Some daily events in the changing sky for May 23 – 31.

The bright International Space Station continues to have many good flyovers this week. Amaze your friends! Show them one of its passes above your hometown using our custom prediction generator.

Comet Boattini, about 6th magnitude, is visible this week from the southernmost US, the tropics, and the Southern Hemisphere, now that the Moon is out of the early-evening sky. The comet is crossing northern Pyxis and Puppis: low in the southwest right after dusk for the latitudes of the southern US. See our article and finder charts. It's been seen naked-eye from Australia.

Moon in early dawn

In early dawn later this week, the waning Moon marches past the Sagittarius Teapot and Jupiter. The scene is plotted for the middle of North America. European observers: move each Moon symbol a quarter of the way to the one for the previous date.

Sky & Telescope diagram

Friday, May 23

  • Mars is still crossing the Beehive Star Cluster this evening, as binoculars or a small telescope will reveal.
    See article and chart.

  • Early risers Saturday morning will find Jupiter below the waning gibbous Moon in the south, as shown at right.

    Saturday, May 24

  • A small telescope will always show Titan, Saturn's largest and wildest moon. Tonight Titan is four ring-lengths to Saturn's east. A guide to identifying all six of Saturn's satellites that are sometimes visible in amateur scopes is in the May Sky & Telescope, page 60.

    Sunday, May 25

  • The Mars Phoenix Lander is scheduled to touch down on a flat, far-northern plain of Mars around 7:53 p.m. EDT. Watch the NASA TV coverage of the event on the web starting at 6:30 p.m. EDT. Full schedule.

    Monday, May 26

  • Moonwatchers! A favorable libration for elusive Mare Orientale, the unique formation on the Moon's celestial-east limb, begins Tuesday morning and runs through Sunday morning. See the May Sky & Telescope, page 66.

    Tuesday, May 27

  • Last-quarter Moon (exact at 10:57 p.m. EDT).

    Wednesday, May 28

  • The Big Dipper has flung its handle high over its bowl (face northwest after dark and look almost overhead), so this is a fine time to check out the asterisms and galaxies in the handle's vicinity. See Sue French's Deep-Sky Wonders column, "Flying off the Handle," in the June Sky & Telescope, page 70.

    Thursday, May 29

  • The red long-period variable star R Virginis should be at its maximum light this week: an easy-in-binoculars 6th magnitude.

    Friday, May 30

  • Look northeast after nightfall this week and there will be bright Vega, sparkling pale blue-white. It's by far the brightest star of the little constellation Lyra, shown below. The rest of Lyra's main pattern is made of 4th-magnitude stars that form a little, nearly equilateral triangle with Vega, and a parallelogram dangling to the triangle's lower right. Is your sky dark enough for Lyra to show? It's about the length of your thumb at arm's length.

    Saturday, May 31

  • Have you turned your telescope on Porrima yet this year? For more than a century Porrima, or Gamma Virginis, has been a renowned double star for small scopes. But in the last few years its components have been so close together that the star has appeared single for the first time since the 1830s. Now they're widening again: to 1.0 arcsecond apart now and 1.1″ in September. Can you resolve them yet? You'll need a sharp 4- or 6-inch scope and a night of excellent seeing. Keep watch for the rest of your life; Porrima will widen for the next 80 years.

    Don't know where it is? Get out your Sky & Telescope and turn to the monthly fold-out constellation chart. Porrima is the brightest star a little more than a fist-width to the upper right of Spica in the south after dark.

    Bright Vega dominates the little thumb-sized constellation Lyra, currently dangling to Vega's lower right.

    Akira Fujii

    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 foldout map in each issue of Sky & Telescope, the essential magazine of 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 maps; the standards are Sky Atlas 2000.0 or the smaller Pocket Sky Atlas) and good deep-sky guidebooks (such as Sky Atlas 2000.0 Companion by Strong and Sinnott, the even more detailed Night Sky Observer's Guide by Kepple and Sanner, or the classic Burnham's Celestial Handbook). Read how to use them effectively.

    More beginners' tips: "How to Start Right in Astronomy".

