Sky at a Glance | May 20th, 2011

The view as dawn brightens
Now that Jupiter is higher and easier to see, you can use it as a guide to locating the other three dawn planets.

These scenes are always drawn for 40° north latitude. If you're south of there, the view will be rotated counterclockwise by roughly your difference from 40° latitude. (The visibility of objects in bright twilight is exaggerated.)


Friday, May 20

  • As dawn brightens early Friday, Saturday, and Sunday mornings, Venus forms a right triangle a little more than 2° wide with Mercury below it and faint little Mars to its left, as shown here. Look very low in the east using binoculars.

    Saturday, May 21

  • Arcturus is the brightest star very high in the southeast after dark. Vega, equally bright, is much lower in the northeast. A third of the way from Arcturus to Vega, look for the dim semicircle of Corona Borealis, the Northern Crown, with its one moderately bright star, Alphecca.

    Two-thirds of the way from Arcturus to Vega, look for the dim Keystone of Hercules.

    Sunday, May 22

  • Faint Mars is passing about 1° above bright Venus this morning through Tuesday morning.

    Monday, May 23

  • Face northwest this evening and look high; there's the Big Dipper, now hanging down by its handle. Just a few weeks ago it was horizontal! Star patterns appear to change orientation fast when they pass near the zenith. The reason for this? When you're looking near the zenith, the directions toward "up" and "down" (toward and away from the zenith) differ a lot over short distances.

    Tuesday, May 24

  • Last-quarter Moon (exact at 2:52 p.m. EDT). The Moon rises long after midnight tonight daylight-saving time, beneath the head of Aquarius (the Water Jar asterism).

    Wednesday, May 25

  • The western twilight Arch of Spring is sinking lower, but you can still catch this big landmark when the stars come out. Pollux and Castor are lined up roughly horizontal in the west-northwest; they're about three finger-widths apart. Look far to their lower left for Procyon, and farther to their lower right for Capella.

    Thursday, May 26

  • Friday dawn lineup: Set the alarm so you can be looking toward the eastern horizon about 30 minutes before sunrise Friday morning. The waning crescent Moon hangs high; far lower left of it is Jupiter. Lower left of Jupiter (by 15°) is Venus, not high at all. With binoculars or a low-power scope, look for tiny, faint Mars 2° upper right of Venus and Mercury 4° lower left of Venus.

    Friday, May 27

  • With summer less than a month away, the big Summer Triangle is making its appearance in the east. Its topmost and brightest star is Vega, plain to see. Look lower left of Vega, by two or three fist-width at arm's length, for Deneb, the brightest star in that area. Farther to the lower right of Vega is Altair, the last of the three Summer Triangle stars to rise (around 10 or 11 p.m. daylight saving time, depending on your location).

    Dawn view
    Watch the Moon pass over the dawn planet lineup in the closing days of May. (The visibility of the fainter objects in bright twilight is exaggerated here. These scenes are always drawn for the middle of North America. European observers: move each Moon symbol a quarter of the way toward the one for the previous date.)

    Saturday, May 28

  • Before sunrise tomorrow morning, look for the waning crescent Moon hanging above Jupiter, as shown at right. Use binoculars to check out the changing planetary array to their lower left.

  • Late tonight a 7th-magnitude star in Ophiuchus should be occulted for up to 11 seconds by the faint asteroid 217 Eudora as seen from a track running from Florida through Oklahoma and Colorado to Oregon. See map, finder charts, and full information.


    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
    must have a detailed, large-scale sky atlas (set of charts). The standards are the Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger Sky Atlas 2000.0 (stars to magnitude 8.5); and the even larger and deeper 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 Sky Atlas 2000.0 Companion by Strong and Sinnott, or the more detailed and descriptive Night Sky Observer's Guide by Kepple and Sanner, or the classic if dated Burnham's Celestial Handbook.

    Can a computerized telescope take their place? I don't think so — not for beginners, anyway, and especially not on mounts that are less than top-quality mechanically. 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 May 19, 2011
    Jupiter is still too low in early dawn for sharp telescopic viewing, but Christopher Go obtained this image anyway on May 19th. It shows that Jupiter's dark South Equatorial Belt (above center) has returned and is now wide and bicolored, and that the North Equatorial Belt remains very prominently dark red-brown. Note the white oval in the north edge of the NEB, and long, narrow dark barge a little farther north. South is up.
    Christopher Go

    Mercury, Venus, Mars, and Jupiter continue their evolutions low in the dawn, but now they're drawing farther apart. Use binoculars about 30 minutes before sunrise; look low in the east. Jupiter is the highest. Look lower left of it for Venus. Near Venus, binoculars should show Mercury (below or lower left of Venus) and perhaps faint little Mars (left of or above Venus).

    See our article "The Four-Planet Dance of 2011" about this dawn parade, with daily panels in an animation. You can pause the animation at the date of your choice.

    Saturn (magnitude +0.6, in Virgo) is now in excellent evening view high in the south. Just ½° to its right is fainter Porrima (Gamma Virginis), turning Saturn into a naked-eye "double star." Shining 14° to Saturn's lower left is Spica.

    Saturn on May 12, 2011
    Saturn's white spot continues re-erupting! The head of the pale streamer wrapping around the planet has rebrightened with new upwelling material, as seen in this image taken by Christopher Go on May 12th (at 13:32 UT; System III central-meridian longitude 314°). "The old and new materials are interacting, forming bright and complex features," he writes. South here is up.


    Also see his gif animation or wmv animation of several more images taken over the course of 84 minutes, confirming dark spoke markings on the celestial east (following) side of the bright B ring. In the animations, north is up.

    In a telescope Saturn's rings are 7.3° from edge on, their minimum tilt for more than a decade to come. The rings are casting a relatively wide, prominent black shadow southward onto the globe, and the globe's shadow on the rings is visible just off the globe's celestial east (following) side, as seen in the image here. On the globe itself, Saturn's six-months-old white outbreak remains very active. Read Dissecting Saturn's Big Storm for in-depth results (literally) from the Cassini Saturn orbiter and the Very Large Telescope in Chile.

    See how many of Saturn's satellites you can identify in your scope using our Saturn's Moons tracker.

    And don't skip over Porrima. It's a fine, close telescopic binary star with a current separation of 1.7 arcseconds. Use high power and hope for good seeing. See the article in the April Sky & Telescope, page 56.

    Uranus (magnitude 5.9, in western Pisces) is very low in the east before the first light of dawn.

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

    Pluto (magnitude 14.0 in Sagittarius, and back here by popular request) is highest in the south before dawn. A finder chart for it, running from June 1st through the end of Pluto's observing season, will appear in the July Sky & Telescope, page 64.


    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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