Moon, Venus, Mars, Jan. 30-31, 2017
The waxing crescent Moon joins Venus and Mars at January's end. The 10° scale bar is about a fist-width at arm's length. (These maps are always plotted exact for an observer near the middle of North America, at latitude 40° N, longitude 90° W. The Moon is always shown three times its actual apparent size.)
Saturn and Antares at dawn, early Feb. 2017
All week, Saturn and Antares await you in the south-southeast in early dawn.

Friday, January 27

• The sky's biggest asterism (informal star pattern) — at least the biggest widely recognized — is the Winter Hexagon. It now fills the sky toward the east and south after dinnertime. Start with brilliant Sirius at its bottom. Going clockwise from there, march through Procyon, Pollux and Castor, Menkalinan and Capella very high, Aldebaran over to Capella's lower right, down to Rigel in Orion's foot, and back to Sirius.

Betelgeuse shines inside the Hexagon, off center.

• New Moon (exact at 7:07 p.m. EST).

Saturday, January 28

• After dark the Great Square of Pegasus is sinking down in the west. It's to the right or upper right of Venus and Mars, tipped onto one corner. Meanwhile the Big Dipper is creeping up in the north-northeast, tipped up on its handle.

Sunday, January 29

• Below Orion's feet crouches surprisingly large Lepus, the Hare. Explore the telescopic deep-sky sights around his ears (just below Rigel) using Sue French's Deep-Sky Wonders article and map in the February Sky & Telescope, page 54.

• The deep, flat-bottomed eclipsing binary star RW Tauri plummets from 8th to 12th magnitude and back tonight, centered on 1:10 a.m. EST (10:10 p.m. PST). See the observing project in the January Sky & Telescope, page 48.

Monday, January 30

• The thin Moon hangs under Venus early this evening, as shown above. Compare their phases; Venus in a telescope is a much thicker crescent than this evening's Moon.

• Algol, the prototype eclipsing binary star, should be at minimum brightness (magnitude 3.4 instead of its usual 2.4) for about two hours centered on 11:04 p.m. EST (8:04 p.m. PST). Algol takes several hours before and after to fade and rebrighten. Info and comparison star chart.

Tuesday, January 31

• The waxing crescent Moon, bright Venus, and faint, distant Mars form a triangle in the west during and after dusk, as shown above.

Wednesday, February 1

• As soon as it's dark, spot the equilateral Winter Triangle in the southeast. Sirius is the triangle's brightest and lowest star. Betelgeuse stands above Sirius by about two fists at arm's length. Left of their midpoint is Procyon.

And, standing directly above Procyon now (depending on your latitude) is Gomeisa, Beta Canis Minoris, the only other easy naked-eye star of Canis Minor.

Thursday, February 2

• Right after dark this week, face east and look almost overhead. The bright star there is Capella, the Goat Star. To the right of it, by a couple of finger-widths at arm's length, is a small, narrow triangle of 3rd and 4th magnitude stars known as "the Kids." Although they're not exactly eye-grabbing, they form a never-forgotten asterism with Capella.

• Algol should be at minimum light for about two hours centered on 7:54 p.m. EST.

Friday, February 3

• First-quarter Moon (exact at 11:19 p.m. EST). At sunset the half-lit Moon is high in the south, and after dark it balances on the dim head of Cetus. Spot the stars of Aries to its upper right, and the Pleiades a little farther to its upper left.

Saturday, February 4

• In early evening the Pleiades stand above the Moon, and Aldebaran shines left of the Moon.


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.

Pocket Sky Atlas, jumbo edition
The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but it's less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae. Shown above is the new Jumbo Edition for easier reading in the night. Click image for larger view.

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 new 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, is 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, 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 (still magnitude –0.2) is sinking very low in the glow of dawn. Use binoculars to try for it 30 or 40 minutes before sunrise, just above the east-southeast horizon. Mercury is far lower left of Saturn: 22° from Saturn on the morning of January 28th, and 31° from it by the morning of February 4th.

Venus is that dazzling white UFO of a thing high in the southwest during twilight and long after. It's currently magnitude –4.7 or –4.8, entering its time of peak brightness. Just to its upper left is tiny orange Mars, now only 0.5% as bright.

In a telescope Venus is slightly less than half sunlit. It's growing larger as it approaches us and is now about 30 arcseconds from cusp to cusp. For the rest of the winter, Venus will continue to enlarge as its phase wanes down to a thin crescent.

Venus in a telescope is least glary when viewed in bright twilight. So get your scope on it as soon as you can see it naked-eye, perhaps before sunset.

Mars (magnitude +1.1) is the faint "star" upper left of Venus. They're 5½° apart this week, their minimum separation for this year; Venus will soon start to move back down and away. In a telescope Mars is just a tiny fuzzblob 5 arcseconds wide.

Vesta, the brightest asteroid, is still a very accessible magnitude 6.5 in Gemini near Pollux and Castor. Article and finder chart.

Jupiter with Red Spot on Jan. 24, 2017
Jupiter on January 24th, imaged by Christopher Go. South is up. Upper left of the Great Red Spot is small, pale-orange Oval BA. The separation between them has increased in recent weeks. In the northern hemisphere, tiny white outbreaks have appeared in the North Equatorial Belt at about the same longitude as the Red Spot. Will they grow?

Jupiter (magnitude –2.2, in Virgo) rises around 11 p.m. and shines brightly high in the south in the hours before dawn. Spica dangles 3½° below or lower right of it. Jupiter is creamy white. Spica is an icier shade of white with a trace of blue (once it's fairly high).

In a telescope Jupiter is 39 arcseconds across its equator, on its way to 44 arcseconds in late March and April. (Opposition is April 7th.)

Saturn (magnitude +0.5, in southern Ophiuchus) is in the southeast before and during dawn. Redder Antares, magnitude +1.0, twinkles 15° to Saturn's right.

Uranus (magnitude 5.8, in Pisces) is still high in the southwest right after dark. Finder chart.

Neptune (magnitude 8.0, in Aquarius) sets shortly after the end of 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

"Objective reality exists. Facts are often determinable. Science and reason are no political conspiracy; they are how we discover objective reality. Civilization's survival depends on our ability, and willingness, to do this."
— Alan MacRobert, your Sky at a Glance editor

"Facts are stubborn things."
— John Adams, 1770

March For Science on April 22nd, to “champion publicly funded and publicly communicated science as a pillar of human freedom and prosperity.”



Image of Anthony Barreiro

Anthony Barreiro

January 27, 2017 at 4:51 pm

Alan, I wholeheartedly support your editorial comment. Thank you.

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January 27, 2017 at 5:04 pm

You got that right about Mars being a tiny fuzzblob. I looked at Venus at 144x through my 130mm reflector, and it was impressive. Then I pointed it at Mars, big disappointment. I guess I'll have to wait until 2018 to get a good look at Mars.

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