Sky at a Glance | May 31st, 2013

Catch the Mercury-Venus-Jupiter lineup before it's too late! (As always, this scene is oriented for 40° north latitude. The fainter stars are hard to see in bright twilight. The frame is about three fist-widths at arm's length wide.)

Friday, May 31

  • Mercury, Venus, and Jupiter have stretched out into a nice straight line 7° long, as shown at right below. Look low in the northwest after sunset. The line will continue to lengthen day by day, as Jupiter descends to the horizon and Mercury pulls a bit higher above Venus.

  • Last-quarter Moon (exact at 2:58 p.m. EDT). The Moon rises around the middle of the night.

    Saturday, June 1

  • Vega, the brightest star in the east these evenings, is currently the top star of the huge Summer Triangle. Look to Vega's lower left, by two or three fists at arm's length, for Deneb. The third star of the Summer Triangle is Altair, considerably farther to Vega's lower right. Altair is just rising in the east as dusk fades away. How early in the evening can you spot it?

    Sunday, June 2

  • The best time to view Venus in a telescope is in late afternoon well before sunset, when it's still at a high altitude in relatively steady air. Mercury and Jupiter are in the same vicinity, but they're tougher catches in broad daylight. Pick them up them using the day-by-day finder chart for all three above the afternoon Sun in the June Sky & Telescope, page 51.

    Monday, June 3

    The horizon is positioned for viewers near latitude 40° north around the world.
  • "Cassiopeia" usually means "Cold!". Late fall and winter are when this landmark constellation is high overhead (seen from mid-northern latitudes), but even on hot June evenings it's lurking low. After dark, look for it down near the north horizon. It's a wide, upright W. The farther north you are the higher it'll appear. But even as far south as San Diego and Atlanta it's completely above the horizon.

    Tuesday, June 4

  • Above the Big Dipper's high handle is north-central Bootes, home to double stars, three spindle galaxies, and the Kangaroo asterism. Find them using Sue French's "Deep-Sky Wonders" article, map, and photos in the June Sky & Telescope, page 56.

    Wednesday, June 5

  • Vega is the brightest star in the east these evenings. The main part of its little constellation, Lyra, dangles from it to its lower right.

    Thursday, June 6

  • With June well under way, the Big Dipper has swung around to hang down by its handle high in the northwest after dark. The middle star of its handle is Mizar, with tiny little Alcor right next to it. On which side of Mizar should you look for Alcor? As always, on the side exactly toward Vega! Which is now shining in the east.

    Jupiter is gone now, but Mercury is about at its peak altitude. The blue 10° scale is about the size of your fist held at arm's length.

    Friday, June 7

  • Mercury has reached its farthest distance above Venus, 5°. See the twilight scene at right. This is the same separation as between fainter Pollux and Castor above them, which come into view as twilight fades further. 5° is about three finger-widths at arm's length (depending, of course, on the width of your fingers relative to the length of your arm!).

    Saturday, June 8

  • After dark, look southeast for orange-red Antares. It's one of the naked-eye sky's two great red supergiants; the other is Betelgeuse in winter. Around and upper right of Antares are the other, white stars of upper Scorpius.

  • New Moon (exact at 3:14 a.m. on this date EDT).


    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
    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

    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.

    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

    Mercury, Venus, and Jupiter are still visible in the afterglow of sunset, forming a straight line pointing downward just above the west-northwest horizon as shown at the top of this page. Venus is the brightest. Jupiter, the bottom one, becomes harder to see each day and is gone by the end of the week. Mercury on top is having its best evening appearance of 2013.

    On May 31st this line of three is 7° long and the planets are equally spaced. By June 5th the line is 13° long with Jupiter falling far away. See our article The May-June Planet Dance, with a video running all the way to June 20th.

    Mars is hidden behind the glare of the Sun.

    Saturn on April 20, 2013
    "Here is an image of Saturn taken on April 20th from Mt. Olympus, Cyprus (1950m altitude) under excellent observing conditions," writes Damian Peach. "Probably the best view I've had of the planet in the last few years. Periods of extremely steady seeing prevailed and allowed a very clear view of the planet and rings. A really memorable and enjoyable night on Cyprus's highest peak."


    North is up. Note the north polar hexagon. The thin whitish zone at mid-northern latitudes is the remains of the great storm of 2010–11. Several brightness minima can be seen across the ring system. Peach used a 14-inch Celestron Schmidt-Cassegrain telescope.


    Saturn (magnitude +0.2, in Libra) glows in the south during evening, with Spica to its right. In a telescope, Saturn's rings are tilted 17° 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 at the beginning of dawn.

    Neptune (magnitude 7.9, in Aquarius) is in the southeast before dawn begins. Use our 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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