Some daily events in the changing sky for August 15 – 23.

Friday, August 15

  • Neptune is at opposition.

    Saturday, August 16

  • Full Moon (exact at 5:16 p.m. EDT).

    Keep watching as Mercury closes in on Venus. On the 16th, it's equidistant between bright Venus and faint Saturn (for which you'll need binoculars).

    Sky & Telescope diagram

  • A partial eclipse of the Moon happens on the evening of the 16th or the morning of the 17th for most of the inhabited world — except North America! See our article and world map. The times of key events during the eclipse are shown in the diagram here, of the the Moon passing through Earth's shadow. Times are Universal Time (GMT) on the 16th.

    As for North America? It doesn't get even a partial lunar eclipse until June 26, 2010.

    Sunday, August 17

  • Jupiter's Great Red Spot should cross Jupiter's central meridian (the imaginary line down the center of the planet's disk from pole to pole) around 8:56 p.m. EDT, at nightfall on the East Coast. The "red" spot appears very pale orange-tan. It should be visible for at least 50 minutes before and after in a good 4- or 6-inch telescope if the atmospheric seeing is sharp and steady, which it usually isn't. A blue or green filter helps. For all Red Spot transit times, good worldwide, see our listing or applet online.

    Monday, August 18

  • As summer advances, the Big Dipper assumes its diagonal tilt high in the northwestern sky after dark. Bright Arcturus shines in the west, a little more than a Dipper-length to the left of the Dipper's handle.

    Tuesday, August 19

  • Venus and Mercury are within 1° of each other after sunset today, tomorrow, and Thursday. That's about a pencil-width at arm's length.

    This is just the beginning of an amazing series of conjunctions involving four of the five classical planets that continues well into September. Click here to view a one-megabyte movie of the four-planet dance. After watching the general progression, step forward and back to see the configuration on any particular evening. You may need to install QuickTime to watch the film if you haven't already done so.

  • Jupiter's Red Spot should transit around 10:35 p.m. EDT.

    Shortly after sunset

    Mercury and Venus appear closest on the 20th. Mars, meanwhile, is gradually moving toward them from the upper left day by day, and Saturn is fast disappearing to their lower right.

    Sky & Telescope diagram


    Wednesday, August 20

  • Venus and Mercury are closest (at appulse) today. They're 1° apart, as shown at right.

    Thursday, August 21

  • Jupiter's Red Spot should transit around 9:13 p.m. Pacific Daylight Time.
  • Callisto casts its tiny black shadow onto Jupiter's northern regions tonight from about 10:34 p.m. to 2:27 a.m. EDT. Meanwhile, Io disappears behind Jupiter's western limb at 11:35 p.m. EDT. Io then reappears out of eclipse from Jupiter's shadow at 2:49 a.m. EDT, just east of the planet.

    For a listing of all events among Jupiter's moons this month, visible worldwide, see the August Sky & Telescope, page 58.

    Friday, August 22

  • There's an interesting coincidence this season. Every night, bright Jupiter passes its highest due south right about when Vega passes highest overhead.
  • How good, or bad, is your sky? What's your naked-eye limiting magnitude for stars overhead? Find out using the head-of-Draco map in Fred Schaaf's article in the August Sky & Telescope, page 48.

    Saturday, August 23

  • Last-quarter Moon (exact at 7:50 p.m. Eastern Daylight Time).

    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

    Mercury (about magnitude –0.3) is in deep in the glow of sunset, very close to much-brighter Venus as shown in the scenes above. They're just 1° or 2° apart this week. Mercury and Venus will remain within 3° of each other through the end of August. Look with binoculars about 30 minutes after sunset.

    Venus (magnitude –3.8) is still deep in the glow of sunset. Look for it just above the west-northwest horizon about 30 minutes after sundown. Fainter Mercury is very close by, as shown above. Saturn, fainter still, is moving away to the lower right day by day. Look too for little Mars to the upper left.

    Mars (a dim magnitude +1.7) is low after sunset, roughly a fist-width at arm's length upper left of Venus. Use binoculars.

    Jupiter on Aug. 8, 2008

    Jupiter's Great Red Spot was nearing the planet's central meridian when Christopher Go took this stacked-video image at 12:23 UT August 8, 2008. The Great Red Spot remains near System II longitude 127°. To its upper left, the smaller Oval BA ("Red Spot Junior") has already crossed the central meridian. South is up, to match the south-up view in many telescopes.

    Click on the image for more views that night, including one resolving Ganymede and one taken in the infrared methane band. Methane in Jupiter's atmosphere absorbs this wavelength — so bright features indicate high-altitude clouds that are above most of the atmosphere.

    Christopher Go

    Jupiter (magnitude –2.6, in Sagittarius) shines brightly with a steady glare in the south after dark. It's upper left of the Sagittarius Teapot and just below the bowl of the smaller, dimmer Teaspoon. It's due south and highest around 9 or 10 p.m. daylight saving time.

    Saturn (magnitude +0.8) is sinking away to the lower right of brighter Venus and Mercury in the sunset, as shown in the panels above. Bring binoculars.

    Uranus and Neptune (magnitudes 5.7 and 7.8, respectively, in Aquarius and Capricornus) are well up in the southeast by 10 or 11 p.m. Use our article and finder charts.

    Pluto (magnitude 14.0, in the northwestern corner of Sagittarius) is in the south right after dark. If you've got a big scope and a dark sky, 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 (known as UT, UTC, or GMT) minus 4 hours.

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