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
North Americans have front-row seats when the Moon covers up the brightest star in Taurus.
On the evening of January 19th, observers all across North America can witness the Moon covering, and then uncovering, the 1st-magnitude star Aldebaran (Alpha Tauri). It happens in the evening. High in the sky. On the Moon's dark limb rather than the bright limb. For almost all of the U.S. and Canada. What's not to like?
This is another in a series of 49 monthly Aldebaran crossings that will continue through September 2018. But most of them don't happen for wherever you are, and nearly half of those that do occur in daylight (though don't let that stop you; Aldebaran is bright enough to glimmer through a clear blue sky in a telescope, as occurred last October 2nd).
The Moon on the evening of the 19th will be waxing gibbous. A waxing Moon leads with its dark edge as it moves along its orbit against the starry background. So Aldebaran will disappear on a dark background away from the dazzling glare of the sunlit lunar surface.
With the Moon 82% illuminated, its night portion will probably be too weakly Earthlit to show in a scope. So you'll have to keep a steady watch as Aldebaran's time draws near to catch it the moment it vanishes. Its reappearance on the bright limb will be less obvious, but still easy to see if you're watching.
You can estimate when the star will disappear and reappear for your location using Sky &Telescope's Aldebaran occultation charts, shown at right (click on each for a larger view).
Or you can refer to these detailed timetables for many locations. (Note that this link provides three separate tables: for the disappearance, the reappearance, and the locations of cities).
The occultation's southern limit — the graze line where the star skims the Moon's southern limb — runs from south Georgia near the Gulf Coast and across South Texas. Along this line you might see the star wink out and back more than once as it skims behind lunar hills and valleys along the southern limb.
Aldebaran has a large apparent disk as stars go, 21 milliarcseconds wide. That's as big as a pea seen from just 15 miles (25 km) away. So you might see Aldebaran fading and reappearing not quite instantaneously if the Moon's edge skims it at a low angle from your location. A grazing occultation is the only way an amateur can "resolve" the face of a star other than the Sun. A nearby orange or red giant like Aldebaran offers your best chance.
Over the next two weeks, for the first time in more than a decade, you can see all of the naked-eye planets — from Mercury to Saturn — together in the predawn sky.
If you follow celestial comings and goings at all, you know that bright planets have been largely missing from the evening sky for a few months. Sure, with careful watching you could have spotted Saturn low in the southwest as late as November, and Mercury put in a brief appearance a few weeks ago.
But really all the action has been in the sky before sunrise. Anchored by bright Venus and Jupiter, joined by Mars and Saturn, this planetary fab four has been dominating skywatchers' attention for months. (Did you catch last October's triple play involving Venus, Jupiter, and Mars?)
The show far from over. In fact, during the next two weeks you'll have a good chance to view five planets at once. It's a real visual treat, so don't pass up the chance to see it.
(You might see posts elsewhere that suggest this event runs from January 20th to February 20th. Technically, that's true — in his book More Mathematical Morsels, celestial dynamicist Jean Meeus notes these dates. But realistically you're not going to see Mercury linger in the predawn sky for a whole month. Instead, I suggest that the last week of January and first week of February are your "best bets" for success.)
Let's set the stage. You'll need to be outside about 45 minutes before sunrise. This time of year, if you work or go to school, you're usually already up by then — maybe even well positioned to scan the predawn eastern horizon as you commute to work or head off to school.
Venus is obvious as it lingers above the southeastern horizon. It's actually in decline, not nearly as high up as you saw it toward the end of 2015. But Venus has no equal for brightness among the night's planets and stars. Way over to the right, on the southwestern side of the sky, is Jupiter. In between are four bright beacons: not far from Venus are Saturn and, below it, the star Antares. Shift your gaze farther right to sweep up Mars, then the star Spica, and finally Jupiter.
The fifth planet is Mercury, which was spotable low in the southwest after sunset just two weeks ago. But it's been racing rapidly from evening to morning visibility. (The fleetest of planets can do that, since it circles the Sun in just 88 days.)
