This Week's Sky at a Glance, December 24 – January 1

FRIDAY, DECEMBER 24

■ The line of Jupiter, Saturn, and Venus in the southwest at dusk continues to evolve. Venus, the lower right end of the line, is dropping away rapidly. And the whole line is sliding farther to the lower right. Meanwhile, Mercury down below is on its way up to pass Venus.

SATURDAY, DECEMBER 25

■ High above Orion these holiday nights shines orange Aldebaran with the large, loose Hyades cluster in its background. Binoculars are the ideal instrument for this cluster given its size: its most prominent stars (4th and 5th magnitude) span an area about 4° wide. Higher above, the brightest stars of the Pleiades span hardly more than 1°.

The main Hyades stars famously form a V. It's currently lying on its side, open to the left. Aldebaran forms the lower of the V's two tips.

With binoculars, follow the lower branch of the V to the right or upper right from Aldebaran. The first thing you come to is the House asterism: a pattern of stars like a child's drawing of a house with a peaked roof. The house is currently upright and bent to the right like it got pushed.

The House includes three binocular double stars that form an equilateral triangle, with each pair facing the center. The brightest pair is Theta¹ and Theta² Tauri. You may find that you can resolve the Theta pair with your unaided eyes.

For more, see "The Noble Hyades" by Fred Schaaf in the January Sky & Telescope, page 45.

SUNDAY, DECEMBER 26

■ This is the time of year when Orion shines in the east-southeast after dinnertime. He's well up now, but his three-star Belt is still nearly vertical. The Belt points up toward Aldebaran and the Pleiades even higher. In the other direction, it points down to where bright Sirius will rise around 7 or 8 p.m. to twinkle furiously.

■ Last-quarter Moon (exactly so at 9:24 p.m. EST). The Moon rises around midnight tonight, in Virgo. By early dawn Monday morning it shines high in the south, with Spica to its lower left and Arcturus much farther to its upper left.

MONDAY, DECEMBER 27

■ The constellation figure of Orion has only a tiny, pea-brained head: 4th-magnitude Lambda Orionis and its two fainter little companions, Phi¹ and Phi². Binoculars show them well. Did you know they're part of a sparse, loose open cluster named Collinder 69? Good binoculars under a dark sky may show a dozen of its members thinly scattered over an area 1° or more across. Astronomers have identified about 100 in all. See Matt Wedel's "Head of the Hunter," his Binocular Highlight column in the January Sky & Telescope, page 43.

TUESDAY, DECEMBER 28

■ The Pleiades shine very high in the southeast far above Orion. They're about the size of your fingertip at arm's length. How many can you count with your unaided eyes? Take your time and keep looking. Most people can count 6. With sharp eyesight, a good dark sky, and a steady gaze, you may be able to make out 8 or 9.

WEDNESDAY, DECEMBER 29

■ Sirius and Procyon in the balance. Sirius, the Dog Star, rises low in the east-southeast by about 7 or 8 p.m., depending on your location. Procyon, the Little Dog Star, shines in the east about two fist-widths at arm's length to Sirius's left.

But directly left? That depends. If you live around latitude 30° (Tijuana, New Orleans, Jacksonville), the two canine stars will be at the same height above your horizon soon after they rise. If you're north of that latitude, Procyon will be higher. If you're south of there, Sirius will be the higher one. Your eastern horizon tilts differently with respect to the stars depending on your latitude.

THURSDAY, DECEMBER 30

■ Algol should be at its minimum brightness this evening, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 10:11 p.m. EST; 7:11 p.m. PST.

■ As dawn brightens on Friday morning, look low in the southeast for the waning crescent Moon lighting the way to Mars and slightly-brighter Antares, as shown above. Compare their colors. Can you detect a difference? The name "Antares" is from the Greek for rival of Mars.

Does Mars twinkle less than Antares? A planet isn't normally supposed to twinkle — because it presents an extended surface area, each point of which twinkles somewhat independently of the others so the total averages out steady. But Mars is only 4 arcseconds wide now, tinier and more similar to a pointlike star than any of the other bright planets ever get.

