Sky & Telescope news
This month offers great variety in the night sky: planets (and a comet!) before dawn, a strong meteor shower, and a parade of bright stars after sunset.
With the solstice occurring at 11:48 p.m. Eastern Standard Time on the 21st, December offers northern observers the longest nights for stargazing all year — and there's plenty to see!
You'll find many of the best sights in the eastern sky before dawn. Venus and Jupiter are dazzling, with the bright star Spica and Mars sandwiched between them. A thin crescent Moon is perched dramatically close to Venus on December 7th. That same morning, Comet Catalina (C/2013 US10) is just a few degrees to the left of Venus, and it might be bright enough to just barely appear as a fuzzy star. Binoculars will help.
Later in the month, on the nights of December 13th and 14th, we'll be treated to the Geminid meteor shower. With moonless skies and good viewing prospects this year, you might see at least one of these "shooting stars" per minute from a dark location. A few Geminids should be obvious by 10 p.m. — but the later you stay up, the more of them you'll see.
Throughout December, you'll see bright stars parading across the sky after sunset. Vega and the Northern Cross of Cygnus are over in the west, while Orion, Taurus, and Gemini dominate the east.
To get a personally guided tour of the night-sky sights overhead during December, download our 7½-minute-long stargazing podcast below.
There's no better guide to what's going on in nighttime sky than the December issue of Sky & Telescope magazine.
Dynamicists predict that the larger of Mars's two moons will shatter to create a ring, slam into the planet — or both — in 20 to 40 million years.
The Red Planet's two moons, discovered by Asaph Hall in 1877, are small and irregularly shaped. Deimos circles every 30.3 hours from an orbit that averages 20,100 km high. Larger Phobos, only 27 km (17 miles) long, orbits just 5,980 km (3,710 miles) above the Martian surface. In fact, Phobos hovers closer to its planet than any other moon in the solar system. That's not a good thing.
Because it whips around in just 7.7 hours, compared to the 24.7 hours that Mars takes to rotate, Phobos is doomed. Thanks to a teensy tidal interaction that its gravity creates in the Martian interior, this moon is slowly losing orbital energy and moving ever-so-slowly closer to the planet. Dynamicists predict that it should drop into the Martian atmosphere in perhaps 20 to 40 million years .
Arguably, Phobos should have performed its death dive long ago. But its small size minimizes the tidal torquing inside Mars, and it likely started out just inside the altitude (20,500 km) that would have synched its orbital period with the planet's spin rate. So it's taken 4½ billion years for Phobos to migrate this far inward.
As it gets closer to Mars, the tidal forces that are inexorably building within Phobos will start to tear it apart — and maybe they already are. Earlier this month, at the American Astronomical Society's Division for Planetary Sciences meeting, Terry Hurford (NASA Goddard) presented a new analysis of the numerous grooves found in the surface of Phobos. When the Viking orbiters first imaged these in 1976, geologists assumed they were fractures radiating from Stickney, a 10-km-wide pit that takes up a sixth of the moon's circumference.
But, as Hurford and his collaborators point out, the fractures are actually mostly symmetric to the point on Phobos directly facing toward Mars. The implication is that The End has already begun. "We think that Phobos has already started to fail," Hurford says, as the moon is gradually distorted into an oblong shape. "And the first sign of this failure is the production of these grooves."
Right now the tidal forces exerted by Mars are too weak to be cracking Phobos open if its interior is solid throughout, which is how planetary scientists once envisioned this fast-moving moon. But the thinking these days is that Phobos is a big pile of rubble masked by a veneer of fine dust perhaps 100 meters thick. What's the evidence for that? The Stickney impact would have shattered a solid object, so the interior must have been at least partly fragmented when it endured that big whack. Also, the spectrum of Phobos is a dead ringer for that of the Tagish Lake meteorite, a porous carbonaceous chondrite that fell onto a frozen lake in 2000.