Your first good chance to spot Mercury before dawn comes later this week. By Friday, the 22nd, find a clear view toward southeast and look 5° above the horizon. That's about the width of your three middle fingers held together at arm's length. It's along a diagonal from Saturn through Venus, about as far from Venus as Saturn is. Day by day, Mercury will appear a little higher up and a little brighter. By month's end, it'll be easy to spot.A Plane of Planets
As you sweep your gaze from Mercury toward Jupiter, an arc of roughly 110°, notice that all these planets line along a single arc across the sky. That's no accident. All of the major planets lie very near the plane of Earth's orbit, which projects as a line — the ecliptic — across the sky. By defniition, the Sun always lies on the ecliptic — and our Moon is never far from it either. It's the superhighway of planetary motion among the stars.
As you're gazing at all these planets, think about their varied distances from us? Astronomers use the average Earth-Sun distance, called an astronomical unit, as a handy yardstick for intra-solar-system distances. Of the five planets you're seeing, right now Mercury is closest (about 0.8 a.u.), followed by Venus (1.3), Mars (1.4), Jupiter (4.7) and Saturn (10.6). The reflected sunlight you see coming from mercury took a brief 6½ minutes to reach Earth, where that from Saturn took just under 1½ hours to get here.
But don't let the vastness of interplanetary space keep you from enjoying for the simple visual beauty that awaits you before dawn. We haven't had this opportunity since this time 11 years ago. Back then their order in the sky briefly matched their relative order outward from the Sun. This time, Mars and Saturn apparently didn't get the memo, but we'll happily overlook that, right?
A new technique lets astronomers measure nearly invisible clouds of hydrogen gas from across the universe.
Most of the universe is hidden from view. The world’s best telescopes can’t pick up rocky asteroids that orbit the far reaches of the solar system, exoplanets that circle distant stars, or galaxies that formed in the early universe. Instead, science is often done in silhouette. Astronomers spot such evasive objects only by the shadow they cast when they pass, by chance, in front of a more distant light source.
A new study improves upon that method, bringing to light so-called damped lyman-alpha systems, giant clouds made mostly of hydrogen gas in the early universe. Jeff Cooke (Swinburne Institute of Technology, Australia) and John O’Meara (Saint Michael’s College) announced at the American Astronomical Society meeting in Kissimmee, Florida, that they’ve found one of these clouds that spans three times the width of the Milky Way.
Because neutral hydrogen emits no radiation, damped lyman-alpha systems are notoriously difficult to detect directly. Instead, astronomers use a simple trick: they catch the clouds’ shadows. The flood of light from distant quasars — a class of intensely bright galactic cores with supermassive black holes that are gobbling down gas and dust — casts a spotlight on otherwise invisible gas. Any intervening hydrogen atoms absorb a specific wavelength of the quasar’s light, leaving a dark absorption line in the spectrum that reaches Earth.
The shape and depth of that absorption line reveals some information about the intervening cloud. Astronomers now know, for example, that a similar total amount of hydrogen gas exists in these early clouds as in the interstellar medium of most galaxies today. As such, they’re a good proxy for the star-forming regions within galaxies in the early universe. Detailed measurements of these clouds could therefore shed light on how galaxies form and evolve.How Big Are They?
To date, astronomers have used absorption lines within quasars’ light to study thousands of damped lyman-alpha systems. But there’s one big disadvantage. Because quasars themselves are very small objects, only a few light-years across, astronomers can only probe a tiny portion of these systems. Cooke compared this problem to illuminating a massive college campus with just the tip of a laser pointer. You’ll likely only spot a blade of grass or a sliver of a cement rooftop.
“For 40 years we've been using this technique to understand gas in early galaxies, but we've been missing out on two really important, fundamental pieces of information,” says O’Meara: the clouds’ sizes and masses. “That's kind of embarrassing.” As such, astronomers are unaware if these systems are just small clouds within a galaxy or massive clouds within the intergalactic medium that are ready to form a galaxy.
