Sky Talk January 2012: The Astronomy of 2012: Fact vs. Fiction

With so much hype and misinformation concerning the year 2012 currently in books, on television, in movies, and the subject of various conferences, this month’s column is designed to hopefully bring some science and common sense to this sensational topic as we begin the much-heralded year marking the end of the fabled Mayan calendar.

Let’s begin by asking just what’s so special about the “Galactic Alignment” we’re hearing so much about? Nothing! Every year on or about December 21st the Sun “aligns” with the center of our Milky Way Galaxy at the Winter Solstice. Supposedly it’s going to be more closely lined up than in recorded history. Yet, as is well-known to astronomers, it was actually closer to the center in 1998! (This stems from the subtleties of the galactic and ecliptic coordinate systems, which space prohibits covering here.) But in any case, the Sun will still be several degrees from being exactly over the galactic center in 2012. Even more significant is the fact that the alignment is only an apparent one—the actual center of our Galaxy is 26,000 light-years away (that’s 26,000 x 6,000,000,000,000 miles!). There can be no sudden drastic influx of radiation precisely at midnight on the 21st from the nucleus’ black hole devastating the Earth’s population, as is being claimed by some—nor will we be sucked in as others fear!

There’s also the “Great Dark Rift” that’s being talked a lot about as a kind of “roadway” into the center of the Galaxy. What’s being referred to is one of the many areas of dark obscuring clouds of gas and dust that line the spiral arms of the Galaxy. And there are at least six of these arms, with our Solar System here in the galactic boondocks being imbedded in an outer one. The dark rift seen in the summer and fall Milky Way in our local arm does not lead to the center of the Galaxy!

The thing that really puzzles me the most about the 2012 fiasco, as an astronomer, concerns the planet Venus. As the third brightest object in the sky after the Sun and Moon, this radiant orb held great importance to the Maya. And yet a very rare and spectacular event involving Venus that will occur during 2012 has been largely ignored by 2012 writers and speakers. On the late afternoon of June 5th, Venus will transit the face of Sun—an event that can be seen even with the unaided eye! (The transit will be featured in the June installment of Sky Talk along with tips on safely viewing it.) This happens in pairs separated by 8 years—the last having occurred in 2004—and then not again for more than a century (2117 being the next one)! Surely the Maya attached great significance to this spectacle. Should we not also?

I would like to conclude on a positive note about 2012. Raising public consciousness of the universe and our place in it as citizens of our home Galaxy is definitely happening because of all the attention being focused on 2012. This in turn leads to that “cosmic perspective” that my late friend and mentor Carl Sagan always talked about and felt was crucial to our survival as a species. In that sense, this year of 2012 is indeed significant.

—James Mullaney
Former assistant editor at Sky & Telescope magazine and author of eight books on stargazing.

Sky Talk November 2011: Jupiter (and Its Belt) Returns!

Brilliant Jupiter is now well-placed in the eastern evening sky and once again has a surprise in store for telescope users. As reported here last year, the giant planet lost one of its two main equatorial belts (while its famed Great Red Spot increased in prominence after being nearly invisible for some time). But the belt is back! And adding to the show are Jupiter’s four bright moons waltzing around the planet from night-to-night. All you need to see the action for yourself is a clear sky and a good telescope.
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Sky Talk October 2011: A Meteor Shower & Two Planets

Orionids Meteor Shower

Orionids Meteor Shower Lights Up the Sky by NASA's Marshall Space Flight Center on Flickr

Skywatchers have an ideal opportunity this month to see one of the most reliable annual displays of “shooting stars” plus the rising of the two brightest planets on opposite horizons. And all this couldn’t happen at a better time, for October typically has not only some of the best skies of the year for viewing but also on average the greatest number of clear nights.

The Orionid Meteor Shower will provide another fine display of celestial fireworks as it reaches peak activity during the evening hours of the 21st into the morning of the 22nd, maximum itself coming sometime before dawn. The Moon will interfere somewhat after midnight, being just two days past Last Quarter. As many as two dozen shooting stars will be seen under good sky conditions (or about one every two minutes).
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Sky Talk September 2011: Spotting Uranus

We’ve discussed all five of the bright naked-eye planets (Mercury, Venus, Mars, Jupiter, and Saturn) in this column frequently over the years but never the outer ones due to their remoteness and dimness. However, this month we go deep into the solar system to find Uranus. Seeing it for the first time is guaranteed to excite you—and bring with it a sense of great accomplishment as an observer.

Let’s begin with a few facts about Uranus itself. It was the first planet ever discovered (the other five having been known since antiquity) by the great astronomer Sir William Herschel with his homemade 6.2-inch reflecting telescope in 1781. (It turns out that Galileo actually saw Uranus much earlier with his primitive little refractor but failed to recognize it as such.) Lying some 1.8 billion miles from the Sun (twice as remote as Saturn), its visibility at such a great distance is partly due to its size—nearly four times the diameter of our Earth.
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Sky Talk August 2011: The Great White Way

New York City’s famed “Great White Way” is not the only thoroughfare to be so named. There’s a far richer and vaster one visible from anywhere on the planet — and it’s found in the Summer sky! We’re referring to the Milky Way, the grand thoroughfare of our home Galaxy. And August is one of the best times of the year to see and experience its magnificence.