To Hurford and his team, all this suggests that the many grooves are akin to stretch marks created as the interior shifts around and fractures. Curiously, the pattern of grooves on the moon's northern half provides a remarkable fit to the stress calculations, yet the southern half has grooves oriented much more randomly. Some grooves appear fresher than others, implying that the tidal deconstruction of Phobos is going on now.Yet To Come: A Ring Around Mars?
The timetable for Phobos' demise depends critically on how much of a tide its gravity is creating inside Mars, and estimates for that vary. If the Martian interior is relatively "squishy," yielding stronger tides, then Phobos has at most 25 million years before its ultimate plunge. A stiffer Mars, which some researchers support, might give the moon another 70 million years.
Regardless, bad things will happen to Phobos once its orbit drops too close to the Martian surface. Exactly what will take place and when depends on the moon's interior structure, and researchers Benjamin A. Black and Tushar Mittal (University of California, Berkeley) examine the possible outcomes in the November 21st issue of Nature Geoscience.
They conclude that Phobos won't simply plunge intact into Mars. Instead, it's more likely that the moon's dusty, outer layer will stripped away first, creating a temporary ring around Mars very quickly — in just a week or so.
Depending on how much mass it sucks away from the moon, the ring might initially rival Saturn's in its particle density — but Saturn's will likely still appear brighter because its ring consists of icy bits whereas particles in a Phobos-derived ring would be nearly black. In any case, Black and Mittal calculate that, once formed, the ring could linger for anywhere from 1 to 100 million years.
Meanwhile, the solid chunks of Phobos will meet a quicker end. They'll strike the surface, creating a series of oblique craters around the planet's equator. If big pieces break apart while plunging through the atmosphere, they could strafe the surface and create chains of craters sorted in size by the fragments' masses. Then that beautiful but ephemeral ring will be all that remains of Phobos, and Deimos (out of danger thanks to its higher orbit) will become Mars' lone moon.
Friday, November 27
• Before and during dawn, Venus shines within 5° of Spica from tomorrow through December 2nd. Tomorrow morning, look also for 2nd-magnitude Gamma Virginis (Porrima) just to Mars's left, as shown here.
• Algol is at minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 7:04 p.m. EST (per new predictions).
Saturday, November 28
• By 8 or 9 p.m. the waning gibbous Moon is up in the east-northeast. It's in Gemini; look left of it and perhaps a bit higher for Castor and Pollux. Farther to the Moon's right or upper right, Orion is moving up.
Sunday, November 29
• By 10 or 11 p.m. now (depending in how far east or west you live in your time zone), the dim Little Dipper hangs straight down from Polaris.
Monday, November 30
• Two faint fuzzies naked-eye: The Andromeda Galaxy (M31) and the Perseus Double Cluster are two of the most famous deep-sky objects. They're both cataloged as 4th magnitude, and in a fairly good sky you can see each with the unaided eye. They're located only 22° apart, high in the northeast these evenings — to the right of Cassiopeia and closer below Cassiopeia, respectively.
But they look rather different, the more so the darker your sky. See for yourself. They're plotted on the all-sky constellation map in the center of the November Sky & Telescope.
Tuesday, December 1
• This evening is dark and moonless until the waning Moon rises around 11 p.m. Once the Moon is up, look for Regulus about 4° left of it (for North America). By dawn on the 2nd the Moon is under Regulus, as shown above.
Wednesday, December 2
• The last-quarter Moon rises in the east around 11 or midnight tonight. You'll find it hanging below Regulus. About 50 minutes later, Jupiter rises below the Moon. By dawn on Thursday the 3rd, the three of them stand high in the south — while Venus blazes in the southeast.
Thursday, December 3
• Jupiter and the Moon shine together after rising after midnight tonight. In early dawn on Friday the 4th, they stand paired less closely (for North America) high in the south, as shown above. By then Mars, Spica, and bright Venus shine to their lower left.
Friday, December 4
• The big Summer Triangle is still laid out the western sky after dark these cold evenings. Its brightest star is Vega, the brightest in the area. Look above Vega for Deneb. Farther to Vega's left or lower left is Altair.
