This Week's Sky at a Glance
Some night sky sights for May 17 – 25
Chi Cygni bright. Chi (χ) Cygni, one of the brightest red long-period variable stars, has been having an unusually bright maximum. It's been about magnitude 3.8, very plain to the naked eye, and is now barely starting to decline. Look for it adding to the bottom part of the shaft of the Northern Cross, between Eta (η) and Beta (β) Cygni. Cygnus is reasonably well up in the east by about 11 p.m., with the Northern Cross lying on its side. Comparison-star chart and two-year light curve up to the present courtesy AAVSO.
Scale model: If the Moon were a BB at reading distance 14 inches in front of you, Regulus would be a house-size, white-hot fireball at the Moon's actual distance!
Saturday, May 18
Find Antares about three fists at arm's length to the lower left of Saturn. Along the way you'll pass fainter Alpha Librae (not far from Saturn), and not-so-faint Delta Scorpii (relatively close to Antares).
Sunday, May 19
Monday, May 20
These three planets about to swing through a "trio" together, as shown in the video below. They'll appear closest together in a tight little triangle, 2° on a side, next Sunday the 26th.
Wednesday, May 22
Thursday, May 23
This evening Venus and Mercury appear their closest together. But all three will fit in a circle just 2½° wide when they're grouped their tightest on Sunday.
Saturday, May 25
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 guide to astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).
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 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). 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
Venus (magnitude –3.9) is still quite low in the west-northwest in twilight, to the lower right of Jupiter. Watch as Venus and Jupiter draw together by about 1° per day. On May 17th they're still 11° apart. Their conjunction comes on the 28th, when they'll be 1° apart with Mercury right alongside.
Mars is hidden behind the glare of the Sun.
Jupiter (magnitude 1.9) is sinking lower in twilight every day as it approaches Venus. See our article on the Jupiter-Venus-Mercury show, The May-June Planet Dance.
Saturn (magnitude +0.2, in Libra) glows in the southeast in twilight. Spica is to its upper right, and Arcturus is twice as far to its upper left.
Saturn is highest in the south around 11 p.m. or so. In a telescope, its rings are nicely tilted 18° from our line of sight. See our guide "Scrutinizing Saturn" in the May Sky & Telescope, page 50, or the shorter version online. And identify Saturn's many moons at any time and date with our SaturnMoons utility or handier app.
Uranus (magnitude 5.9, in Pisces) is low in the east in early dawn.
Neptune (magnitude 7.9, in Aquarius) is in the southeast just before dawn begins.
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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