This Week’s Sky at a Glance, January 16 – 24

Some daily sky sights among the ever-changing Moon, planets, and stars.

Comet Lovejoy imaged on December 30th by Alan Tough in Australia.

Comet Lovejoy as imaged on December 30th by Alan Tough using a 4-inch f/5 refractor.

Comet Lovejoy is still at its predicted brightest this week, and it's high in the evening sky with no Moon yet. The comet is glowing at about 4th magnitude more or less west of the Pleiades. It's very obvious in binoculars, and it's dimly visible to the unaided eye if you have a very good dark sky. Article and finder chart: See Comet Lovejoy Tonight.

Friday, January 16

Venus and Mercury in twilight Jan. 17, 2015

Early this week, Mercury is still fairly easy to pick up as it moves away to the right of Venus.

Crescent Moon with Venus, Mercury, and Mars on Jan 21 - 23, 2015

Mercury has dropped away and faded greatly by the time the waxing crescent Moon enters the twilight scene. (The Moon, shown three times actual size, is plotted for a viewer near the middle of North America. The visibility of faint objects in bright twilight, such as Mercury, is exaggerated.)

Bright Capella high overhead, and bright Rigel in Orion's foot, are at almost the same right ascension — so they cross your sky’s meridian at almost the same time (around 9:30 p.m., depending on how far east or west you live in your time zone). So whenever Capella passes its very highest, Rigel marks true south over your landscape. Both shine brilliantly at zero magnitude.

(Capella goes exactly through your zenith if you're at latitude 46° north: for instance Portland, Oregon; Montreal; central France; Tokyo.)

Saturday, January 17

Comet Lovejoy is 8° west-southwest of the Pleiades this evening and tomorrow evening. Finder charts and photos.

Sirius twinkles brightly after dinnertime below Orion this week. Around 8 or 9 p.m., depending on your date and location, Sirius shines precisely below fiery Betelgeuse in Orion's shoulder. How accurately can you time this event for your site, perhaps using a plumb bob or the edge of a building? Sirius leads Betelgeuse early in the evening; Betelgeuse leads later. Welcome to pre-telescopic astronomy.

Sunday, January 18

Orion shines high in the southeast in early evening now. Orion is the showiest constellation, but his main pattern is surprisingly small compared to some of his dimmer neighbors. The biggest of these is Eridanus the River, enormous but hard to trace. Dimmer Fornax the Furnace, to Eridanus's lower right, is almost as big as Orion. Even the main pattern of Lepus, the Hare cowering under Orion's feet, isn't much smaller than Orion's main pattern.

Monday, January 19

The Bear is already coming out of hibernation. In the north-northeast these evenings, Ursa Major is walking upwards from the horizon nose first. His brightest part is the Big Dipper, with its bowl to the upper right and its handle dragging.

Tuesday, January 20

Gemini shines high in the east these evenings, off to the left of Orion. In Gemini's center lies R Geminorum, a red long-period variable star sporting the rare elements zirconium and technetium. R Gem is brightening toward a February maximum. As of January 14th it was already magnitude 7.0, ahead of schedule. See the article, photo, and finder chart in the January Sky & Telescope, page 51.

New Moon (exact at 8:14 a.m. Eastern Standard Time).

Wednesday, January 21

Look low in the west shortly after sunset for the thin crescent Moon forming a triangle with Venus and fainter Mercury, as shown above (for North America). Bring binoculars.

Thursday, January 22

The waxing crescent Moon now shines well above Venus and to the right of Mars, as shown above.

Mutual event among Jupiter's moons. Early on Friday morning, from 4:06 to 4:20 a.m. EST, Callisto casts its shadow onto its neighbor moon Ganymede, dimming Ganymede by an obvious 1.4 magnitudes around the middle of that time. Ganymede is normally the brightest of Jupiter's four big moons. Even with just a small telescope, you can watch it briefly become a trace fainter than Callisto, which normally is the faintest. Ganymede, Callisto, and Europa will all appear close together.

Friday, January 23

The Moon, dim Mars, and bright Venus form a big diagonal line in the west in twilight, as shown above. And can you still detect Mercury? It's been fading fast day by day.

Three shadows on Jupiter. Late tonight Callisto, Io, and Europa are all casting their tiny black shadows onto Jupiter at once, from 1:27 to 1:52 a.m. Saturday morning EST (10:27 to 10:52 p.m. Friday evening PST). Then all three satellites themselves appear in front of Jupiter at once (and hence are practically invisible) from 2:08 to 2:12 a.m. EST.

Griffith Observatory in Los Angeles will livestream the event from 8:30 to 11:00 p.m. PST (11:30 p.m. to 2 a.m. EST, or 4:30 to 7:00 January 24 UT).

Saturday, January 24

Every week, brilliant Sirius, the Dog Star, glitters higher in the southeast after dinnertime. Look high above it for Betelgeuse in Orion's shoulder, shining reddish-orange. To their left is Procyon, the Little Dog Star, forming the equilateral Winter Triangle with them. Sirius, Betelgeuse, and Procyon are 8.6, 500, and 11.5 light-years away, respectively. Here's some starwatching you can do through even the worst city light pollution.

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).

Pocket Sky Atlas

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but it's still less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae.

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 fairly heavy and expensive). 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 coming off its close pairing with Venus. Look for them in low the southwest in the afterglow of sunset. Venus is by far the most obvious, shining at magnitude –3.9. On Friday the 16th Mercury is still just 2.2° to Venus's lower right, and still magnitude –0.5. But Mercury fades rapidly day by day, while falling away farther to the lower right. By week's end it's essentially gone.

Mars (magnitude +1.2, in Aquarius) continues to glow in the southwest at dusk, to Venus's upper left. It still sets around 8 p.m.

Jupiter on Dec. 27, 2014

Jupiter's Great Red Spot had just come around into view when S&T's Sean Walker took this image at 5:48 December 27th UT, using a 12.5-inch reflector. South is upper left. On the central meridian in the south is dark-rimmed Oval BA, called Red Spot Junior, "paler than in previous years" he notes. The northern side of the bright Equatorial Zone sports prominent bluish festoons.

Jupiter (magnitude –2.5, in western Leo) rises around 6 or 7 p.m in the east-northeast. Nearly an hour later, fainter Regulus (magnitude +1.4) rises below it. By 9 p.m. They're shining high in the east.

Saturn (magnitude +0.5, at the head of Scorpius) glows in the southeast before and during dawn. Look about 1.3° below it, a little-finger-width at arm's length, for Beta Scorpii, magnitude 2.5, a showpiece double star for telescopes. Below them by 10°, look for orange Antares.

Uranus (magnitude 5.8, in Pisces) is still in the southwest right after dusk.

Neptune (magnitude 7.9, in Aquarius) is sinking down into the evening twilight, in the background of Mars.


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.

“This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours.”

— Neil deGrasse Tyson, 2014.

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