• Before and during dawn on Saturday the 5th, bright Venus in the southeast anchors a diagonal line that stretches past Spica to connect Mars, the waning Moon, and then Jupiter.
Saturday, December 5
• In early dawn on Sunday morning the 6th, the waning crescent Moon hangs roughly between Mars and Spica, as shown at right.
• Advance notice: during daytime on Monday, the Moon will occult (cover) Venus for practically everyone with a telescope or binoculars in the U.S., Mexico, and Central America. See the December Sky & Telescope, page 46.
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 (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, 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.
Venus, Mars, and Jupiter continue their display in the east before and during dawn. Venus is the lowest and brightest, shining at magnitude –4.2. Jupiter, high to the upper right, is –2.0, and Mars, between them, is much fainter at +1.5.
Watch the line lengthening. Venus is descending; Jupiter and Mars are moving higher. So is Spica; watch it pass to the right of Venus this week.
Saturn is hidden in conjunction with the Sun.
Uranus (magnitude +5.7, in Pisces) and Neptune (magnitude +7.9, in Aquarius) are high in the southern sky during early evening. Finder charts for Uranus and Neptune.
All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.
Eastern Standard Time (EST) is Universal Time (UT, UTC, or GMT) minus 5 hours.
"We may be little guys, but we don’t think small. It’s the courage of questions, of grasping our true circumstances, and not pretending we are at the center of it all, that is adulthood."
— Ann Druyan, 2014
The post This Week’s Sky at a Glance, November 27 — December 5 appeared first on Sky & Telescope.
Astronomers have taken a careful census of the smallest stars in our galaxy’s center.
How many stars are out there? It’s an easy question to ask but a surprisingly difficult one to answer.
Astronomers root their response in a mathematical function that describes how many stars exist at any given mass, known as the initial mass function. In general, we know there are many more low-mass stars than high-mass ones, just as you’ll find far more fine grains of sand than large pebbles on a beach.
And just as knowing exactly how many more fine grains there are than pebbles will tell you something about how that beach came to be, stars’ initial mass function helps astronomers investigate everything from the details of star formation to the mass of the Milky Way and other galaxies.
Until now, astronomers’ best measurements of the initial mass function have been limited to relatively nearby stars, which lie within the Milky Way’s pancake-shaped disk. But other galaxies have shown tantalizing hints that the mass distribution of stars might differ from place to place within a galaxy.
Now, a recent study has applied the power of the Hubble Space Telescope to go beyond the disk and count stars within the Milky Way’s bulge, the sardine-packed collection of stars far away in the center of our galaxy.
A team led by Annalisa Calamida (Space Telescope Science Institute) reported the initial mass function for low-mass bulge stars in the September 1st Astrophysical Journal, focusing stars less massive than the Sun. The astronomers tracked stars’ proper motions across the sky using the exquisitely sharp Hubble images, then picked out the background bulge stars by their odd, boxy orbits. The result is a sample of low-mass stars with near-zero “contamination” from nearby stars.
Overall, the team’s results aren’t surprising: they estimate an initial mass function that roughly agrees with previous measurements, including one made by this author. But there are hints of something interesting afoot: the new results suggest that the bulge might contain relatively fewer very low-mass stars. More work is needed to test whether this result pans out, but if it’s real, the difference would suggest a difference in how stars form in the galactic bulge compared to the disk.
This study is an important first step in going beyond the nearby disk stars that are often observed. And there’s more to come: with the Gaia mission already at work surveying more than 1 billion stars and the Large Synoptic Survey Telescope on the way, astronomers will soon be counting stars throughout our galaxy. And the initial mass functions they measure will tell us not only how many stars are out there, but how star formation varies from place to place in our galaxy.
Is perception reality? Not when it comes to the Moon illusion. See the truth with your own eyes at the rising of the next full Moon.
Watch for the full Frost Moon to rise around sunset Wednesday night (November 25th), a perfect opportunity to witness one of the oldest psychological tricks known to humankind — the Moon illusion.
