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This Week's Sky at a Glance

Night sky sights for December 14 – 22

by Alan M. MacRobert

Friday, December 14

  • Orion stands centered between two bright lights this year. High above it during evening shines dazzling Jupiter (with its orange sidekick Aldebaran). A similar distance below Jupiter, Sirius rises around 8 p.m. (the time depends on your location), with its own sidekick, Mirzam.

    Sirius, just 8.6 light-years away, is the brightest star in the night sky. It's also the closest star beyond the Sun that's ever visible to the unaided eye from mid-northern latitudes.

  • Algol in Perseus should be at minimum light for a couple hours centered on 6:07 p.m. EST. Watch it rebrightening for much of the rest of the night.

  • Jupiter's Great Red Spot should cross Jupiter's central meridian around 8:22 p.m. EST. For all of the Great Red Spot's transit times, as well as all of Jupiter's satellite events, get our new JupiterMoons app!

    Saturday, December 15

  • In early evening, the "Summer Star" Vega is still the brightest thing in the northwestern sky, though it's moving ever lower. The brightest above it is Deneb. Vega is 25 light-years away; supergiant Deneb is about 1,400.

    Sunday, December 16

  • Jupiter's moon Io crosses Jupiter's face from 8:19 to 10:29 p.m. EST, closely followed by its tiny black shadow (much plainer to see in a telescope) from 8:41 to 10:52 p.m. EST. Meanwhile, the Great Red Spot should cross Jupiter's central meridian around 10:00 p.m. EST. To track all of Jupiter's satellite events and the Great Red Spot's transit times, get our new JupiterMoons app.

    Monday, December 17

  • The first-discovered asteroid, 1 Ceres, is at opposition tonight. It's not far from 4 Vesta, which is also in Taurus along with Jupiter. Ceres and Vesta are now magnitudes 6.7 and 6.5, respectively. Spot them in binoculars near the horns of Taurus using our finder chart in the December Sky & Telescope, page 50, or online.

    Tuesday, December 18

  • After dinnertime this week, Cassiopeia stands at its very highest in the north like a flattened M (for skywatchers at mid-northern latitudes). The Milky Way runs through it, stretching all the way down to the east horizon on one side and the west horizon on the other. Given the quality of your sky, how much of the Milky Way (if any) can you trace out?

    Wednesday, December 19

  • The first-quarter Moon shines at the dim Circlet of Pisces, below the much larger and brighter Great Square of Pegasus early in the evening.

    Thursday, December 20

  • Jupiter's moon Europa crosses Jupiter's face tonight from 9:45 p.m. to 12:07 a.m. EST, followed by its tiny black shadow (plainer to see in a telescope) from 10:40 p.m. to 1:04 a.m. EST.

    Friday, December 21

  • By about 9 p.m. (depending on where you live east or west in your time zone) the dim Little Dipper hangs straight down from Polaris, as if from a nail on the north wall of the sky.

  • Winter begins in the Northern Hemisphere at the solstice, 6:12 a.m. EST. This is the shortest day of the year. (The Earth didn't flip upside down? No continents flying loose? Some folks have all the fun.)

    Saturday, December 22

  • During the Christmas season, Sirius rises in the east-southeast, far below Orion, around 7 or 8 p.m. depending on your location. When Sirius is still low, binoculars often show it twinkling in vivid colors. All stars do this when low, but Sirius is the brightest, making the effect more pronounced.




    Want to become a better amateur astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

    For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

    Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The standards are the little Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope effectively.

    You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the beloved if dated Burnham's Celestial Handbook.

    Can a computerized telescope replace charts? Not for beginners, I don't think, and certainly not on mounts and tripods that are less than top-quality mechanically (able to point with better than 0.2° repeatability). As Terence Dickinson and Alan Dyer say in their invaluable 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, Venus, and Saturn form a long diagonal line in the southeast as dawn begins to brighten. Venus is by far the brightest, at magnitude –3.9. Look far to its upper right for Saturn, magnitude +0.7, and farther on for Spica, magnitude +1.0. Look lower left of Venus for Mercury, magnitude –0.5, now moving a little lower each day. The whole line of four points is now about 45° long.

    By week's end, use binoculars to try to spot Antares twinkling low in the dawn below Venus and to the right of Mercury, as shown above.

    Mars (magnitude +1.2, in Sagittarius) still remains low in the southwest in evening twilight. In a telescope it's just a tiny blob 4.3 arcseconds in diameter — hardly larger than Uranus!

    Jupiter (magnitude –2.8, in Taurus) is already glaring in the east as twilight fades. It climbs to dominate the eastern and high southeastern sky into the evening, with orange Aldebaran 5° below it and the Pleiades about twice as far to its upper right. Jupiter is highest in the south around 10 or 11 p.m. In a telescope it's still a big 48 arcseconds wide, essentially as large as it ever appears.

    Uranus (magnitude 5.8, in Pisces) and Neptune (7.9, in Aquarius) are the south and southwest, respectively, right after dark. 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) equals Universal Time (also known as UT, UTC, or GMT) minus 5 hours.

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