This Week's Sky at a Glance, February 12 – 20

FRIDAY, FEBRUARY 12

■ Orion stands his highest in the south by about 8 p.m., looking smaller than you probably remember him appearing early in the winter when he was low. You're seeing the "Moon illusion" effect. Constellations, not just the Moon, seem to look bigger when they're low.

Under Orion's feet, and to the right of Sirius now, hides Lepus the Hare. This is a constellation with a connect-the-dots that really looks like what it's supposed to be. He's a crouching bunny, with his nose pointing lower right, his faint ears extending up toward Rigel (Orion's brighter foot), and his body bunched to the left. His brightest two stars, 3rd-magnitude Alpha and Beta Leporis, form the back and front of his neck.

SATURDAY, FEBRUARY 13

■ 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.

SUNDAY, FEBRUARY 14

■ Have you ever closely compared the colors of Betelgeuse, Aldebaran, and Mars? This winter you have a good chance to do so! Can you detect any difference in their colors at all?

Betelgeuse is the top-left corner of Orion's bright pattern, high in the south in early evening. Aldebaran is two fists at arm's length to the right of Betelgeuse. Mars is now the same distance lower right of Aldebaran.

I can't see any color difference between the two stars. 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 and 3,600 Kelvin, respectively.

Mars, meanwhile, looks to me looks very slightly more yellowish than either star.

A complication: Betelgeuse is brighter than the other two, and to the human eye, the colors of bright objects appear, falsely, to be desaturated: tending 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.

MONDAY, FEBRUARY 15

■ Right after the night is fully dark this week, the W of Cassiopeia shines high in the northwest, standing almost on end. The brightest star between Cassiopeia and the zenith, at that time for the world's mid-northern latitudes, is Alpha Persei (Mirfak). Around and upper left of Mirfak is the Alpha Persei Cluster: a large, very loose swarm of modestly bright stars about the size of your thumbtip at arm's length. They show best in binoculars.

Alpha Per is a true member of the cluster. It and the rest of the group are about 560 light-years away.

TUESDAY, FEBRUARY 16

■ Sirius the Dog Star blazes high in the southeast after dinnertime, the brightest star of Canis Major. Spot it lower left of Orion. In a dark sky with lots of stars visible, the stars of Canis Major can be connected to form a convincing dog profile. He's currently prancing on his hind legs; he wears Sirius on his chest.

But through the light pollution where most of us live, only his five brightest stars are easily visible. These form a short-handled meat cleaver. Sirius is the cleaver's top back corner, its blade faces right, and its stubby handle is down to the lower left.

WEDNESDAY, FEBRUARY 17

■ The Moon shines below Mars this evening (by about 12° for North America). Look to the Moon's right by the same distance, and there are the brightest stars of Aries, magnitudes 2.0, 2.6, and 3.9 from top to bottom.

Above Mars by a lesser distance are the Pleiades.

THURSDAY, FEBRUARY 18

■ Mars shines over the Moon when the stars come out this evening, as shown below. Later in the evening the scene rotates clockwise with respect to your horizon, putting Mars to the Moon's upper right.

They appear only about 4° apart during evening for North America. In physical distance, though, Mars is 515 times farther away: 11 light-minutes compared to the Moon's 1.3 light-seconds. And, Mars is twice as large in diameter as the Moon.

FRIDAY, FEBRUARY 19

■ First-quarter Moon (exactly so at 1:47 p.m. EST). The Moon shines between Aldebaran and the Pleiades high in the evening, as shown above. The first-quarter Moon of February is always in their vicinity.

SATURDAY, FEBRUARY 20

■ Now spot Aldebaran below the Moon, as shown above.

■ Have you ever seen Canopus, the second-brightest star after Sirius? In one of the interesting coincidences known to devoted skywatchers, Canopus lies almost due south of Sirius: by 36°. That's far enough south that it never appears above your horizon unless you're below latitude 37° N (southern Virginia, southern Missouri, central California). And there, you'll need a very flat south horizon. Canopus crosses the south point on the horizon just 21 minutes before Sirius does.

When to look? Canopus is due south when Beta Canis Majoris — Murzim the Announcer, the star about three finger-widths to the right of Sirius — is at its highest due south over your landscape. That's probably sometime between 8 and 9 p.m. now, depending on how far east or west you live in your time zone. Look straight down from Murzim then.

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This Week's Planet Roundup

Mercury, Venus, Jupiter, and Saturn are very deep in the glow of sunrise. Venus this week sinks below any chance of spotting, but the other three are getting a little higher day by day. Mercury is still way too faint, but you might have a chance at Saturn and lower but brighter Jupiter. You'll need binoculars or preferably a wide-field telescope and a view down to the east-southeast horizon. The diagram below sets the scene on the 14th; it's for 20 minutes before sunrise at 40° north latitude. The farther south you are from there the better. Good luck!

Mars (magnitude +0.7, in eastern Aries) continues to fade. It shines pale yellow-orange high in the west-southwest right after dark, under the Pleiades. Left of the Pleiades shines Aldebaran, essentially the twin of Mars now in brightness as well as color. In a telescope Mars is only 7 arcseconds wide, but at least your scope should show its gibbous shape.

At Mars itself it's a busy time for arriving spacecraft. The United Emirates' Hope craft and China's Tianwen-1 braked into Mars orbit just a few days ago. NASA's Perseverance rover should land on February 18th.

Why are the missions bunched together? Because the minimum-energy transfer orbit to get from Earth to Mars becomes available only when the two planets arrange themselves a particular way with respect to each other every 2.14 years. Dedicated observers will recognize this as Mars's synodic period — the same as its average time from one opposition to the next.

Uranus (magnitude 5.8, in western Aries) is roughly 15° below Mars in early evening. In binoculars Uranus is a little pinpoint "star." But with an apparent diameter of 3.5 arcseconds, it's a tiny, fuzzy ball at high power in even a fairly smallish telescope with sharp optics — during spells of good seeing. Finder chart (without Mars).

Neptune is lost in evening twilight.

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

Eastern Standard Time, EST, is Universal Time minus 5 hours. (Universal Time is also known as UT, UTC, GMT, or Z time. For more see Time and the Amateur Astronomer.)

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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 sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger (and illustrated) 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."

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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

 

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