So Cooke (pronounced like the treat) and O’Meara decided to look for background galaxies instead. A larger background light source will illuminate far more — if not all — of an intervening cloud and reveal unprecedented detail. Distant galaxies are usually too faint to use as spotlights, but the technique becomes feasible with larger telescopes coming online in the near future.Shadow of an Ancient Galaxy
As a proof of concept Cooke and O’Meara looked for damped lyman-alpha systems in the signatures of 54 bright galaxies using the Keck Observatory’s twin 10-meter telescopes and the Very Large Telescope’s four 8.2-meter dishes. One galaxy, known as VVDS 910298177 (located at a time when the universe was only 3 billion years old), clearly showed a damped lyman-alpha system. The absorption line drops all the way to zero all the way across the background galaxy, which means that the gigantic cloud in front of it must cover the whole thing. That makes the cloud at least three times the size of the Milky Way — much larger than astronomers could have guessed given a background quasar.
“So what we've done is increased our ability of understanding the size of things by about a factor of a hundred million, which is really kind of cool,” says O’Meara.
The finding might help solve the puzzle of where these early clouds reside. "The damped lyman-alpha systems we've found appear to be essentially 'stand alone' clouds in the intergalactic medium," says Cooke. They are so large that they "will likely form full mature galaxies like the present-day spiral galaxies like the Milky Way."
Dawn Erb (University of Wisconsin Milwaukee), who was not involved in the study, thinks the method will be a useful complement to the work she does. Erb studies galaxies at similar cosmological distances, but she does so by looking at their emitted light, rather than their absorbed light. By looking at these galaxies in both emission and absorption, she says, astronomers can gain a far better understanding of their overall morphologies.
The new technique holds a lot of promise in the era of 30-meter telescopes. “These monster-machines that are getting built are going to be able to use this technique by the thousands,” says O’Meara. And they’ll do so much more in 18 hours than Cooke and O’Meara were able to accomplish on the Very Large Telescope. There are far more galaxies than quasars in the first place, so soon enough astronomers will be able to “map out a three-dimensional tomography of all of the gas in the universe,” says Cooke.
Jeff Cooke and John O’Meara “A New Constraint on the Physical Nature of Damped Lyman Alpha Systems.” Astrophysical Journal Letters, 2015 October 15.
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Teeter's Telescopes unveils its latest custom Dobsonian telescope, the 16-inch f/4.5 TT/Stark (starting at $2,575 without optics). This Truss-Dobsonian is an "á la carte" telescope that you can customize yourself at time of order or later. Each unit is manufactured from Baltic birch plywood with Teeter's exlusiev clear-gloss finish. Its mirror box weighs approximately 55 pounds (25 kg, including its optional primary mirror) and stands 69 inches when pointed at the zenith. Each TT/Stark Dobsonian can be ordered with a variety of options, from the primary optics to the focuser and finder, and is compatible with most popular upgrades and accessories.
SkyandTelescope.com's New Product Showcase is a reader service featuring innovative equipment and software of interest to amateur astronomers. The descriptions are based largely on information supplied by the manufacturers or distributors. Sky & Telescope assumes no responsibility for the accuracy of vendors statements. For further information contact the manufacturer or distributor. Announcements should be sent to nps@SkyandTelescope.com. Not all announcements will be listed.
The most luminous supernova ever discovered, ASASSN-15lh, challenges a popular theory for blazingly bright exploding stars.
About six months ago, we alerted readers to the discovery of the most luminous supernova ever. Now the discovery team is releasing additional information, and it strains even the most extreme physical scenarios.
The explosion of light initially appeared in June 2015 as the faintest of dots in automated images taken by the All-Sky Automated Survey for Supernovae (ASAS-SN), which repeatedly observes the same areas of sky to look for ephemeral bursts of light. Sophisticated software spotted the sudden but subtle influx of light, prompting astronomers to go fishing for follow-up observations at several telescopes. They soon found that the light from the source, dubbed ASASSN-15lh, had traveled for 2.8 billion years to reach Earth.