Most readers know that we’re living in a vast spiral galaxy called the Milky Way. Some 100,000 light-years across, it’s about 15,000 light-years thick at its central hub and tapers off to as little as 5,000 light-years at its very edge. We’re located about two-thirds of the way out from its center located in the direction of the constellation Sagittarius. On Summer nights we are looking into its thickest and riches regions, while in Winter we’re facing the opposite direction and seeing its thin outer portions — with the result that our Galaxy is much less obvious and striking during that season. (In Spring and Fall, the Milky Way lies along the horizon and we look out at right angles to its long dimension into intergalactic space itself.)
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Sky Talk July 2011: Saturn’s Last Harrah

July offers the final opportunity this year to view the magnificent ringed planet Saturn while still well-placed above the southwestern horizon. And thanks to a famous technique using the Big Dipper as a guide to constellation identification, it’s easier than ever to identify! Plus there’s an added bonus: while a telescope is needed to see the planet’s rings themselves, thanks to its proximity to a prominent star there’s also something here for naked-eye and binocular skywatchers as well.

Right after darkness falls on July evenings, golden Saturn graces the southwestern sky as it nears the end of this year’s apparition. The brighter planets are easy to identify not only because of their prominence in the sky but also because they don’t twinkle like stars do. (See the June 2008 installment of Sky Talk.) But right now there’s also a fascinating way to identify the ringed planet even from the heart of a light-polluted city. It uses the well-known phrase “Follow the arc to Arcturus.” This refers to following the curve of the Big Dipper’s handle downward in the sky to the radiant orange star Arcturus in the constellation Bootes. And continuing that arc also brings you to the bright bluish star Spica in Virgo.
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Sky Talk June 2011: Some Frequently-Asked Questions About the Moon

Although it’s the most readily visible (aside from the Sun itself) and nearest to us of all celestial bodies, the Moon poses puzzling questions to many people — especially those new to the hobby of skywatching. Here are some of the most often asked ones.

Q: Why is the First Quarter Moon as shown on calendars actually half full?
A: The answer here is quite simple. When the Moon appears half-illuminated or half-full, it’s one quarter of the way around its monthly orbit. Likewise, at Last Quarter it’s three quarters of the way around. Yes, simple — but still very confounding terminology indeed!

Q: Why is the Full Moon so much brighter than the First Quarter one?
A: You would expect it to be twice as bright since there’s twice the area reflecting the Sun’s light back down to us. But the Moon when full is actually 12 times brighter! The reason here is not so simple: when at its quarters phases, the Sun is shining almost horizontally at a glancing angle along the surface (especially near the terminator, or dividing line between light and dark), casting very long shadows from surface features ranging from mountains and craters to boulders and even small rocks and pebbles. All those shadowed areas reflect little or no light. But when full, the entire surface of the Moon is bathed in direct sunlight and reflected our way — there are no shadows. This explains why the best times to observe our lovely satellite with binoculars and telescopes are around the quarters when surface relief is strikingly exaggerated by shadows. The Moon when full looks flat and bland — sadly disappointing many new to observing who expect to see jagged mountain ranges and deep craters!

Q: Is there really a dark side to the Moon?
A: Yes – and no! As the Moon orbits the Earth, its entire surface is illuminated by sunlight at one time or another, back as well as front. Known as “complimentary phases,” this means that when the Moon is full to us, its back side is totally dark. When the Moon is new and dark to us, the back is bathed in direct sunlight. In between, the back side experiences the compliment of whatever phase we are seeing. When a crescent to us, it appears gibbous there. At the quarters, both front and back are equally half illuminated.

Q: If the Moon rotates, why do we never see the back side?
A: That’s because the Moon rotates in the same period as it revolves around the Earth. To see this, stand in the middle of a room and have someone face you several feet away. Now, ask them to slowly move around you while always facing in the same direction (which means they are not rotating on their “axis” but only revolving in their “orbit” around you). As you follow their movement, you’ll first see the side of their face and then the back of their head! If the Moon didn’t rotate, we would see the back side just as in this example.

–James Mullaney
Former assistant editor at Sky & Telescope magazine and author of eight books on stargazing.

Sky Talk May 2011: Predawn Planetary Conclave

Those of you who don’t mind rising early in the morning will have a special treat this month as you look toward the eastern sky before dawn. There you’ll find a grouping of four of the major planets — and a spectacular close approach of the two brightest ones!