Even as far back as the 4th century B.C., Aristotle noted the apparent hugeness of the horizon-hugging Moon compared to it viewed overhead. Back then it was attributed to magnification by the atmosphere, but now we know it's all in our head. Photos of the rising and meridian moons show them as identical in size.
To see for yourself, take a sheet of paper and roll it up into a narrow tube. Point it at the rising Moon and adjust the tube's size until it's a little larger than the Moon's diameter. Tape the tube so its size stays the same and look at the Moon again a few hours later when it's higher in the sky. You'll see it fills the same space.
The illusion not only applies to the Moon but also to the constellations. Many observers have noticed this when viewing constellations near setting or rising compared to mental images of those same groups viewed higher up. Just the other night I caught sight of the trapezoid-shaped "Keystone" of Hercules setting in the northwest. It was huge! That was my first impression, but interestingly, the sensation faded the longer I looked.
The Big Dipper offers one of the best examples of constellation inflation, a phenomenon you can easily see this month and next. During early evening hours, the Dipper looms large as it arcs along the northern horizon, but seems to shrink toward dawn on its climb toward the zenith.
For as long as we've seen the illusion, people have been trying to explain why it happens. There's no question it has to do with how we perceive celestial objects in a terrestrial setting, but the particulars remain elusive. So what's going on here?
In daily experience, an object overhead, say a bird or aircraft flying by, appears closer and therefore larger than the same bird or plane near the horizon because it really is closer. We're built to think that objects near the horizon are (usually) more distant than those overhead because they appear to lie behind and beyond foreground objects.
But for extraterrestrial bodies such as the Moon, Sun and star groupings, which are identical in size whether on the horizon or at the zenith, we have no reference. Therefore, when we gaze at a horizon Moon, which clearly lies beyond every object in the foreground, our brains assume it must be farther away than the overhead version. We compensate for this perception by inflating the Moon's size. In a sense, our brains force the Moon to meet our expectations of how big it should be.
This perception is reinforced by yet another perception — how we see the shape of sky. Lots of us look up and imagine the sky as a flattened dome with the zenith relatively nearby and the horizon in the far distance. Our mental muscle miscalculates the Moon's distance, imagining it to be much farther off compared to its overhead distance, which brings us back to the size-forcing issue. The flattened sky perception may help explain why some airline pilots report seeing a bloated, low Moon in an empty sky with no reference but the horizon.
Our brains happily create powerful illusions from the moment we wake up in the morning. Think of all the rectangular and square objects we come across during the day. Unless you're staring square-on at these shapes, they should look like trapezoids of all dimensions. Do they? No — our brains still see them as squares and rectangles even when viewed up close from the side. Crazy!
What's funny in all of this is that the rising Moon is actually 1.5% smaller than when it's overhead because we have to look across the radius of the Earth — or just under 4,000 miles — at rising time. With the Moon near the zenith, we look straight into space with no Earth in the way. Perhaps the solution to the illusion lies in a mashup of perceived distance, our internal model of the sky, and the Ponzo illusion.
Other explanations abound, proving that a complete solution remains a moving target. Take a look for yourself the next few nights when the frosty Moon climbs above the eastern horizon.
Find a spot with a busy foreground and compare that impression to one made in a simpler setting where you can easily block out the foreground to show an isolated Moon relatively close to the horizon. Do both perspectives swell the Moon's apparent size equally? Then look at the Moon when it's high in the sky and recall its rising appearance. Does it look obviously smaller?
Whether you perform these simple experiments or just feel like basking in the brilliance of the November Moon, click here for moonrise times for your location. And don't forget to watch the full Moon occult Aldebaran early Thanksgiving morning (November 26, 2015) across much of the U.S. and Canada. Talk about illusions. You'll be watching the puny 2,160-mile-diameter Moon cover a star nearly 18,000 times its size.
Need a map to go with that Moon? Check out the Sky & Telescope Field Map of the Moon!