Due to its distance, ASASSN-15lh only reached about 17th magnitude at its brightest, but its luminosity outshone any supernova yet discovered. Even months later, this single object continues to emit more energy per second than all the stars in the Milky Way.
Subo Dong (Peking University, China) and colleagues released an update to the discovery data in January 15th’s Science. Following a spate of follow-up spectra, the team continued to track the supernova’s goings-on using the Las Cumbres Observatory Global Telescope Network (LCOGT; see the October 2012 issue of Sky & Telescope for more on this ambitious project) and the Swift space telescope. The light curves they obtained showed how the supernova’s brightness changed over time.
They also documented an outpouring of energy that challenges the extreme scenarios that attempt to explain this rare event.Assassinating Expectations
ASASSN-15lh exhibits characteristics typical of exploding stars (such as blue-colored light that brightens suddenly before fading more gradually away). It lacks hydrogen and helium lines in its spectrum, so it looks similar to Type Ia supernovae, which come from exploding white dwarfs.
But its brightness puts it in the class of so-called superluminous supernovae. These rare diamonds in the rough shine about 10 times brighter than their more common Type Ia cousins, and ASASSN-15lh is the brightest of its class.
Even among its peers it’s a bit odd, because the explosion appears to be much hotter than normal. Its home is unusual, too, a bright but otherwise unassuming galaxy that forms less than a star per year. Previous superluminous supernovae have been found in furiously star-forming dwarf galaxies. Massive stars, which live fast and die young, are expected in star-forming regions, but not necessarily in the stagnant environment where ASASSN-15lh appears to reside.
Astronomers have a hard time explaining why superluminous supernovae exist. One scenario, used to explain other objects in ASASSN-15lh’s class, says that the outer layers of a massive exploding star collide violently with material around the star, making the explosion appear brighter in the process. But ASASSN-15lh’s spectrum doesn’t display any hydrogen lines, which would be common in the circumstellar material, so this explanation is ruled out straightaway.
Another scenario, and perhaps the most promising to date, suggests a more exotic power source. When a massive (but not too massive) star goes supernova, its core implodes to form a spinning neutron star. And if the circumstances are right, these crushed stellar remains could carry extreme magnetic fields, potentially 100 trillion times the average magnetic field on the Sun. These super-magnetic, rapidly spinning neutron stars, called magnetars, could power something far brighter than an ordinary exploding star.
Magnetars could explain other superluminous supernovae, but this time there’s a catch. Already, ASASSN-15lh has emitted more energy than a magnetar could provide: 1052 ergs, or 100 billion times more than what the Sun emits over the same time period. And that’s only the energy emitted over the supernova’s first four months, which is what’s published in the Science paper. “Now we have collected a few months more data,” Dong adds, “and the integrated luminosity has exceeded 1052 by considerably more.”
“To me, magnetars have played in recent times the role of jokers in card games,” says Tsvi Piran (Racah Institute of Physics, Israel). “Whenever one needs an additional energy source, a joker is invoked. If you look at the wide range of ways that magnetars have been invoked to operate, you can see clearly that not all of them can work at the same time.”
Our Constellation Basics webinar gives vital background information about the major winter constellations. But just as you can't learn to ride a bicycle by reading a book, you can't learn the constellations from the comfort of your own living room. You need to go outside and look -- with the aid of an interactive resource.
The oldest tool for learning the constellations, and still one of the most effective, is a planisphere, also called a star wheel. It includes a chart of all the constellations ever visible from your location plus a sliding window that shows you which ones are visible at any given date and time. Senior editor Alan MacRober explains how to use a planisphere in this video. Sky & Telescope sells a full selection of planispheres, including a unique model that omits the faintest stars, showing only the constellations that are obvious from a typical suburb.
Versatile as they are, planispheres have two drawbacks. Because they include all the stars visible at every season, the ones that happen to be visible at any moment end up in a fairly small window, and they're also somewhat distorted. And they cannot show the positions of the planets, which are constantly changing.
