This Week’s Sky at a Glance, December 27 – January 4


Moon and Venus, Dec. 27, 28, 29, 2019

This week the Moon returns to the evening sky as a crescent, then waxes to first quarter. On Friday the 27th it's elusively low in twilight with faint, even-lower Saturn; bring binoculars.

Venus in Capricornus, Jan. 3, 2019

A week later, Venus is higher and Alpha and Beta Cap are sinking away.

Friday, Dec. 27

• In twilight about 30 minutes after sunset, spot the thin crescent Moon low in the southwest. It's well to the lower right of Venus, as shown here. Using binoculars, look for faint Saturn disappearing toward the horizon a few degrees to the Moon's lower right. This is the last you'll probably see of Saturn in the evening sky until next summer.

• As the stars come out, face north and look high. Cassiopeia is now a flattened M canted at about a 45° angle (depending on where you live). Hardly more than an hour later, the M has turned horizontal! Constellations passing near the zenith appear to rotate rapidly with respect to the direction "up."

• Algol, the prototype eclipsing binary star, is at its minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 8:51 p.m. EST tonight. It takes several more hours to rebrighten.

• Know someone who got a telescope? Maybe you? To get them started right, point 'em here: What to See with Your New Telescope, starting with how to set it up, figure it out, and make it work.

Saturday, Dec. 28

• The crescent Moon now pairs fabulously with Venus in twilight, as shown above. They'll be only a couple of degrees apart at dusk for the Americas. Think photo opportunity! These are the two brightest celestial objects after the Sun.

Now from the bright to the subtle: As night deepens, look to their right (by about 9°) for Alpha and Beta Capricorni coming into view. Both are double stars for binoculars. Alpha is the easier one.

Sunday, Dec. 29

• Sirius, the Dog Star, sparkles low in the east-southeast after dinnertime. Procyon, the Little Dog Star, shines to Sirius's left, by about two fist-widths at arm's length. 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.

• And whenever Sirius, the "Winter Star," twinkles low in the southeast, Vega, the "Summer Star," twinkles low in the northwest. If you live near 40° north latitude they're equally low (7°) around 8 p.m. now, depending on where you live in your time zone.

Mars and Antares at dawn, Dec. 31, 2019

As Mars gets higher, Antares emerges from below to join it. They'll pass a wide 5° from each other at their conjunction on January 18th.

Mars and Antares at dawn, Jan. 4, 2020.

Getting closer. . . . Mars, at magnitude +1.6, is hardly any brighter than Delta Scorpii below it (about magnitude 1.8, slightly variable) and Beta Sco (2.6).

Monday, Dec. 30

• The Moon at dusk forms a wide, more-or-less level triangle with Venus to its lower right and Fomalhaut to its lower left.

Tuesday, Dec. 31

• Now, at dusk, the Moon forms a rough right triangle with Fomalhaut below it and Venus farther to Fomalhaut's right.

• After the noise and whoopla when we enter the 2020s at midnight, step outside into the silent, cold dark. The Moon will have set. Shining high in the south will be Sirius, with the other bright 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 now stands upright, just about in balance.

Wednesday, Jan. 1

• The Winter Hexagon is the biggest and brightest asterism in the sky — at least the biggest one that's commonly recognized. After about 8 p.m., start with bright Sirius low in the southeast. Look left of it by two or three fists at arm's length to find Procyon. From there go upper left to the Pollux and Castor pair, then high up to bright Capella (hitting Menkalinan before getting there). Then jog right to orange Aldebaran, lower right to Rigel in Orion's leading foot, and back down lower left to Sirius.

Inside the Hexagon, well off center, shines fire-colored Betelgeuse.

Thursday, Jan. 2

• First-quarter Moon (exact at 11:45 p.m. tonight EST). The Moon, in Cetus, is lower left of the Great Square of Pegasus at dusk, then directly left of it by 7 or 8 p.m.

• The Great Square is part of the enormous Andromeda-Pegasus complex, which now runs from near the zenith far down toward the western horizon.

