This Week’s Sky at a Glance, January 31 – February 9 – Sky & Telescope

FRIDAY, JANUARY 31

■ The waxing crescent Moon shines under Saturn this evening, as shown below. Venus, more than 200 times brighter than Saturn, watches from above. (Saturn is magnitude +1.1, Venus is –4.8.)

SATURDAY, FEBRUARY 1

■ Now it’s Venus’s turn to host the lunar visitor, as shown above. They are not as paired as they look. Venus, currently 4 light-minutes away, is about 200 times farther from us than the Moon’s current distance of 1.2 light-seconds.

■ Jupiter’s moon Io enters onto Jupiter’s face at 6:41 p.m. EST coming from the east, then it exits from Jupiter’s western limb at 8:53 p.m. EST. Following behind Io across the planet’s face, from 7:50 to 10:02 p.m. EST, will be Io’s tiny black dot of a shadow.

SUNDAY, FEBRUARY 2

■ Today is the center of winter. We cross the midpoint between the December solstice and the March equinox at 6:50 p.m. EST (23:50 UT). That minute is the very bottom of the wheel of the year, astronomically speaking.

In ancient Gaelic cultures this day was Imbolc: one of the four traditional “cross-quarter” days between the solstices and the equinoxes. The others were May Eve, Lammas, and Halloween, although since those times our calendar has shifted these dates a bit from the cross-quarter points.

Groundhog Day (like its German weather-predicting predecessor, Badger Day) was originally the cross-quarter day. But now Groundhog Day is considered to be fixed as February 2nd, thus avoiding the need for yearly adjustments.

■ On Groundhog Day evening look due east, not very high, for twinkly Regulus. Extending upper left from it is the Sickle of Leo, a backward question mark leaning leftward. It’s about a fist and a half long. “Leo announces spring,” goes an old saying. Actually, Leo showing up in the evening announces the cold, sloppy back half of winter. Come spring, Leo will already be high.

MONDAY, FEBRUARY 3

■ The biggest well-known asterism (informal star pattern) is the Winter Hexagon. It fills the sky toward the east and south these evenings.

Start with brilliant Sirius at its bottom. Going clockwise from there, march up through Procyon, Pollux and Castor, Menkalinan and Capella on high, down to Aldebaran, then to Rigel in Orion’s foot, and back to Sirius. Betelgeuse shines inside the Hexagon, way off center.

The Hexagon is somewhat distended. But if you draw a line through its middle from Capella down to Sirius, the “Hexagon” is fairly symmetric with respect to that long axis.

Take the line from Aldebaran to Capella, turn it to go from Aldebaran to Betelgeuse instead, and the Winter Hexagon becomes the Heavenly G.

TUESDAY, FEBRUARY 4

■ First-quarter Moon (exact at 3:02 a.m. EST tonight, after it sets for most of North America). At dusk the Moon shines high in the southwest, in Aries. After dark look for the two brightest stars of Aries less than a fist at arm’s length to the Moon’s right. These are Alpha and Beta Arietis, Hamal and Sheratan, magnitudes 2.0 and 2.6. Cover the Moon with your hand to reduce its glare.

Just a finger-width below Beta, can you make out Gamma Arietis (Mesarthim), mag 3.9? It’s a fine double star waiting right there when you have your telescope out for the Moon tonight. Both components are magnitude 4.6 and white. They’re lined up almost precisely north-south 7.4 arcseconds apart.

The pair is 165 light years away, and each star is 40 times as luminous as the Sun. They’re at least 370 a.u. apart, which is at least 12 times Neptune’s separation from the Sun. So each of them could have a planetary system undisturbed by the other. But they are very young: only about 34 million years old.

■ Jupiter reaches its stationary point (the end of its retrograde loop) and resumes its prograde (eastward) motion against the stars.