For those reasons, it's often convenient to have all-sky charts tailored for the specific month when you're using them. Every issue of Sky & Telescope includes a 2-page all-sky chart, together with a calendar showing special events for the month in question. SkyWatch, our annual magazine, includes single-page charts for each month bundled together in one convenient package. Or you can download a printable 2-page chart for the current month at Skymaps.com.
Electronic devices are more versatile still, because they can be customized not only according to the date and time but also for specific locations. And you can zoom in or out. Sky & Telescope's Interactive Sky Chart is extremely popular for use on computers. To achieve more flexibility (at the cost of more effort), you can download and install a planetarium program, including the popular freeware Stellarium.
Smart phones and tablets are much more convenient than computers for outdoor use. Sky & Telescope's free SkyWeek app lists interesting celestial events for every day of the current week, and if you press the View button, it brings up a sky chart showing that event. You can then pan, zoom, and change the time to find all of the constellations and planets that are visible that night. The underlying engine is a stripped-down version of the hugely popular SkySafari app. Even the cheapest version of this app shows the sky in great detail. You can also point your device anywhere in the sky, and Sky Safari will show a labeled chart of whatever you're looking at -- a tremendously useful feature.
For additional background information, see our complete list of constellation names and abbreviations, which includes an audio guide to pronunciation. Probably the best succint online resource for constellation history is Ian Ridpath's wonderful book Star Tales, which is also available in print.
The post Constellations with Tony Flanders: Accompanying Resources appeared first on Sky & Telescope.
Black holes may have a limit to how much they can eat in the public eye.
Even the most gluttonous black hole reaches a point when it pushes itself away from the public buffet line, preferring instead to sneak its treats on the sly..
The gluttony limit of a black hole is around 50 billion times the mass of the Sun, according to calculations by Andrew King (University of Leicester, UK, and University of Amsterdam, The Netherlands). By some deceptively simple reasoning published in the December 10, 2015, Monthly Notices of the Royal Astronomical Society, King shows that once a black hole reaches this mass, the disk of gas that acted as the black hole’s dinner buffet begins to crumble apart, collapsing under its own weight into stars.
The gaseous disk that feeds growing black holes is what enables us to see these dark objects, even from a distant universe less than 1 billion years old. Take away the gas and you take away the visible and ultraviolet light that signals a black hole’s gorging.
“If the black hole is very massive, then the gas disc would have to be correspondingly large and massive,” explains Zoltan Haiman (Columbia University). “The main idea in King’s paper is that above a certain mass, the gas in such a disk would be gravitationally unstable — i.e., it would collapse into clumps under its own weight, before the gas can funnel inward into the black hole.”
In other words, even the immense gravitational pull of a 50 billion solar-mass black hole can’t overcome the self-gravity that clumps up the surrounding matter.
“I find this idea very compelling,” Haiman says.
But that’s not to say the black hole stops growing altogether. It just has to gobble down mass in secret, without emitting any light. A star might happen to fall straight into it, swallowed whole, or it could merge with another black hole.
Astronomers have found black holes with masses of around 10 billion Suns, near King’s theoretical limit, but they’ve found them by looking for the accretion disk’s beacon of light. “The mass limit means that this procedure should not turn up any masses much bigger than those we know, because there would not be a luminous disk,” King said in a press release.
Yet it’s possible that even bigger behemoths might sit silently in nearby galactic centers. To find them, astronomers will have to turn to more indirect means of detection, such as gravitational lensing.
Friday, January 15
• After dinnertime in January, the Great Square of Pegasus balances on one corner high in the west. Tonight the Moon (nearly first-quarter) marks the way by shining to the left of it, as shown here.
The whole Pegasus-Andromeda constellation complex runs all the way from near the zenith (Andromeda's foot) down through the Great Square (Pegasus's body) to somewhat low in the west (Pegasus's nose).
Saturday, January 16
• First-quarter Moon (exact at 6:26 p.m. EST). The Moon shines in dim Pisces upper left of the Great Square of Pegasus, as shown above. Does the half-lit Moon look just a trace bigger than usual? It's about at perigee.