Astronomers have spotted what appears to be a regular signal coming from the blazar known as PG 1553+113.
Observing a blazar is a little like standing beneath a relativistic waterfall. Look up: that flickering point of light is a head-on view of the powerful plasma jet shooting out from a supermassive black hole.
The free-flying electrons within that mess of plasma twirl at almost light speed around magnetic fields, and they radiate across the electromagnetic spectrum, often drowning out any other forms of emission. We might even see a sudden outburst when turbulence, a sudden influx of plasma, or some other force roils the jet.
But when Markus Ackermann (DESY, Germany) and colleagues pored through almost seven years of data collected with the Fermi Gamma-Ray Space Telescope, they saw something completely unexpected: a regular signal coming from a blazar. Gamma rays from PG 1553+113 seem to brighten roughly every 2.2 years, with three complete cycles captured so far.
Moreover, other wavelengths seem to echo this cycle. Inspired by the gamma-ray find, Ackermann’s team sought out radio and optical measurements from blazar-monitoring campaigns — and both wavelengths show hints of the same periodic signal. The team also looked at X-ray data collected over the years by the Swift and Rossi X-ray Timing Explorer spacecraft, but there weren’t enough data points for a proper analysis.
If this signal is real, it has to come from the black hole-powered jet, and the authors explore a number of explanations.
For example, the jet might be precessing or rotating, sweeping its beam past Earth every 2 years or so. Or perhaps a strong magnetic field chokes the flow of gas toward the black hole, creating instabilities that then regularly flood the jet with material. The most intriguing prospect is another supermassive black hole in the system, its presence affecting gas flow and jet alignment.
At this point, though, the authors admit they don’t have enough data to distinguish between these possibilities. Further monitoring might remedy that.Keep Watching
“I am always skeptical about claims of periodicity based on only 2 to 3 cycles,” says Alan Marscher (Boston University), a blazar expert not involved in the study. Even completely random processes, he adds, can create apparently regular signals over short periods of time.
And Ackermann’s team is frank about the data’s limits. After all, blazars are known to flare randomly and, due to the length of the suspected cycle, only three complete periods have been captured so far. The authors estimate a few percent probability that this signal is indeed a chance alignment of random flares.
Still, the fact that the signal is observed across radio, optical, and gamma rays strengthens the case. “Seeing such well-correlated oscillations across the different wavebands isn't as common as simple models would expect,” Marscher notes.
“It's worth keeping an eye on this object.”
Curious about black holes? Download our FREE ebook and learn how the supermassive beasts have shaped our universe.
Mattatuck Astronomical SocietyADDRESS
21 Rek Lane
Connecticut 06712 USA
email@example.comURL NUMBER OF MEMBERS OTHER INFORMATION
Farpoint Astronomical Research
11358 Amalgam Way, Suite A1, Gold River, CA 95670
877-623-4021 or 916-671-5735
Farpoint introduces the “D” Series Dovetail Camera Mount Quick Release Adapter ($55). This piggyback bracket connects any camera or accessory that uses a 1⁄4-20 threaded mount to Losmandy D-size dovetail plates, allowing you to quickly reconfigure your telescope with secondary cameras, guide scopes, or other additional accessories. The adapter is manufactured from anodized aluminum and includes easy-grip knobs that can be operated while wearing gloves (dovetail plate not included).
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.
With a little guidance, you can pick a high-quality telescope that can last a lifetime. S&T: Craig Michael Utter Here's a quick guide to help you make sense of all the types of telescope models available today. Armed with these few basics, you'll have a good idea what to look for (and what to avoid) when scouring the marketplace for your new scope.
If you still have questions or need more details, check out these additional resources:
- Telescope buyer's guide (online article)
- "What to Know Before You Buy" (PDF) from SkyWatch 2010
- Guide to Buying Your First Telescope (video) from Sky & Telescope's Skywatching Video Series
Many (arguably most) good starter scopes cost $400 or more, though some superb choices are available for under $250. But read this article first, so you'll understand the terminology and what type of telescope will be best for you.
