This Week's Sky at a Glance
Some night sky sights for December 27 January 4
Friday, December 27
Saturday, December 28
Sunday, December 29
Often you read that the Great Orion Nebula, partway down the sword, looks to the naked eye like a slightly fuzzy star. Well, maybe. To start with you need sharp (or fully corrected) distance vision. You also need a good sky — and light pollution doesn't seem to be the whole story here. On some nights in the suburbs I can see the nebula around the 5th-magnitude stars Theta-1 and Theta-2 Orionis fairly positively. On other nights with the same light pollution, not so much. How about you?
Monday, December 30
Tuesday, December 31
Wednesday, January 1
The sighting will probably be impossible from the East Coast, where the Moon will be just 11 hours old and only 7° from the Sun a half hour after sunset. But it might be possible through a telescope in the Central time zone if the air is very clear. It should be possible with binoculars on the West Coast, where the Moon will be approximately 14 hours old and 8.5° from the Sun. Figure its age from the time of new Moon: 11:14 UT (3:14 a.m. Pacific Standard Time).
Go out early to mark where the Sun sets, then set up your equipment and start watching no more than 15 minutes after sundown. Keep watching for another 25 minutes to catch your window of best visibility, which will depend on your location and atmospheric conditions. For more on this pursuit, see Seeking Thin Crescent Moons.
Friday, January 3
Saturday, January 4
Hint: "Procyon" means "Before the Dog." That tells you something about where its namers lived.
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. 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 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, 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 not on mounts and tripods that are less than top-quality mechanically (able to point with better than 0.2° repeatability, which means heavy and expensive). 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 is hidden in conjunction with the Sun.
Venus (about –4.5) is dropping lower in evening twilight every day. Look southwest. Optical aid shows it becoming an ever thinner crescent: from 7% sunlit on December 27th to just 2% lit on January 4th. But it's big! —about 59 arcseconds in diameter. Good binoculars will show its crescent shape in twilight.
The best time to observe Venus in a telescope is well before sunset. Hide the Sun behind a building so you can't accidentally sweep it into your view. Read our article, See Venus's Thin Crescent. Venus is heading to inferior conjunction with the Sun on January 11th.
Mars (magnitude +0.8, in Virgo) rises around midnight. It's highest in the south before the first light of dawn. Mars is 3/4° from Gamma Virginis, 2 magnitudes fainter, on the mornings of December 28, 29, and 30. By January 4th it moves nearly 3° away from the star.
In a telescope Mars is gibbous and still small, not quite 7 arcseconds in diameter.
Jupiter (magnitude –2.7, in central Gemini) is nearly at its January 5th opposition. So it glares low in the east as twilight fades, then rises higher in the east all evening (with Pollux and Castor to its left and fainter Gamma Geminorum a similar distance to its right). It blazes highest in the middle of the night.
In a telescope Jupiter is 47 arcseconds wide, as big as you're going to see it. Read up on observing Jupiter in the January Sky & Telescope.
Saturn (magnitude +0.6, in Libra) is well up the southeast as dawn begins to brighten. Look for it far to the lower left of Mars and Spica, and far below brighter Arcturus.
Uranus (magnitude 5.8, in Pisces) is high in the south right after dark.
Neptune (magnitude 7.9, in Aquarius) is getting low in the southwest 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) is Universal Time (UT, UTC, or GMT) minus 5 hours.
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