Sunday, January 17
• If you don't know Kemble's Cascade, it's a lovely binocular asterism in Camelopardalis north of Perseus now high overhead. It's a straight stream of mostly faint stars 2° long, running northwest to southeast. You can use the finder chart in Gary Seronik's Binocular Highlight on page 43 of the January Sky & Telescope. Most of its stars are too faint (7th or 8th magnitude) to show on that chart, but the black circle there is centered on its 5th-magnitude middle star.
Monday, January 18
• Jupiter's outer big moon, Callisto, disappears into eclipse by Jupiter's shadow — slowly, gradually — around 12:32 a.m. Tuesday morning EST; 10:32 p.m. Monday evening MST.
• Bright Capella high overhead, and equally bright Rigel in Orion's foot, are at almost the same right ascension. This means they cross your sky’s north-south meridian at almost the same time (around 9 or 10 p.m. now, depending on how far east or west you live in your time zone). So whenever Capella passes its very highest, Rigel marks true south over your landscape.
Tuesday, January 19
• The dark limb of the waxing gibbous Moon occults Aldebaran this evening for most of North America. See the time-prediction maps in the January Sky & Telescope, page 49. You can also get local timetables for the star's disappearance and reappearance. The Moon will be 82% sunlit.
Wednesday, January 20
• Sirius twinkles brightly after dinnertime below Orion in the southeast, far below the Moon. Sometime around 8 or 9 p.m., depending on your location, Sirius shines precisely below fiery Betelgeuse in Orion's shoulder. How accurately can you time this event for your location, perhaps using a plumb bob or the vertical edge of a building? Sirius leads early in the evening, Betelgeuse leads later.
Thursday, January 21
• Tonight the 9.9-magnitude asteroid 115 Thyra will briefly occult a 9.0-magnitude star near the Beehive cluster in Cancer for telescope users along a narrow track from southern New Jersey through the San Diego area. Watch them merge before their combined light suddenly drops by 1.3 magnitudes for up to 7 seconds. Track map, finder charts, time predictions.
Friday, January 22
• The nearly-full Moon shines in Gemini this evening, with Castor and Pollux to its upper left and brighter Procyon to its lower right, as shown here.
• On the other side of the sky, the big Northern Cross of Cygnus plants itself upright on the northwest horizon soon after the end of twilight.
Saturday, January 23
• Full Moon (exact at 8:46 p.m. EST). As the Moon climbs the eastern sky this evening, look for Pollux and Castor above it and Procyon to its right. It's currently 4° south of the ecliptic; in a telescope, look for features on its northern limb casting extremely thin shadows even at the time of full Moon.
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.
Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or new Jumbo Edition), which shows stars to magnitude 7.6.
Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5, nearly three times as many. Next up, once you know your way around, is 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, or the bigger Night Sky Observer's Guide by Kepple and Sanner.
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
Mercury is buried in the glow of sunrise.
Saturn (magnitude +0.5) and brilliant Venus (–3.9) are low in the southeast in early dawn. Venus is getting lower, while Saturn is moving higher to Venus's upper right. They're 8° apart on January 16th and 16° apart by the 23rd. Throughout the week, Antares (magnitude +1.1) shines 7° lower right of Saturn.
Mars (magnitude +1.1, in eastern Virgo), glows high in the south in early dawn. This week it moves from 13° to 17° left of Spica, its twin for brightness but not for color!
Jupiter (magnitude –2.3, between Leo and Virgo) rises in the east around 9 or 10 p.m., shines highest in the south around 3 or 4 a.m., and moves over to dominate the southwestern sky by early dawn. It's on its way to opposition March 8th.
Uranus (magnitude +5.8, in Pisces) is still well up in the southwest just after dark. Finder chart.
Neptune (magnitude +7.9, in Aquarius) is getting very low in the west-southwest after dark.