The telescope you want has two essentials: high-quality optics and a steady, smoothly working mount. And all other things being equal, big scopes show more and are easier to use than small ones, as we'll see below. But don't overlook portability and convenience — the best scope for you is the one you'll actually use.Aperture: A Telescope's Most Important Feature
The most important characteristic of a telescope is its aperture — the diameter of its light-gathering lens or mirror, often called the objective. Look for the telescope's specifications near its focuser, at the front of the tube, or on the box. The aperture's diameter (D) will be expressed either in millimeters or, less commonly, in inches (1 inch equals 25.4 mm). As a rule of thumb, your telescope should have at least 2.8 inches (70 mm) aperture — and preferably more.
Dobsonian telescopes provide lots of aperture at relatively low cost. S&T: Craig Michael Utter A larger aperture lets you see fainter objects and finer detail than a smaller one can. But a good small scope can still show you plenty — especially if you live far from city lights. For example, you can spot dozens of galaxies beyond our own Milky Way through a scope with an aperture of 80 mm (3.1 inches) from a dark location. But you'd probably need a 6- or 8-inch telescope like the one shown at right to see those same galaxies from a typical suburban backyard. And regardless of how bright or dark your skies are, the view through a telescope with plenty of aperture is more spectacular than the view of the same object through a smaller scope.
Avoid telescopes that are advertised by their magnification — especially implausibly high powers like 600×. For most purposes, a telescope's maximum useful magnification is 50 times its aperture in inches (or twice its aperture in millimeters) . So you'd need a 12-inch scope to get a decent image at 600×. And even then, you'd need to wait for a night when the observing conditions are perfect.Types of Telescopes
You'll encounter three basic types of telescopes:The three basic telescope designs use different optics to achieve the same result: making distant objects look bigger and brighter than they appear to your eye. See the text for links to animations that show how light passes through the optics of each design. S&T: Gregg Dinderman
• Refractors have a lens at the front of the tube — it's the type you're probably most familiar with. While generally low maintenance, they quickly get expensive as the aperture increases. Watch an animation of light passing through a refractor.
• Reflectors gather light using a mirror at the rear of the main tube. For a given aperture, these are generally the least expensive type, but you'll need to adjust the optical alignment periodically — especially if you bump it around a lot.Watch an animation of light passing through a reflector.
• Compound (or catadioptric) telescopes, which use a combination of lenses and mirrors, offer compact tubes and relatively light weight; two popular designs are called Schmidt-Cassegrains and Maksutov-Cassegrains. Watch an animation of light passing through a compound telescope.
The objective's focal length (F or FL) is the key to determining the telescope's magnification ("power"). This is simply the objective's focal length divided by that of the eyepiece, which you'll find on its barrel. For example, if a telescope has a focal length of 500 mm and a 25-mm eyepiece, the magnification is 500/25, or 20x. Most types of telescopes come supplied with one or two eyepieces; you change the magnification by switching eyepieces with different focal lengths.The Mount: A Telescope's Most Under-Appreciated Asset
Your telescope will need something sturdy to support it. Many telescopes come conveniently packaged with tripods or mounts, though the tubes of smaller scopes often just have a mounting block that allows them to be attached to a standard photo tripod with a single screw. (Caution: A tripod that's good enough for taking your family snapshots may not be steady enough for astronomy.) Mounts designed specifically for telescopes usually forgo the single-screw attachment blocks in favor of larger, more robust rings or plates.
For all their apparent diversity, telescope mounts boil down to two basic types. An alt-azimuth mount (left) permits the scope to move up-down and left-right. Itâ€™s quick to set up and intuitive to use. An equatorial mount (right) can track celestial objects by turning just one axis and can be more easily motorized — but to work properly it must be aligned with Polaris, the North Star. S&T: Craig Michael Utter On some mounts the scope swings left and right, up and down, just as it would on a photo tripod; these are known as altitude-azimuth (or simply alt-az) mounts. Many reflectors come on an elegantly simple wooden platform, known as a Dobsonian, that's a variation of the alt-az mount. A more involved mechanism, designed to track the motion of the stars by turning on a single axis, is termed an equatorial mount. These tend to be larger and heavier than alt-az designs; to use an equatorial mount properly you'll also need to align it to Polaris, the North Star.