    This Week's Planet Roundup

    Jupiter on May 24, 2008

    Jupiter on May 24th. The North Equatorial Belt, above center, "is getting lighter in color from the deep dark red a few weeks ago," writes photographer Christopher Go. The black dot on it is the shadow of Io. Visible below center are not just one red spot but three; see picture below. The Great Red Spot remains near System II longitude 121°. North is up (though many telescopes show south up).

    Christopher Go

    Mercury and Venus are hidden in the glare of the Sun.

    Mars (magnitude +1.5, in Cancer) shines high in the west after dark, off to the upper left of the Castor-and-Pollux couple. Each week Mars is moving farther away from them and closer to the Saturn-and-Regulus couple to Mars's upper left. Mars, Saturn, and Regulus will have close get-together in early July.

    In a telescope, Mars is a minuscule 5.1 arcseconds wide — a very tiny blob.

    Jupiter (magnitude –2.6, in eastern Sagittarius) rises around 11 or midnight daylight saving time, left of the Sagittarius Teapot. It's highest in the south, and therefore sharpest in a telescope, shortly before dawn. (The table of Jupiter's satellite phenomena in the May Sky & Telescope is incorrect; use this corrected version.)

    The Hubble Space Telescope caught Jupiter's three red spots on May 10, 2008. They're closing in toward each other daily. The Great Red Spot is at right, Oval BA ("Red Spot Junior") is the lowest, and 2008 Oval 2 is at left. Color contrast is exaggerated. North is up. Read more.

    Even today, the cause of the coloring is not known for sure. The leading theory is that when a storm grows strong enough, it dredges up some compound from deep below the clouds and lofts it to unusually high altitude, where ultraviolet sunlight causes a chemical reaction that produces the red stuff. See full coverage of the recent Jupiter campaign by Hubble and Keck.

    Alan MacRobert

    In the last few weeks, planetary scientists have been using the Hubble and Keck telescopes for a coordinated, multi-wavelength observing campaign to track Jupiter's current upsurge of activity and to tackle its chemical mysteries. Start here.

    Saturn (magnitude +0.7, in Leo) glows high in the southwest after dark, 2½° above fainter Regulus (magnitude +1.4). They're quite the eye-catching couple, though they're gradually getting wider apart now.

    Telescope users: there's more to Saturn than you may realize! See our Saturn observing guide in the April Sky & Telescope, page 66.

    Uranus and Neptune (magnitudes 6 and 8, respectively, in Aquarius and Capricornus) are in the east and southeast just before dawn. Use our article and finder charts.

    Saturn with white spots

    In a large amateur scope during excellent seeing, a pair of white storms is visible in Saturn's South Temperate Zone. This stacked-video image was taken at 11:15 UT on May 1, 2008, when the System II longitude on the central meridian was 70°. North is up.

    To find when the white spots are back in view the same way as seen here: For your date (in Universal Time), look up Saturn's System II central-meridian longitude in this table (it's the "CMII" column). That's the value for 0:00 UT that date. To this value, add 33.8° for each whole hour since 0:00 UT, and 0.56° for each minute, for the time you plan to observe. See what you get. Find a good Saturn-observing date and time for you that results in something around 70°, and plan to be out then with your scope.

    P.S.: Here's an incredible closeup shot of the storm by Cassini taken on March 4th. And Cassini's radio instruments find that the storm is full of lightning.

    Christopher Go

    Pluto (magnitude 14.0, in northwestern Sagittarius) is well up in the southeast after midnight. If you've got a big scope and ambition to match, use our article and finder chart.

    All descriptions that relate to your horizon or zenith — 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 (UT, UTC, or GMT) minus 4 hours.

    "Rational and innocent entertainment of the highest kind."
    — John Mills, 19th century Scottish manufacturer and founder of Mills Observatory, on amateur astronomy.

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    • About Alan MacRobert

    Alan M. MacRobert became an avid Sky & Telescope subscriber in 1966 at age 14, joined the editorial staff in 1982, and is now a senior contributing editor, semi-retired. He played a role in practically every part of the magazine and the company's other products for more than a generation, both on the amateur-observing side and the science-reporting side. In 1994 a book collection of his observing how-tos and telescopic sky tours was published as Star Hopping for Backyard Astronomers. He has produced This Week's Sky at a Glance online every week since 1989.

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