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 Standard Time (EST) is Universal Time (UT, UTC, or GMT) minus 5 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
On Thursday evening January 21st, I'll be hosting Tony Flanders — longtime S&T writer and editor, host of the beloved SkyWeek TV show, and devoted naked-eye skygazer — for a live webinar that will tour the signature winter constellations and discuss what constellations are all about. And, we'll be taking questions.
Did you know that our capital letter A may have originated from the face of Taurus the Bull? Or that Orion was once a woman? Come join us for this live webinar on the night of January 21st at 9:00 p.m. Eastern Standard Time (6:00 p.m. Pacific Time and 2:00 on January 22nd UT/GMT).
And if you can't make it to the live event or want to download it for future classroom or outreach use, don't worry — we'll make a recording of the webinar available in our online store soon afterward!
The physics and astronomy world is all agossip: has LIGO heard its first black-hole merger? Well, not so fast.
Rumors are swarming on social media that the newly upgraded LIGO, the Advanced Laser Interferometer Gravitational-Wave Observatory or aLIGO, has finally seen the gravitational-wave signature of two stellar-mass black holes spiraling together and merging. Maybe even two such events since September. Or not.
Such an observation would confirm one of the most elusive predictions of Einstein’s general theory of relativity, and it would also open a new field of cosmic observation: gravitational-wave astronomy.
First, the background: According to general relativity, any accelerating mass should produce weak ripples in the fabric of spacetime itself. But it would take enormous, dense masses accelerating extremely fast to emit a significant amount of them. Neutron stars or black holes spiraling together and merging would qualify, and LIGO was built with those events particularly in mind.
As gravitational waves pass by, they stress and compress time and distance. But after traveling millions of light-years across the universe, they would be extremely weak. The typical expected signal strength would stretch and squeeze the distance from the Earth to the Sun, for instance, by the width of a hydrogen atom. Yet even that weak an effect could be detected by the laser beams bouncing back and forth along LIGO’s 4-kilometer-long vacuum pipes. It would be the first direct detection of gravitational radiation. (We already know it exists by its indirect effect of draining orbital energy away from close neutron-star binaries.) A Nobel Prize probably awaits the first direct observation. If it ever happens.
Such a feat “will open up a new window into the way we see the universe,” says astronomer Takamitsu Tanaka (Stony Brook University). Take gamma-ray bursts, for instance. These are quick, incredibly powerful explosions that are presumed to come, in some cases, from a pair of neutron stars spiraling together and merging, and in other cases from the fraction-of-a-second disruption of a dying star’s neutron-star-like core. Both kinds of cataclysm should be violent enough to send detectable gravitational waves far across the universe. “If we could see such events from gravitational-wave and conventional telescopes [both], then we can learn a lot more about the physics and what’s really going on with those events,” says Tanaka.
Still, the rumors remain just rumors. And they’re really bothering the LIGO people.Gravitational Whispers
The gossip started spreading in physics circles just a week after the upgraded aLIGO began running in September. The rumors escaped from physics circles when cosmologist Lawrence Krauss (Arizona State University) tweeted about them on September 25th: “Rumor of a gravitational wave detection at LIGO detector. Amazing if true. Will post details if it survives.” More recently he commented that he’s 60% sure the story will pan out. Yesterday he noted the caveat that he is not one of the 900-plus members of the LIGO scientific collaboration, nor does he represent anyone there.
Steinn Sigurdsson (Pennsylvania State University), who has also speculated on the rumors via social media, says “I have absolutely no inside information on what is going on. I hear stories, I can make inferences, I can see patterns in activity. And there has been a consistent whisper for several months now that [aLIGO] saw something as soon as they turned it on.”
Those whispers grew to a lively babble after further tantalizing clues. First, Sigurdsson points to a flurry of papers that have appeared this week on the arXiv preprint server that were curiously specific. Astronomers, says Sigurdsson, “posted somewhat different scenarios for ways in which you could have black hole binaries form, all of which coincidentally predicted almost the exact same final configuration, and said ‘Gosh our model predicted that this very specific sort of thing will be the most likely thing that LIGO sees.’ ” And Sigurdsson isn’t the only one who has noticed. Derek Fox (Pennsylvania State University) pointed to one paper, for example, tweeting “this seems a rather specific GW [gravitational wave] scenario to pull out of thin air?”
