This Week’s Sky at a Glance, January 23 – 31

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

Comet Lovejoy is now fading somewhat, and the Moon increasingly brightens the night sky this week for comet viewers. Even so, the comet is still a nice sight in binoculars at magnitude 4½ or so. And it's high overhead. See our article and finder chart: Where To See Comet Lovejoy Tonight.

Friday, January 23

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

The waxing crescent Moon on the 23rd guides the way down to twilight planets.

The Moon, dim Mars, and bright Venus form a big diagonal line in the west in twilight, as shown here. And can you still detect tiny, faint Mercury? Bring binoculars.

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 triple-shadow 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

Brilliant Sirius, the Dog Star, glitters 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. It forms 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.

Sunday, January 25

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 26

Earth to dodge a bullet! A relatively large near-Earth asteroid, 2004 BL86, is flying by our planet, passing us by three times the distance of the Moon. Tonight the asteroid will brighten to 9th magnitude as it crosses Cancer, nicely placed in the evening hours for telescope users in the Americas. See the article and detailed finder chart in the February Sky & Telescope, page 50, or our version online: Mountain-size Asteroid Glides Past Earth.

Tuesday, January 27

"If I had to choose just one deep-sky object to demonstrate the appeal of binocular astronomy, it would probably be the Pleiades," writes Gary Seronik. The Pleiades are certainly a nice sight overall. But the cluster also holds a secret in its center: the 8th-magnitude double star South 437, barely resolvable with 10× glasses. See Gary's column and chart in the February Sky & Telescope, page 45. The large black circle on his chart spans a 10× binocular's 5° field of view.

Algol shines at its minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours tonight centered on 10:42 p.m. EST.

The waxing Moon crossing the evening sky, Jan. 27-31, 2015

Watch the waxing gibbous Moon walk eastward across the evening constellations this week.

Wednesday, January 28

Look for the Pleiades over the Moon at nightfall, as shown above. The scene rotates clockwise as the evening advances.

Thursday, January 29

The Moon shines near Aldebaran and the Hyades at dusk, as shown above.

Friday, January 30

The waxing gibbous Moon shines above Orion this evening. It's near Zeta Tauri, the fainter of the two stars that mark the tips of Taurus's long horns.

Algol is at minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 7:31 p.m. EST.

Saturday, January 31

With a small telescope, you can watch Jupiter's inner moon Io fade away into eclipse by Jupiter's shadow around 10:45 p.m. EST (7:45 p.m. PST). Io will be just barely off Jupiter's western limb when the eclipse happens. That's because we're only 6 days from Jupiter's opposition.

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 disappears deep into the glow of sunset.

Venus (magnitude –3.9) shines in the west-southwest during evening twilight. It's getting a little higher each week, on its way into a grand apparition as the high "Evening Star" this spring.

Mars (magnitude +1.2, in Aquarius) still glows in the southwest at dusk, to the upper left of bright Venus. It continues to set around 8 p.m.

Jupiter (magnitude –2.6, in western Leo) comes to opposition next week, so it's big and bright. It rises in the east-northeast in twilight, and by 9 p.m. it's shining good and high in the east, with fainter Regulus (magnitude +1.4) down below it. Jupiter and Regulus pass highest in the south around the middle of the night.

Saturn (magnitude +0.5, at the head of Scorpius) is well up in the southeast before and during dawn. Look 1° below it for Beta Scorpii, magnitude 2.5, a showpiece double star for telescopes. Below them by 9° is orange Antares.

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

Neptune (magnitude 7.9, in Aquarius) is sinking away into the evening twilight.


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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