This Week’s Sky at a Glance

Mercury is fading and dropping day by day. Use binoculars in bright twilight.
The "supermoon" of June 22–23, 2013, appears just 7% larger than the average full Moon.
S&T: Sean Walker

Friday, June 21

  • As Mercury fades and descends below Venus day by day, how long can you keep it in view?

  • After dark, look for fire-colored Antares to the lower right of the bright Moon.

    Saturday, June 22

  • The largest full Moon of 2013 rises around sunset and shines all night. Tomorrow night it's almost as full and almost as large (for the longitudes of the Americas, since the Moon is exactly full at 7:32 a.m. Sunday morning EDT.) On both nights, though, this "supermoon" is only a trace larger than an average Moon: 7% wider. Read about the supermoon on our blog.

    Sunday, June 23

  • This is the time of year when the two brightest stars of summer, Arcturus and Vega, are about equally high overhead shortly after dark. Arcturus is toward the southwest, Vega toward the east.

    Arcturus and Vega are 37 and 25 light-years away, respectively, and represent the two commonest types of naked-eye stars: a yellow-orange K giant and a white A main-sequence star. They're 150 and 50 times brighter than the Sun — which, combined with their nearness, is why they dominate the evening sky.

    Monday, June 24

  • Look a third of the way from Arcturus to Vega for dim Corona Borealis, the semicircular Northern Crown. It has one moderately bright star, Alphecca (magnitude 2.2). Look two thirds of the way for the dim Keystone of Hercules, whose brightest star is magnitude 2.8.

    Tuesday, June 25

  • During bright twilight today and tomorrow, Venus forms an almost straight line with Pollux and Castor low in the west-northwest. Bring binoculars, and look for them to Venus's right. And can you still detect Mercury below Venus? It's nearly as far below Venus (6°) as Pollux is to the right.

    Wednesday, June 26

  • Now that it's summer, the Summer Triangle stands high in full glory after dusk. Its top star is bright Vega high in the east. Deneb is the brightest star to Vega's lower left. Farther to Vega's lower right is Altair. The Summer Triangle is big: 35° long. Where the sky is dark, you can see that the Milky Way runs through it.

    Thursday, June 27

  • The interesting binocular field around Antares holds the dim glow of the globular cluster M4, as many skywatchers well know. But do you also know about Rho Ophiuchi, the fine binocular triple star in the same field? It's the top star of a loop of five including Antares, as shown in Gary Seronik's Binocular Highlight column in the June Sky & Telescope, page 45.

    Friday, June 28

  • The Big Dipper, still high in the northwest, is moving a little lower now and starting to dip around toward the right. Follow the curve of its tail a little more than a Dipper-length left to bright Arcturus high in the southwest.

    Saturday, June 29

  • This is the time of year when the dim Little Dipper floats straight upward from Polaris (the end of its handle) after dark, like a helium balloon on a string escaped from a summer evening party.


    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.

    The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but that's less than one star in an entire telescopic field of view, on average. By comparison, Sky Atlas 2000.0 plots 81,312 stars to magnitude 8.5, typically one or two stars per telescopic field. Both atlases include many hundreds of deep-sky targets — galaxies, star clusters, and nebulae — to hunt among the stars.
    Sky & 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).

    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 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.


    This Week's Planet Roundup

    Mercury is becoming a real challenge, rapidly fading and dropping below Venus very low in bright twilight. Bring binoculars. What's the last day you can keep it in view?

    Venus (magnitude –3.8) is gaining altitude very gradually, low in the west-northwest in evening twilight. Use binoculars to pick up Pollux and Castor off to its upper right or right.

    Mars and Jupiter remain hidden in the glare of the Sun.

    Saturn (magnitude +0.5, in Libra) glows in the south to southwest during evening, with slightly dimmer Spica 12° to its lower right after dark. Look about equally far to Saturn's left for Alpha Librae.

    See our telescopic guide "Scrutinizing Saturn" in the May Sky & Telescope, page 50, or the shorter version on our website. 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 in the east, and Neptune (magnitude 7.9 in Aquarius) is higher in the southeast, before the beginning of dawn. Finder charts for Uranus and Neptune.


    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.


    Like This Week's Sky at a Glance? Watch our SkyWeek TV short, also playing on PBS.


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