WEDNESDAY, FEBRUARY 5

■ The Moon occults the Pleiades late tonight for the western U.S. and Canada. The dark limb of the 60% sunlit waxing gibbous Moon will snap up different stars at different times depending on your location. You could just watch. . . or plan ahead:

The brightest of the Pleiades is Alcyone (Eta Tauri), magnitude 2.9. Map and timetables for its occultation. Instructions: The first two tables there, with predictions for many cities, are long. The first table gives the times of the star’s disappearance behind the Moon’s dark limb; the second gives its reappearance out from behind the Moon’s bright limb, which will be much less observable. Scroll to be sure you’re using the correct table; watch for the new heading as you scroll down. The first two letters in each entry are the country abbreviation; CA is Canada, not California. The times are in UT (GMT) February 6th. UT is 5 hours ahead of Eastern Standard Time, 6 hours ahead of CST, 7 ahead of MST, and 8 ahead of PST.

For instance: at Denver, Alcyone will disappear at 1:22 a.m. MST Thursday morning the 6th, when you’ll find the Moon just 8° above the west-northwest horizon (azimuth 295°).

Maps and timetables for three other bright Pleiades stars are here.

THURSDAY, FEBRUARY 6

■ Sirius the Dog Star blazes in the southeast after dinnertime, the brightest star of Canis Major. In a dark sky where lots of stars are visible, the constellation’s points can be connected to form a convincing dog seen in profile. He’s currently standing on his hind legs, facing right. Sirius shines on his chest like a dogtag, to the right or lower right of his faint triangular head.

But through the light pollution where most of us live, only his five brightest stars are easily visible. These form the Meat Cleaver. Sirius is the cleaver’s top back corner, its blade faces right, and its short handle is down below pointing lower left.

FRIDAY, FEBRUARY 7

■ Orion is now high in the southeast right after dark. Left of it is Gemini, headed up by Castor and Pollux at far left. The stick-figure Twins are still lying on their sides.

Well below their legs is bright Procyon. Standing 4° above Procyon is 3rd-magnitude Gomeisa, Beta Canis Minoris, the only other easy naked-eye star of Canis Minor. The Little Dog is seen in profile, but only his back and the top of his head. Procyon marks his rump, Beta CMi is the back of his neck, and two fainter stars just above that are the top of his head and his nose. Those last two are only 4th and 5th magnitude, respectively. Binoculars help through light pollution.

SATURDAY, FEBRUARY 8

■ The bright gibbous Moon shines over Mars, Pollux, and Castor at nightfall, as shown below. As evening grows late this scene rotates clockwise, so that by 10 or 11 p.m. Mars shines straight left of the Moon.

■ Have you ever closely compared the colors of Betelgeuse and Aldebaran? Can you detect any difference in their colors at all? I can’t, really. Yet Aldebaran, spectral type K5 III, is often called an “orange” giant, while Betelgeuse, spectral type M1-M2 Ia, is usually called a “red” supergiant. Their temperatures are indeed a bit different: 3,900 Kelvin and 3,600 Kelvin, respectively.

A complication: Betelgeuse is brighter, and to the human eye, the colors of bright objects appear, falsely, to be desaturated: looking paler (whiter) than they really are. You can get a slightly better read on the colors of bright stars by defocusing them a bit, to spread their light over a larger area of your retina.

■ Jupiter’s innermost large moon, Io, crosses the planet’s bright face from 8:33 to 10:44 p.m. EST, distantly followed by its tiny black shadow (more readily detectable) from 9:46 to 11:58 p.m. EST. Both Moon and shadow creep from celestial east to west with respect to Jupiter. Callisto shines nearby in the foreground.

SUNDAY, FEBRUARY 9

■ Tonight the bright Moon shines amid Mars, Pollux, and Castor. The scene above shows them the way they’re oriented at nightfall.

■ With a telescope, watch just a little east of Jupiter’s limb for Europa to emerge from eclipse out of Jupiter’s shadow at 6:36 p.m. EST, if the sky is dark by then at your longitude. The farther east you live the better.

After that, anyone across North America can watch for Io also to emerge from eclipse at 9:16 p.m. EST.

This Week’s Planet Roundup

Mercury is out of sight in superior conjunction with the Sun.

Venus (magnitude –4.8, near the dim Circlet of Pisces) shines high and bright as the “Evening Star” in the southwest during twilight, then lower in the west-southwest as evening grows late. Two hours after complete dark, it sets due west.