Some telescopes come with small motors to move them around the sky with the push of a keypad button. In the more advanced models of this type, often called "Go To" telescopes, a small computer is built into the hand control. Once you've entered the current date, time, and your location, the scope can point itself to, and track, thousands of celestial objects. Some "Go To"s let you choose a guided tour of the best celestial showpieces, complete with a digital readout describing what's known about each object.
But Go To scopes aren't for everyone — the setup process may be confusing if you don't know how to find the bright alignment stars in the sky. And lower-priced Go To models come with smaller apertures than similarly priced, entry-level scopes that have no electronics.Remember . . .
Any telescope can literally open your eyes to a universe of celestial delights. With a little care in selecting the right type of telescope for you, you'll be ready for a lifetime of exploring the night sky!
An ultra-deep survey has turned up a sizable object situated nearly 10 billion miles from the Sun — more distant than any known solar-system object.
Prowling the outer Kuiper Belt for large, distant members of our solar system has turned up a zoo of remarkable finds in recent years. There's Eris, for example which triggered a divisive debate about Pluto's planetary status; Sedna, whose orbit carries it out to more than 900 astronomical units (1 a.u. is the mean Earth-Sun separation); and 2007 OR10, the record-holder for most distant object (87 a.u.) when found.
But at last week's meeting of the American Astronomical Society's Division for Planetary Sciences, Scott Sheppard (Carnegie Institution for Science) announced that he, Chad Trujillo (Gemini Observatory), and David Tholen (University of Hawai'i) have spotted something even farther from the Sun. This body, designated V774104 for now, lies 103 a.u. away in the direction of east-central Pisces — that's 9.6 billion miles or 15.4 billion km.
The object turned up in a pair of images taken October 13th with Japan's 8-meter Subaru Telescope atop Mauna Kea. The animation at upper right shows the motion of V774104 in the 5½-hour interval between the two images. "We detect the motion of solar system objects by parallax and not by the actual movement of the object," Sheppard explains. An object around 100 a.u. away will shift about 1.3 arcseconds per hour, he says, so it's easily detected in a few hours.
V774104 is so distant that it will take another year of study to determine its orbit. "All we really know is the distance," Sheppard admits, along with a guess as to its size. Given its brightness — just 24th magnitude — and assuming that its surface is 15% reflective, the object might be 500 km across. The researchers will make follow-up observations in early December with one of the 6.5-m Magellan telescopes in Chile.What Kind of Orbit?
Dynamicists will be eager to learn what kind of orbit V774104 occupies. A highly eccentric track would mean that it periodically swings much closer to the Sun. That's the case with Eris, which likely got flung into its 558-year-long orbit after a gravitational encounter with Neptune eons ago.
But if the orbit is more circular, or if V774104 was found near perihelion, then it's completely decoupled from the massive planets — and that will cause dynamicists to question how it got out there. Two other distant objects, Sedna and 2012 VP113, are also in this kind of orbital limbo. There's no consensus on why they're out there; possible causes run the gamut from gravitational stirring of the even more distant Oort Cloud by a close-passing star to the presence of an undiscovered massive planet far beyond the orbit of Neptune. Or they might be the first-found members of the inner Oort Cloud.
Meanwhile, the search goes on for Sheppard, Trujillo, and Tholen. They're using the Subaru Telescope and the 4-m Blanco Telescope at Cerro Tololo Inter-American Observatory to conduct the largest, deepest survey to date for distant solar-system objects. They hope to find more Sedna-like objects — and Sheppard tells me they've spotted several more objects lying 80 to 90 a.u. away that are being tracked. Should all of these turn out to share orbital characteristics, it would imply that a massive planet awaits discovery in the distant solar system.