FRIDAY, DECEMBER 31

■ After the noise and cheering at the turning of midnight tonight, step outside into the silent, cold dark. Shining high in the south will be Sirius, with the other stars of Canis Major to its right and below it. Sirius is the bottom star of the bright, equilateral Winter Triangle. The others are Betelgeuse in Orion's shoulder to Sirius's upper right, and Procyon the same distance to Sirius's upper left. The Triangle stands upright, just about in balance. Happy New Year.

No Moon or planets grace the midnight sky.

SATURDAY, JANUARY 1

■ As we enter January, the bowl of the Little Dipper hangs straight down from Polaris around 8 or 9 p.m., as if from a nail on the cold north wall of the winter sky.

The brightest star of the Little Dipper's dim bowl is Kochab at the bowl's lip. It's the equal of Polaris. Kochab passes precisely below Polaris around 8 p.m., depending on how far east or west you live in your time zone.

 

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This Week's Planet Roundup

Mercury is coming up from the sunset to pass Venus. On the 24th look for Mercury 9° below Venus; by the 28th it's passing 4° to Venus's lower left; and on the 31st you'll find it 7° to Venus's left or upper left. All week, Mercury remains a bold magnitude –0.7.

Venus, magnitude –4.5, rapidly sinks toward the west-southwest horizon day by day, on its way to conjunction with the Sun January 8th. Venus sets around the end of twilight on Christmas and during late twilight by New Year's.

In a telescope Venus is a dramatically thin crescent, thinning more each day. Get your scope on it as early as you can, even in the blue daytime before sunset. This week we see its crescent enlarge from 55 to 60 arcseconds tall while thinning from 8% to only 2% lit!

Mars, far and faint at magnitude +1.6, is passing Mars-colored Antares very low in the southeast in early dawn. Look for them far below high Arcturus. Antares is the brighter of these two orange dots, at magnitude +1.1. On Christmas morning Mars is 5° above or upper left of Antares. By New Year's, Mars is 6° to the star's left.

Mars is on the far side of its orbit from us, so in a telescope it's just a tiny fuzzblob 4 arcseconds wide.

Jupiter, magnitude –2.1 in Aquarius, shines in the south-southwest at dusk about three fists at arm's length upper left of Venus. It's only 36 arcseconds wide now, so don't be too disappointed by the view in a telescope.

Saturn, in Capricornus, is nearly midway between Jupiter and Venus. At magnitude +0.7, Saturn is 1/13 as bright as Jupiter.

Saturn sets about an hour after dark. Jupiter follows it down about 1½ hours later.

Uranus (magnitude 5.7, in Aries north of the head of Cetus) is very high in the southeast in early evening. See Bob King's story and finder chart.

Neptune (magnitude 7.9, in Aquarius) is less high in the south-southwest after dark.

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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 and graphics that also depend on longitude (mainly Moon positions) are for North America.

Eastern Standard Time, EST, is Universal Time (also called UT, UTC, GMT, or Z time) minus 5 hours.

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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, published by the American Astronomical Society.

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 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. The next up, once you know your way around, are the even larger Interstellarum atlas (stars to magnitude 9.5) or Uranometria 2000.0 (stars to magnitude 9.75). And be sure to read How to Use a Star Chart with a Telescope.

You'll also want a good deep-sky guidebook, such as the big Night Sky Observer's Guide set (2+ volumes) 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. And 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."

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Audio sky tour. Out under the evening sky with your
earbuds in place, listen to Kelly Beatty's monthly
podcast tour of the heavens above. It's free.

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"The dangers of not thinking clearly are much greater now than ever before. It's not that there's something new in our way of thinking, it's that credulous and confused thinking can be much more lethal in ways it was never before."
            — Carl Sagan, 1996

"Facts are stubborn things."
            — John Adams, 1770