In a telescope this week Venus appears about 35% sunlit: a thick crescent. Venus is enlarging week by week as it swings toward us — it’s now about 34 arcseconds from pole to pole — while waning in phase as it draws closer to our line of sight to the Sun. It’ll be 55 arcseconds in diameter when it becomes a thin crescent and plunges down into the sunset when winter nears its end.

Mars, two weeks past opposition, is noticeably fading and shrinking: to about magnitude –0.9 and 13 arcseconds in diameter. Mars comes into view in twilight as a steady orange spark in the east. As darkness deepens, watch for Pollux and Castor emerge into view left of it.

For telescopes, Mars climbs higher into best atmospheric seeing as evening advances. It passes just south of the zenith around 10 or 11 p.m. A map of its major surface features is in the January Sky & Telescope, page 48, in Bob King’s article “Mars is in Fine Form.” See also Bob’s Mars Extravaganza online with a surface-feature map. To find which side of Mars (i.e. which part of the map) will be facing you at the date and time you’ll observe, use our Mars Profiler tool.

Jupiter, two months past opposition, shines at a bright magnitude –2.5 in Taurus. It dominates the high south after dusk, near Aldebaran and the Pleiades. Jupiter is about 42 arcseconds wide.

Saturn, magnitude +1.1 in Aquarius, is a little spark lower and lower below Venus during and just after dark. The gap between them is widening. Saturn is 11° below Venus on Friday January 31st and 15° below it by February 7th.

Uranus, magnitude 5.7 at the Taurus-Aries border, is very high toward the southwest during early evening, 18° west of Jupiter along the ecliptic. You’ll need a good finder chart to tell it from the similar-looking surrounding stars. See last November’s Sky & Telescope, page 49.

Neptune, tougher at magnitude 7.9, is between Venus and Saturn right after dark. Again you’ll need a sufficient finder chart.

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 and graphics that also depend on longitude (mainly Moon positions) are for North America.

Eastern Standard Time (EST) is Universal Time minus 5 hours. UT is also known as UTC, GMT, or Z time.

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 a more detailed constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential magazine of astronomy.

Once you get a telescope, to put it to good use you’ll need a much more detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas, in either the original or Jumbo Edition. Both show all 30,000 stars to magnitude 7.6, and 1,500 deep-sky targets — star clusters, nebulae, and galaxies — to search out among them.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many, as well as many more deep-sky objects. It’s currently out of print, but maybe you can find one used.

The next up, once you know your way around well, are the even larger Interstellarum atlas (201,000+ stars to magnitude 9.5, and 14,000 deep-sky objects selected to be detectable by eye in large amateur telescopes), andUranometria 2000.0 (332,000 stars to mag 9.75, and 10,300 deep-sky objects). And read How to Use a Star Chart with a Telescope. It applies just as much to charts on your phone or tablet as to charts on paper.

You’ll also want a good deep-sky guidebook. A beloved old classic is the three-volume Burnham’s Celestial Handbook. An impressive more modern one is the big Night Sky Observer’s Guide set (2+ volumes) by Kepple and Sanner. The pinnacle for total astro-geeks is the new Annals of the Deep Sky series, currently at 11 volumes as it works its way forward through the constellations alphabetically. So far it’s up to H.

Can computerized telescopes replace charts? Not for beginners I don’t think, and not for scopes on mounts and tripods that are less than top-quality mechanically. Unless, that is, you prefer spending your time getting finicky technology to work rather than learning how to explore the sky. 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 and a curious mind.” Without these, “the sky never becomes a friendly place.”

If you do get a computerized scope, make sure that its drives can be disengaged so you can swing it around and point it readily by hand when you want to, rather than only slowly by the electric motors (which eat batteries).

However, finding faint telescopic objects the old-fashioned way with charts isn’t simple either. Do learn the essential tricks at How to Use a Star Chart with a Telescope.

Audio sky tour. Out under the evening sky with your
earbuds in place, listen to Kelly Beatty’s monthly
podcast tour of the naked-eye heavens above. It’s free.

“The dangers of not thinking clearly are much greater now than ever before. It’s not that there’s something new in our way of thinking, it’s that credulous and confused thinking can be much more lethal in ways it was never before.”
            — Carl Sagan, 1996

“Facts are stubborn things.”
             John Adams, 1770