Sky at a Glance | May 18th, 2012

Friday, May 18

  • Arcturus is the brightest star high in the southeast these evenings. It's the leading light of the constellation Bootes, the Herdsman. The main stars of Bootes form a narrow, bent kite shape extending left of Arcturus, nearly three fists at arm's length long. Or maybe the kite is a pointy-toed shoe, with Arcturus the tip of the toe.

    Saturday, May 19

  • Venus is moving lower in the west every evening as twilight fades. It's now 2° left of much fainter Beta Tauri, which has been descending almost in parallel with it.

    Different locations, different eclipse views
    Nearly all North America gets at least a partial eclipse on May 20th, with the Moon taking a big bite out of the Sun. The eclipse will still be in progress at sunset for much of the U.S., Canada, and Mexico. Article.

    Sunday, May 20

  • Partial/annular eclipse of the Sun! This afternoon, all but easternmost North America will experience at least a partial eclipse of the Sun. So will the Pacific and (on the morning of May 21st local date) the eastern half of Asia. The eclipse will become annular — with the rim of the Sun a brilliant ring surrounding the dark silhouette of the Moon — along a path from south China and parts of Japan across the Pacific to the California-Oregon coast and from there southeastward to end at sunset in Texas.

    See our article, May 20th's Annular Eclipse of the Sun, which has links to more detailed maps, local timetables, and many other resources, including How to Watch Safely. Warning: Looking at any part of the bright Sun without a proper, safe solar filter can permanently damage your vision.

  • Arcturus shines high in the southeastern sky after dark. Vega, equally bright, shines lower in the northeast. A third of the way from Arcturus to Vega, look for dim Corona Borealis, the Northern Crown, with its one modestly bright star, Alphecca. Two thirds of the way from Arcturus to Vega is the dim Keystone of Hercules.

  • New Moon (exact at 7:47 p.m. Eastern Daylight Time).

    Bright twilight
    Day by day the waxing Moon marches up away from the Sun, even as Venus moves (more slowly) down toward the Sun. Visibility of the faint objects in bright twilight is exaggerated; bring binoculars. As always, the scene is exact for the middle of North America: at latitude 40° N, longitude 90° W. The Moon is shown three times its actual apparent size.

    Monday, May 21

  • Can you pick up this month's thin crescent Moon yet? During twilight in the Americas it's barely 24 hours old. (After all, it was in front of the Sun yesterday afternoon!) Using binoculars, look for it no more than a half hour after sunset well below Venus in the west-northwest, as shown at lower right.

    Tuesday, May 22

  • After sunset, look for the thin two-day-old Moon left of Venus, as shown here.

    Wednesday, May 23

  • Using the Moon and Venus as your guides, what fainter stars in the area can you identify with the chart here? Binoculars help.

    Thursday, May 24

  • This evening Pollux and Castor are lined up above or upper right of the crescent Moon.

    Friday, May 25

  • Well to the right of the Moon shine Pollux and Castor. Look well below the Moon for Procyon.

    Saturday, May 26

  • By nightfall, the summer constellation Scorpius is rising in the southeast. You'll first spot orange-red Antares, the Scorpion's heart. Antares' two "outrigger" stars are just below it and to its upper right. Farther upper right is the diagonal three-star row of Scorpius's head.


    Want to become a better amateur astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

    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. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

    Sky Atlas 2000.0 (the color Deluxe Edition is shown here) plots 81,312 stars to magnitude 8.5. That includes most of the stars that you can see in a good finderscope, and typically one or two stars that will fall within a 50× telescope's field of view wherever you point. About 2,700 deep-sky objects to hunt are plotted among the stars.
    Alan MacRobert

    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 the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts effectively.

    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 classic if dated Burnham's Celestial Handbook.

    Can a computerized telescope replace charts? I don't think so — not for beginners, anyway, and especially not on mounts and tripods that are less than top-quality mechanically (able to point with better than 0.2° repeatability). As Terence Dickinson and Alan Dyer say in their invaluable 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

    Crescent Venus waning in May
    Seen in a telescope, Venus in the western dusk is enlarging in diameter while waning in phase. It's moving down Sunward, swinging (in its faster orbit) toward the line between Earth and Sun. The 10° scale refers to Venus's height above the horizon 45 minutes after sunset.

    Mercury is buried in the glare of the Sun.

    Venus (magnitude –4.5, in Taurus) is the bright "Evening Star" in the west-northwest in twilight. It's dropping lower every day; see article Venus Takes the Plunge.

    Look for Capella 20° to Venus's upper right (not shown here). Look just 2° or 3° to Venus's right or upper right for fainter Beta Tauri.

    In a telescope, Venus is a dramatic, thin crescent becoming more interesting all the time. This week it enlarges from 50 to 54 arcseconds tall while waning from 10% to just 4% sunlit. You may even see the crescent with firmly braced binoculars.

    Venus is plunging toward inferior conjunction, when it will transit the face of the Sun on June 5–6 (on the afternoon of the 5th for North America); for details see our article Transit of Venus. This will be the last Venus transit until 2117.

    Mars (magnitude +0.3) shines orange under the belly of Leo. It's high in the south-southwest at dusk and lower in the southwest to west later in the evening. Spot Regulus 10° or 12° to Mars's right in twilight, and to its lower right later. They're moving farther apart daily. Fainter Gamma Leonis is 8° above Regulus; the three form a triangle. Mars in a telescope is gibbous and very small (about 8.5 arcseconds wide), fading and shrinking.

    Jupiter is buried deep in the glow of sunrise.

    Saturn (magnitude +0.3, in Virgo) shines high in the south after dark. Spica, fainter and bluer, is nearly 5° to Saturn's lower right early in the evening, and directly below it later.

    Uranus (magnitude 5.9, at the Pisces-Cetus border) is very low in early dawn.

    Neptune (magnitude 7.9, in Aquarius) is low in the east-southeast before dawn's first light.


    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 Daylight Time (EDT) equals Universal Time (also known as UT, UTC, or GMT) minus 4 hours.


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