walter Scott Houston to me, Nov 1978 appeared first on Sky & Telescope.
As the countdown for Friday's total solar eclipse nears zero, "umbraphiles" from around the world are flocking to remote parts of the far north in the hope of finding clear skies.
Total eclipses of the Sun occur about every 1½ years on average, and there are roughly a thousand people worldwide who make a point to see as many of them as they reasonably can.
"Reasonably" is the key here. The one in February 1998 was easy, as the Moon's shadow passed right over Aruba and drew an armada of cruise ships to the Caribbean (rum punch, anyone?). The 2016 eclipse will take umbraphiles to balmy Indonesian seas. And looking ahead, in August 2017, everyone in the continental U.S. will be no more than a 2-hour flight and quick car rental away from an umbral path that runs coast to coast from Oregon to the Carolinas.
But the total eclipse on Friday is drawing a special breed of "umbraphile." This one misses all the easy-to-reach destinations. Instead, the path of totality sweeps northeastward over the Arctic Ocean, making its only landfall on the remote Faroe Islands and the Svalbard archipelago — places some of you, I'll bet, have never heard of, let alone considered visiting.
The challenge is more than just getting to these remote islands, which are lovely (in a stark kind of way) but have limited resources to accommodate throngs of tourists. Here's the additional rub: at this time of year the prospects for clear skies are not particularly favorable anywhere along the track.
As Jay Anderson, a specialist in forecasting weather conditions for eclipses, explains, "The North Atlantic is a cloudy and stormy place, no more so than in March, being subject to three major cloud-making influences: a humid, ice-free ocean surface; a cold winter/spring atmosphere that saturates easily; and a location near the main track of low-pressure systems that leave the North American continent and venture across the North Atlantic and Barents and Greenland Seas."
So what's an eclipse-chaser to do? You start planning long in advance, that's what. Companies that specialize in eclipse-related travel have been advertising tours for at least a year, and many sold out quickly. Some of these are land-based, with lodging provided in Tórshavn, the capital and largest city in the Faroes, or in Spitsbergen, Svalbard's largest and only permanently populated island. Scores of private homes have been turned into temporary B&Bs.
Other travelers have booked passage on ships coming from Copenhagen, the British Isles, and elsewhere. At least these folks will have a modicum of mobility to "run" toward clear skies if the weather on Friday proves partly cloudy.Totality From On High
But for the ultimate in high-probability eclipse viewing, nothing beats being on an airplane. This approach only works if the eclipsed Sun is relatively close to the horizon (as it will be), and good views can only be had from one side of the plane. Quite a few airborne intercepts are planned — the skies over the Arctic Ocean will be a little more crowded than usual. Air Events, a German travel company, will dispatch three Boeing 737s. (I'll be on one of these!) Other private charters abound.
But the crowded airspace favors the well-prepared: eclipse flights that were to depart from Paris and Brussels have been cancelled. (Those passengers will be scrambling for seats — perhaps they'll be tempted to head to Murmansk, Russia, where an eclipse flight is said to be available for the rock-bottom price of 10,000 rubles, or about $165!)
Some enterprising eclipse-chasers have even found a commercial flight — Icelandair (FI) 450 — that will serendipitously pass through the lunar umbra while en route from Reykjavik to London. In fact, an airline representative says seeing totality will not be left to chance: "The flight plan for FI 450 Friday is dedicated to being in the right spot at the right time, and to turn the aircraft so that the passengers can enjoy the eclipse."Partial Views
Meanwhile, back on the ground, all of Europe (plus northern Africa and western Asia) will have to settle for a partial eclipse, which in some places will be quite dramatic. Cartographer Michael Zeiler has put a new spin on "how deep is deep": he's created a map that equates the strength of light from the partly covered solar disk to how much sunlight you'd experience on, say, Mars or Jupiter.
Finally, those of you stuck in the Americas are not completely out of luck, though you'll need to be an early riser. A handful of sites are intending to webcast views of the eclipse, starting around 4 a.m. Eastern Time:
"One Ring to rule them all." Join me as we explore a unique class of galaxies forged in the chaos of collision.