For a week or so around the morning of May 11th, radiant Venus and slightly fainter Jupiter will grace the eastern sky about an hour before sunrise. On that date itself the two planets will be just half a degree — or a Moon’s width — apart, creating a stunning sight even with the naked-eye. In binoculars the view both then and for several days on either side of the 11th will be truly spectacular! Watch these worlds slowly close together and then move apart over a period of days. For those fortunate enough to own a low-power, wide-field telescope like the Edmund Astroscan Plus, not only will the view be even more of a spectacle with brighter images than binoculars can deliver but at magnifications of just 20x to 30x the little disks of both planets will be visible. (Due to atmospheric turbulence this close to the horizon, don’t expect the images to be sharp. But both objects will be definitely non-stellar.)

Two additional but much less bright and obvious planets lie nearby around this time. As seen during the interval 60 minutes to 30 minutes before sunrise, elusive Mercury will appear between 1.5 and 2 degrees to the lower right of Venus and ruddy Mars will be positioned closer to the horizon some 5 degrees to the east of Jupiter. Seeing them with the unaided eye in the brightening twilight will be a challenge but both should show up well in binoculars. In wide-angle glasses having at least a 6-degree field, it will actually be possible to see all four planets in the same field of view when bunched closest together! In a telescope, Venus and Jupiter can be followed all the way up to (and beyond) sunrise itself. But extreme caution is needed here so that the scope isn’t accidentally turned onto the blazing Sun. As an aside, on the morning of May 1st, a lovely crescent Moon will grace the sky just above Jupiter. And by the 29th, one orbital revolution of the Earth later, the crescent Moon will again be near Jupiter. The sky is indeed a stage on which celestial drama continuously plays out to the delight of skywatchers!

In closing, we must not neglect to mention that magnificent golden Saturn is well placed for viewing during the evening in May. Look for it halfway up the southern sky, to the upper right of the bright bluish star Spica. Note that Saturn doesn’t twinkle — but Spica certainly does! For the reason why, see the Sky Talk column for June 2008. (All the previous installments are archived on the Edmund Scientifics web blog.)

–James Mullaney
Former assistant editor at Sky & Telescope magazine and author of eight books on stargazing.

Sky Talk April 2011: Binoculars for Stargazing

Many books and articles have been written over the years extolling the pleasures of stargazing using binoculars, all based on the premise that “two eyes are better than one.” And indeed they are! Every major class of celestial wonder from the Moon and planets to star clusters, nebulae and galaxies lie within reach of even the humblest glasses. But some are better suited than others for the purpose, and knowing something about their specifications will help in selecting a pair.

Two primary parameters of a binocular are its aperture and its magnification. Those most often used for sky viewing have objective lenses 35mm or 50mm in diameter. Ones much larger in size are difficult to hold steady and require tripod mounting, while mini-binocs really don’t pull in enough light for celestial viewing. The magnification most typically found on stargazing glasses is either 7x or 10x; thus a 7×50 binocular has objectives about 2-inches in diameter and provides 7 power. This famed “night glass” (as it’s often called) is the one typically recommended for stargazing. But while certainly very serviceable, this is not the optimum combination due to an important factor known as the exit pupil.

The exit pupil relates to that of both a binocular and the opening of the human eye. In the former case, the diameter of the bundle of light emerging from a binocular’s eyepieces is found by dividing the aperture by the magnification. Thus a 7×50 glass has exit pupils 7mm in size. In the case of the eye, the exit pupil is often given as 7mm in size if fully dark-adapted. But in reality that’s rarely the case. As people age, the pupil does not open as wide as when they were younger. And any ambient light from various sources of light-pollution (so prevalent in today’s world) around the observer also contracts the pupil. In practice, 5mm diameter exit pupils are more typically found when viewing the night sky. So some of the light of a 7×50 binocular is not able to enter the eye and wasted, while the 5mm pupils provided by a 7×35 or 10×50 glass allow full use of their objectives’ light-gathering power — making either ideal for stargazing.

In actual practice, 10×50 glasses have a decided advantage. Not only do they pick up more light and offer somewhat better resolution due to their larger objectives, but that extra 3x of power is enough to tease more detail from their images. As an example, the satellites of Jupiter (depending on where they are in their orbital dances about the planet) can be glimpsed in a 7×50 binocular but stand out much better in a 10×50.

The subject of binoculars is a vast one and space prohibits covering such matters as wide-angle and extra-wide-angle glasses, porro-prism verses roof-prism designs, and image-stabilized and zoom binoculars. But there is one other feature of binocular stargazing that simply must be mentioned. And that is using both eyes gives an amazing sense of depth perception or 3-dimentionality to what’s seen! Just look at how the Moon appears to be suspended in space — especially during a lunar eclipse, or when it glides across (or occults) a glittering star cluster like the Pleiades. While simply a physiological illusion, it’s nonetheless quite spectacular!

(See Edmund’s binocular category to browse their selection.)

–James Mullaney
Former assistant editor at Sky & Telescope magazine and author of eight books on stargazing.