But again, Krauss, Sigurdsson, and Tanaka claim to have no privileged information. “It’s the equivalent of watching for pizza deliveries at the Pentagon,” says Sigurdsson. He’s referring to the open-source intelligence technique that Washington reporters reportedly used to spot when big events were about to emerge based on the number of late-night pizzas delivered to the White House. “You can play the same game with physicists,” he says. (Unfortunately there have been no reports of LIGO ordering an overabundance of Domino's.)
Second, it’s a small community. So when a few collaborators — who all happen to be members of LIGO — duck out of a future conference due to new overlapping commitments, it doesn’t go unnoticed. A similar pattern played out right before physicists announced the discovery of the Higgs boson. Based on dates cancelled, Sigurdsson speculates that an announcement will come from the team on February 11th.
Details of the supposed detection, however, were not publicly bandied about until Monday, when theoretical physicist Luboš Motl posted on his blog the latest version of the rumor: that aLIGO has picked up waves produced by two colliding black holes each with 10 or more solar masses. He also said he’s been told that two events have been detected.Reason for Silence
There’s a good reason why LIGO’s people refuse to confirm or deny that something is going on. Scientists really want to get things right before they announce a major finding to the world, whether positive or negative. LIGO’s data-analysis task alone is vast and full of potential gotchas, and the most likely gravitational-wave detections would be buried deep in the noise. The experiment is looking for changes in the distance between mirrored blocks of metal 4 km apart as slight as 10–22 meter, about a millionth the diameter of a proton. In other words, changes in measurement of 1 part in 1025. What could possibly go wrong?
Fresh on the minds of everyone in astronomy and physics is an announcement fiasco that blew up spectacularly in 2014. The astronomers of the Harvard-based BICEP2 collaboration announced to the world’s media, at a packed press conference, that they had very likely discovered primordial gravitational waves from the earliest instant of the Big Bang. The signal was unexpectedly strong. It would have been the much-sought, crowning evidence for the inflationary-universe theory of how the Big Bang happened. Not until later did their work go through full peer review. The discovery literally turned to dust — leaving a very public mess and a lot of criticism. Many dread a repeat.
The current excitement could easily be a false alarm. Even if LIGO has a promising signal, it may be a false test signal planted as a drill. It's been done before, in 2010 near the end of LIGO's last pre-upgrade run. Three members of the LIGO team are empowered to move the mirrored blocks by just the right traces in just the right way. Only they know the truth, and the test protocol is that they not reveal a planted signal until the collaboration has finished analyzing it and is ready to publish a paper and hold a press conference. “Blind tests” like this are the gold standard in all branches of science.
So we’ll just have to cool our heels. But probably not for long — a matter of weeks or months, not years.“Essential to the Process”
A premature “discovery” getting loose, and then being denied or retracted, could diminish the public’s trust in scientists — and the scientific process — in general. “We live in a crazy time when it comes to science and the public, as the ongoing ‘debate’ about climate change shows us again and again,” wrote astronomer Adam Frank (University of Rochester) in his NPR blog on the BICEP2 fiasco in 2014. “I wish they’d have let the usual scientific process run its course before they made such a grand announcement. If they had, odds are, it would have been clear that no such announcement was warranted — at least not yet — and we’d all be better off.”
Sigurdsson, however, disagrees. When the BICEP2 team announced their results, he used it as an example in his Cosmology 101 class, encouraging students to view it as an uncertain result in mid-discovery phase. “I think most of the public appreciates the fact that you can make mistakes for the right reasons and that’s part of the process,” says Sigurdsson. “We proceed by falsification. We make conjectures, we test them, and some of the time we find that things were wrong and we throw them out. But that’s still essential to the process. We need to get that across.”
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