As Orion tilts to the west, the approach of spring offers a wonderful diversity of galaxies for telescopic viewing. Spirals. Ellipticals. Irregulars. Here and there among them are representatives of a rare breed — the ring galaxies. Shaped like onion rings, their formation is rooted in catastrophe.
Ring galaxies form when a small neighbor galaxy plunges through the disk of a larger spiral galaxy. The collision rarely results in any stars smacking into one another, but the gravitational shock acts like a tsunami that alters the orbits of stars and gas clouds, pushing them outward in excess of 150,000 mph (241,000 km/h). When the gas clouds collide, they compress and transform into a expanding ring of new star formation — think of an enormous wave crashing ashore in a frothy chaos of white foam.
Simulation of the collision between an elliptical and spiral galaxy to form the recently discovered "Auriga's Wheel" ring galaxy.
A typical ring galaxy still hangs on to its dense nucleus, but the once-majestic spiral arms have been recast as a striking stellar halo sparkling with young, massive blue stars. In Hubble Space Telescope images, ring galaxies appear temptingly bright. Unfortunately, most are faint and rather small, but not so much so that we can't track down at least a few with telescopes with 10-inches (25 cm) of aperture or more.
We'll check out three of them, Arp 143, Arp 141, and NGC 2793, all well-placed for viewing on March evenings. It's no surprise that two of them made it into astronomer Halton Arp's fascinating Atlas of Peculiar Galaxies, which includes numerous interacting pairs.
Our first stop will be Arp 143 in Lynx located high in the southern sky above Castor and Pollux at nightfall. Known also as NGC 2445 and NGC 2444, each is listed at magnitude 14, but they're clearly brighter than this. I would estimate 13. Through my 15-inch (37-cm) Obsession scope, both are immediately visible at low power as two separate objects.
The intruder, NGC 2444, is compact with a bright nucleus; its ring galaxy neighbor is one of the oddest galaxies I've ever set eyes upon. The nucleus appears is offset well to the north end of galactic center. Upping the magnification to 257x I could discern four glowing knots — HII star-formation regions — within the galaxy's amorphous, hazy outline. The knot south of the nucleus was easy enough, but the other three required averted vision and concentration to tease out.
At first glance the disturbed galaxy's clumpy appearance resembles a raisin pudding far more than a wheel. Where's the ring, you ask? Give it some time, say astronomers who've studied it closely. What we have here is a nascent ring on the cusp of a massive wave of star formation. We're witnessing the chaos of collision by neighboring NGC 2444, the distorted shape of which tells us it did not escape unscathed from its dashing pass.
Once you've cut your teeth on Arp 143, you're ready for UGC 3730, or Arp 141, a 13th-magnitude ring galaxy in Camelopardalis located about 10° northwest of Ursa Major's bright M81-M82 galaxies. Arp 141's core is a strange beast with an obscured nucleus and tortured ring. Like Arp 141, it's faintly but immediately apparent as a fuzzy patch about 2.5′ long and extended north-south at 64x. Closer inspection at 257x shows the elliptical member as a "fuzzy star".
With averted vision I could clearly see the fainter ring galaxy and a bright patch (HII region?) where they touch. The ring shape itself was visible only fleetingly. I bet an 18-incher would reveal it.
Our last stop is NGC 2793, conveniently located less than 1° west of 3rd-magnitude Alpha Lyncis. This little button of a galaxy measures just 1′ across and glows at a modest magnitude 13. As with the others, it's easy to spot but takes concentration to ferret out the details that reveal its nature. Many ring galaxies aren't that difficult to find, but seeing the contrast between the ring and the rest of the galaxy can be challenging.
With high magnification I can see a brighter, non-stellar nucleus off to the galaxy's east side; honing in by alternating averted with direct vision, I glimpsed several tiny "sparkles" or knots of what are doubtless new star clusters within its southeastern border. Overall, the galaxy's eastern third appeared brighter and denser than the hollowed-out portion seen in the photo above.
