This Week’s Sky at a Glance, February 20 – 28

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

Venus, Mars and the Moon form a tight bunch as twilight fades on Friday, Feb. 20, 2015.

Venus, Mars, and the Moon form a tight bunch as twilight fades. (The Moon here is positioned for an observer near the middle of North America. It's drawn three times its actual apparent size.)

Conjunction of Mars and Venus, Feb. 21, 2015.

A day later Mars and Venus appear closest, with the thickening crescent now above them.

Friday, February 20

Venus, the thin crescent Moon, and little Mars form a tight bunch in the west-southwest during and after dusk, as shown at right. They fit in a circle just 2° across at the times of dusk for most of North America. Think photo opportunities! See our article, Venus and Mars Pair Tightly at Dusk.

We have just a few more days to follow Comet Lovejoy, still 5th magnitude, high in a moonless evening sky this month.

Saturday, February 21

Venus and Mars are in conjunction 0.4° apart at dusk, with the Moon now looking on from above.

Two mutual events among Jupiter's moons. Watch Europa pass in front of Io this evening, from 9:05 to 9:11 p.m. EST. Their combined light dims by 0.6 magnitude (not quite half) at the center of this time.

Then less than an hour later, Europa casts its shadow onto Io from 9:41 to 9:49 p.m. EST, dimming Io by 0.9 magnitude at the mid-time.

Watch Christopher Go's highly magnified videos of Europa occulting Io and then Europa eclipsing Io on February 18th. (The gray spot at the center of each satellite is a processing artifact.)

Sunday, February 22

Jupiter blazes in the east after dark this week. High above it are Pollux and Castor. Look about half as far to Jupiter's right for the dim head of Hydra, the Sea Serpent, about the width of your thumb at arm's length.

Before the Moon starts brightening the evening sky too much, take a telescopic tour through some of the Melotte star clusters with Sue French's Deep-Sky Wonders column, charts, and photos in the March Sky & Telescope, page 58.

Monday, February 23

Spot the Pleiades high above the Moon after dark. Look to the Moon's right, just a little less far, for the brightest stars of Aries lined up nearly vertically.

Tuesday, February 24

Soon after nightfall, look upper right of the Moon for the Pleiades and upper left of the Moon for Aldebaran and the Hyades.

One of the most famous challenge objects for amateur astronomers is Sirius B, Sirius's white-dwarf companion. The pair has been widening for the last two decades, and now Sirius B stands a good 10.7 arcseconds to Sirius's east. To try to extract it from the dazzlement of the 10,000-times-brighter primary star, see the tips and tricks in the March Sky & Telescope, page 50.

A much easier white dwarf is Omicron2 Eridani B, also described there and also now in the evening sky.

Wednesday, February 25

Look for Aldebaran shining near the first-quarter Moon.

Thursday, February 26

Watch Jupiter's satellite Europa reappear from eclipse out of Jupiter's shadow at 10:23 p.m. EST (7:23 p.m. PST), just off Jupiter's eastern limb.

Mercury is at greatest elongation low in tomorrow's dawn, 27° west along the ecliptic from the Sun.

Friday, February 27

Venus and Mars in the western twilight have widened to be 2.7° apart. Find faint little Mars beneath Venus now.

Saturday, February 28

Early this evening, the dark limb of the waxing gibbous Moon will occult (cover) the 3.6-magnitude star Lambda Geminorum for North America east of the Mississippi and north of the deepest South.

Some times: central Massachusetts, 8:00 p.m. EST; Washington DC, 7:56 p.m. EST; Chicago, 6:31 p.m. CST (in twilight); Kansas City, 6:21 p.m. CST (in twilight). See map and detailed timetables of both the disappearance and the (unobservable) reappearance; be careful not to mix these up when scrolling down the table.

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

Jupiter on February 18th, by <a href=

Mercury (magnitude 0.0) glimmers just above the east-southeast horizon in early dawn. As the sky brightens toward sunrise, you'll need binoculars.

Venus (magnitude –3.9) and Mars (less than 1% as bright, at magnitude +1.3) appear very close together in the west-southwest during evening twilight.

On Friday the 20th the crescent Moon joins them to make a beautiful bunch-up. On Saturday the 21st Venus and Mars are in conjunction, 0.4° apart with Mars just to Venus's upper right as seen from North America. In the following days, Mars moves down and away from Venus.

Jupiter (magnitude –2.6, in Cancer) is two weeks past opposition. Watch for it coming into view in the eastern sky early in evening twilight. As night falls, look to its left and lower left for the Sickle of Leo. By 9 or 10 p.m. Jupiter is nearly as high as it will get. In a telescope Jupiter is still a big 45 arcseconds wide at its equator.

Saturn (magnitude +0.5, at the head of Scorpius) rises around 2 a.m. It's best placed in the south as dawn begins. Below Saturn by 8° or 9° is orange Antares.

Look 1.6° to Saturn's lower right in early dawn for Beta Scorpii, magnitude 2.5, a showpiece double star for telescopes. Look much closer just below Saturn for fainter Nu Scorpii, a wider telescopic double.

Uranus (magnitude 5.8, in Pisces) is getting low in the west just after dark, to the upper left of Venus and Mars. Finder chart.

Neptune is hidden in conjunction with the Sun.

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.