Near the zenith, spot Andromeda's high foot: 2nd-magnitude Gamma Andromedae (Almach), slightly orange. Andromeda is standing on her head, the star that forms the Great Square's top corner. The square is balancing on its opposite corner. Down from there run the stars outlining Pegasus's neck and head, ending at his nose: 2nd-magnitude Enif, due west and also slightly orange.

Friday, Jan. 3

• This year the brief Quadrantid meteor shower is — at last! — well timed for North America, especially the East. Tonight Earth is predicted to pass through the densest part of the Quadrantid meteoroid stream for roughly six hours centered around 3 a.m. Saturday morning January 4th Eastern Standard Time, right in the favorable early-morning meteor-watching hours for the East. Wherever you are, the first-quarter Moon sets around 1 or 2 a.m. local time. Under ideal dark conditions with the radiant overhead you might see up to 120 meteors per hour. Off peak, your count may be more like a dozen or two per hour at best.

Bundle up warmly in many layers! This is the coldest time of night at the coldest time of year, and if the sky is clear which it will be if you're meteor-watching, you've got radiational cooling to boot. And you'll be sitting or lying still as you gaze into the stars overhead. But as every astronomer knows, there is no too cold, there is only underdressed. I sometimes bundle a 50-watt hotpad inside my clothes, connected to the house by a long extension cord. Put it against your belly, and blood circulation will carry some of the warmth to your toes and fingertips.

The shower's radiant is in northern Bootes. See Bob King's article in the January Sky & Telescope, page 48.

Saturday, Jan. 4

• Look above the Moon after dark for the two, or possibly three, brightest stars of Aries.

• Earth is at perihelion, its closest to the Sun for the year, at 2:48 a.m. on the morning of January 5th EST. This week we're 3.3 percent closer to the Sun than at aphelion in July.

• Purely by coincidence, January 5th also has the latest sunrise of the year if you're near 40° north latitude.


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, cold or not. 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.

Jumbo Pocket Sky Atlas cover

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and hundreds of telescopic galaxies, star clusters, and nebulae among them. Shown above is the Jumbo Edition for easier reading in the night. Sample chart.

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) and 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). 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."

This Week's Planet Roundup

Mercury is hidden deep in the glare of the Sun.

Venus (magnitude –4.0, crossing central Capricornus) shines in the southwest in evening twilight, higher each week. It's coming into a grand "Evening Star" apparition that will continue all winter and into the spring. In a telescope Venus still appears small (13 arcseconds) and gibbous, since it's still nearly on the far side of the Sun from us.

Mars (magnitude +1.6, in Libra) is fairly low in the southeast before and during early dawn. It too is still on the far side of the Sun from us and so is a very tiny 4 arcseconds in diameter.

Far and small as Mars may be, it's on its way to a fine opposition next October, when it will attain an especially large apparent diameter of 22 arcseconds and shine at an impressive magnitude –2.6, 50 times brighter than now.

Jupiter is hidden in conjunction with the Sun.

Saturn (magnitude +0.6) is sinking away deep into the sunset, ever farther to the lower right of Venus — which outshines it by 60 times. Friday the 27th may be your last day to see it, when it's 19° lower right of Venus and 5° or 6° lower right of the Moon for North America, as shown at the top of this page. Binoculars help.

Uranus (magnitude 5.7, in southern Aries) and Neptune (magnitude 7.9, in eastern Aquarius) stand high in the south-southeast and lower in the southwest, respectively, right after dark. Use our 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, GMT, or Z time) minus 5 hours.

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.

2 thoughts on “This Week’s Sky at a Glance, December 27 – January 4

  1. James

    Hmm, purely by coincidence? Part of the offset in the sunrise times is due to the tilt of the earth, and part is due to the elliptical orbit? So a variation in the sunrise at perihelion is to be expected?

    Since the earth is moving faster, it covers a greater arc, and a solar day is longer, which changes noon and the sunrise and sunset times…

    I could be totally wrong, of course. I’m very much an amateur.

    Great post!

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