This trio of rings is seasonal and samples only a small number of an already small class of galaxies. I encourage you to explore them as well as others. A simple click will download a .pdf with photos of 40 others in this illustrated ring galaxy catalog, enough to guarantee many nights of delicious exploration. You may also find this Color Atlas of Ring Galaxies helpful.
Get to know the night sky with select Sky & Telescope products!
The post High Point Monument, Snow Squall & the St.Patrick’s Day Aurora of 03/17/15 appeared first on Sky & Telescope.
With just weeks left before it crashes into its host planet, NASA's Messenger spacecraft is making the most of its extremely low altitude and finding that Mercury isn't a completely dead world.
There's been so much planetary exploration going on — from Chang'e 3 on the Moon to Dawn reaching Ceres to New Horizons readying for its historic Pluto flyby — that we tend to overlook some of the spacecraft still doing their thing around other worlds. One of those is Messenger, which tomorrow celebrates its fourth anniversary of entering orbit around Mercury. (That event wasn't beginning of the planet's reconnaissance, however, as the spacecraft had already zipped by at close range three times in 2008 and 2009.)
Messenger's work is nearly finished. Fuel reserves are extremely low, and in a matter of weeks ground controllers will no longer be able to keep the craft's highly elliptical orbit stabilized. In fact, due to gravitational perturbations from the Sun, Messenger keeps edging closer and closer to the Mercurian surface. Only occasional boosts from the craft's thrusters are preventing an outright collision.
"We only have about 6 weeks to go in the mission," project scientist Sean Solomon noted during a press briefing yesterday. Five more thruster firings are planned. "We'll exhaust every last kilogram of propellant," Solomon vows, even expelling the helium used to pressurize the fuel in an effort to keep Messenger going. With luck, the end won't come until around April 30th. Then the golf-cart-size, half-ton craft will slam somewhere into the planet's mid-northern hemisphere.
But for now, the spacecraft continues to return abundant results. In fact, Messenger's "low-altitude campaign," which has been ongoing since last April, allows the craft's eight experiment teams to make observations far more detailed than those acquired earlier in the mission. These close passes benefit its camera, of course, but it's also a boon to the elemental assays made using the X-ray, gamma-ray, and neutron spectrometers on board. These devices can't be pointed — they "see" a very wide swath of the surface as a single pixel. So the closer Messenger comes to the surface, the smaller the patch of Mercurian they sample.Complex Geochemistry
Visibly, there's not much variation on the planet's surface. Colorations are subtle, suggesting that the planet lacks any distinct changes in regional geochemistry. But a different picture has emerged thanks to the high-energy spectrometers. For example, the distribution of magnesium (common in rock-forming minerals) varies wildly from place to place. In some locales it's as common as silicon, but in "fresh" exposures near young craters the magnesium signal nearly disappears.
One of the fundamental questions about Mercury is how it attained its unique overall composition — a disproportionately huge iron-rich core surrounded by a relatively thin silicate exterior. Messenger scientists had hoped that getting a handle on the surface composition would provide strong evidence for one of a few different ideas about how Mercury became the "Iron Planet." But at a briefing yesterday discussing recent Messenger results, geochemist Larry Nittler admitted, "I would argue that we still don't know the answer to that question a whole lot better than we did before we went into orbit."
The problem isn't a lack of data but rather a lack of detailed modeling, he explains. One oft-discussed idea is that a giant impactor smashed into young Mercury and stripped away most of its crust and mantle, leaving behind that giant cannonball of a core and not much else. Such a blast should also have bled off virtually all of the "volatile" elements (those with low melting points), such as sulfur, sodium, and potassium. Yet the Mercurian surface exhibits an abundance of volatile elements — and yet very little iron — leaving geochemists like Nittler scratching their heads.Strange Surface Features
Imaging scientists are also getting an eyeful from the lower orbit, and the spacecraft's camera has been recording some key targets with resolutions of just a few meters per pixel.
