This Week's Sky at a Glance, February 4 – 12

FRIDAY, FEBRUARY 4

■ The Great Square of Pegasus stands on one corner in the western sky right after dark, diamond style. Its upper left side points lower left to the crescent Moon — by just a little more than its own length.

■ Have you ever closely compared the colors of Betelgeuse and Aldebaran? Can you detect any difference in their colors at all? I don't think I can. 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 slightly different: 3,900 Kelvin and 3,600 Kelvin, respectively, a temperature difference of 8%.

A complication: Betelgeuse is brighter. And to the human eye, the colors of bright objects appear, falsely, to be desaturated: 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.

■ The solar system has four terrestrial (rocky) planets: Mercury, Venus, Earth, and Mars. All four are visible at dawn this week, as shown below.

SATURDAY, FEBRUARY 5

■ After it’s good and dark look due east, not very high, for twinkly Regulus. Extending upper left from it is the Sickle of Leo, a backward question mark. "Leo announces spring," goes an old saying. Actually, Leo starting to show up in the evening announces the cold, messy back half of winter. Come spring, Leo will already be high.

SUNDAY, FEBRUARY 6

■ The sky's biggest asterism 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, then Menkalinan and Capella high overhead, down to Aldebaran, then to Rigel in Orion's foot, and back to Sirius. Betelgeuse shines inside the Hexagon, off center.

The "Hexagon" is somewhat distended. But if you draw a line through its middle from Capella down to Sirius, it's fairly symmetric around that long axis.

■ Take hold of the line from Aldebaran to Capella, twist it to go from Aldebaran to Betelgeuse instead, and the Winter Hexagon becomes the Heavenly G. It's currently tilting way up. Late in the night, and later in the season, the G turns level as it moves to the southwest.

MONDAY, FEBRUARY 7

■ The Moon, barely half a day short of first quarter (for North America), shines high in the southwest this evening. Look lower left of it by about a fist at arm's length for Menkar (Alpha Ceti), magnitude 2.5.

A little farther to the other side of the Moon is Hamal, Alpha Arietis, magnitude 2.0. Continue on farther in the same direction and you cross dim Triangulum, then you reach the feet stars of Andromeda: first the bright one, then the dimmer one.

■ Sirius the Dog Star blazes in the southeast after dinnertime, the brightest star of Canis Major. In a dark sky with lots of stars in view, the constellation's points can be connected to form a convincing dog profile. He's currently standing on his hind legs. Sirius is on his chest, 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 stubby handle is down below pointing lower left. The handle is Canis Major's tail.

TUESDAY, FEBRUARY 8

■ First-quarter Moon (exact at 8:50 a.m. EST). The first-quarter Moon of February shines very high after dark. When you face it directly soon after nightfall, look for the Pleiades above it and Aldebaran farther to its upper left. Lower left from there, Orion stands upright.

WEDNESDAY, FEBRUARY 9

■ Now the Moon shines more or less between Aldebaran and the Pleiades after dark.

■ Lower left of them stands Orion. Left of Orion is Gemini, headed up by Castor and Pollux at far left. The stick-figure Twins lie on their sides.

■ Well below Gemini's legs is bright Procyon in little Canis Minor: the doglet in partial profile the top of whose head is barely visible in a dark sky (you may have to wait for a moonless night). He's currently vertical. Procyon marks his rump.

THURSDAY, FEBRUARY 10

■ Now, when you face the Moon after dusk, you'll find that it's between Auriga with bright Capella, to the Moon's upper right, and Orion to the Moon's lower left.

FRIDAY, FEBRUARY 11

■ The Moon shines close to the top-to-bottom midline of the Winter Hexagon: the line from Capella to Sirius. See Sunday above.

SATURDAY, FEBRUARY 12

■ The waxing gibbous Moon shines in Gemini this evening. Castor and Pollux are lower left of it early after dark, directly left of the Moon later in the evening, and over it in the early hours of Sunday morning.

■ By 9 p.m. or so, the Big Dipper stands on its handle in the northeast. In the northwest, Cassiopeia also stands on end (its brighter end) at about the same height. Between them is Polaris.

 

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This Week's Planet Roundup

Mercury, Venus, and Mars shine in early dawn. They're low in the southeast, forming a triangle that very gradually changes shape this week as shown above.

Brightest of course is Venus, now peaking at a dazzling magnitude –4.9. In a telescope it's a thick crescent; the globe appears about a quarter sunlit, as always when Venus is at its greatest brilliancy.

Mars is only one three-hundredth that bright, at a paltry magnitude +1.4. Look for it less than a fist to Venus's lower right.

Mercury is about twice that far to Venus's lower left. It brightens from magnitude +0.5 on February 5th to +0.1 on the 12th.

Jupiter (magnitude –2.0, in Aquarius) sinks lower in evening twilight every day. Look west-southwest. It sets around twilight's end.

Saturn is out of sight in conjunction with the Sun.

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

Neptune (magnitude 8.0, in Aquarius) is sinking away in the west-southwest, invisible to the unaided eye some 12° upper left of Jupiter.

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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 (also called UT, UTC, GMT, or Z time) minus 5 hours.

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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 magazine of astronomy.

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) or Uranometria 2000.0 (stars to magnitude 9.75). And be sure to read How to Use a Star Chart with a Telescope. (It applies just as much to charts onscreen 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.

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."

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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.

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"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