Closer scrutiny is paying big dividends concerning the puzzling "hollows" seen early in the mission. Usually brighter than their surrounding and often confined to the floors of impact craters, these tight clusters of small pits are now being seen extremely well — in some cases with 50 times better resolution than early views had. The hollows inside Scarlatti basin, for example, are all a few tens of meters deep. "They grow and ultimately stop growing," observes David Blewett, a researcher at Johns Hopkins University's Applied Physics Laboratory.
The emerging consensus is that some compound in the near-surface rocks, perhaps a type of sulfide, is vaporizing away once it gets exposed to the intense sunlight, radiation, and incessant bombardment from micrometeorites at the surface. As it escapes to space, holes are left behind. Moreover, the new close-ups show that, unlike the terrain surrounding them, the hollows exhibit very few impact craters. So they've not been there very long, geologically speaking. Blewett thinks they must be "younger than a few tens of millions of years and might well still be actively forming today."
Meanwhile, Thomas Watters, a researcher at the Smithsonian Institution's National Air & Space Museum, has been keeping track of little fractures in the planet's crust. Mercury is scarred by some truly big cracks, some hundreds of kilometers long. These thrust faults formed eons ago as the planet cooled and gradually shrank in volume. The circumference shrank too, causing the already-solid crust to crack and crumple. (Imagine what happens to the skin of a apple as it gradually dries out.)
Recently Watters and others have noticed plenty of smaller compression fractures across the surface, many less than 10 km long and only tens of meters high. As with the hollows, these mini-fractures appear to have formed quite recently — "so young," Watters notes, "that they're probably forming today."
Yesterday's briefing also addressed the deposits of water ice that lie at the permanently shadowed bottoms of craters near the planet's north pole. In some cases, the ice might actually be exposed, but elsewhere researchers believe it's covered with a dark, organic-laced protective veneer. Messenger's extended mission has allowed scientists to take intentionally overexposed images of these always-dark crater floors, with surprising results. The dark veneers typically have a sharp boundary, observes Nancy Chabot (JHU-APL) — too sharp to have been around for along time. "This must either be young or an ongoing process," she explains.Next Up: BepiColombo
Even after Messenger's impending demise, the mission team has plenty of stockpiled observations to work though and the the scientific hits should keep on coming for a while. Geochemists are also looking forward to getting results from the European Space Agency's BepiColombo, a follow-on orbiter scheduled to launch in 2017 and arrive at Mercury in 2024. Its 11-instrument payload includes one key experiment that Messenger lacks: a spectrometer attuned to thermal-infrared wavelengths. Its results should reveal the surface's true composition — and, with that, likely the key to understanding what happened to Mercury all those eons ago.
Thanks to Messenger's extensive reconnaissance, you can now explore this mysterious planet yourself with Sky & Telescope's exclusive Mercury globe.
The 1979 Isolated Triplets of Galaxies catalogue contains 84 northern hemisphere trios identified by Valentina Karachentseva and Igor Karachentseva through a visual inspection of the Palomar Observatory Sky Survey plates. The astronomers labeled triplets of galaxies "isolated" if the nearest significant neighbor was at least three times as far away as the separation of the group's components. In the May 2015 issue of Sky & Telescope, contributor Steve Gottlieb discussed his observations of three isolated triplets (KTG 54, 55, and 57). Here, he has made available data distilled from the Karanchentseva catalog and his own observations so you can go even deeper with this unique set of targets (download as an Excel file).
Steve has given both the KTG numbers and more common catalogue names (for instance, KTG 01A is better known as M110). The RA and Dec are 2000.0 coordinates. Magnitudes are V (visual) unless indicated otherwise (the Karanchentseva catalogue gave blue photographic magnitudes). The radial velocity and galaxy type data come from the original catalogue.
Copyright © 1999-2010 Falak Online. All rights reserved. Powered by Drupal.
Penafian: Falak Online tidak bertanggungjawab terhadap sebarang kehilangan atau kerosakan yang dialami kerana maklumat dalam laman web ini.