Sky at a Glance | July 16th, 2010

The waxing gibbous Moon crosses upper Scorpius on Tuesday and Wednesday. These scenes are 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. For clarity, the Moon is shown three times actual size.

Friday, July 16

  • Look for Saturn and Mars to the right of the Moon at nightfall.

    Saturday, July 17

  • This week, face east as the stars come out and look very high; the brightest star there is Vega. Deneb is the brightest star to Vega's lower left, by 2 or 3 fist-widths at arm's length. Farther to Vega's lower right is Altair (with little Tarazed just above it). Vega, Deneb, and Altair form the big Summer Triangle.

    Sunday, July 18

  • First-quarter Moon (exact at 6:11 a.m. Eastern Daylight Time).

    Monday, July 19

  • Bright Vega passes highest overhead around midnight daylight saving time this week, depending on your longitude within your time zone. (How accurately can you time when Vega does this?) How close to the zenith Vega passes depends on your latitude. Vega goes exactly overhead if you're at north latitude 39°: Washington DC, St. Louis, Kansas City, Lake Tahoe.

    Tuesday, July 20

  • The brightest star in the west after dark is Arcturus, slowly moving lower now as summer advances. To its right in the northwest, the Big Dipper is swinging down into proper dipping position.

    Wednesday, July 21

  • After dark, look to the right of the waxing gibbous Moon for Antares and other stars of upper Scorpius, as shown above.

    Thursday, July 22

  • Jupiter's Great Red Spot should cross the planet's central meridian (the line down the center of Jupiter's disk from pole to pole) around 1:10 a.m. Friday morning Eastern Daylight Time, when Jupiter will be well up in the sky for observers the U.S. eastern time zone. See our full list of all Red Spot transit times for the rest of 2010.

    Friday, July 23

  • Saturn's wild, weird moon Titan is west of Saturn this evening. A small telescope will show it (at 9th magnitude). Follow Titan as it swings back and forth in orbit around Saturn every 16 days. Saturn's rings, meanwhile, still appear very narrow, but they've widened a trace in the last several weeks to 3° from edge on — even as the entire Saturnian system has been shrinking into the distance.

    Saturday, July 24

  • A line from Deneb through Altair (the longest side of the Summer Triangle) points down nearly to the Moon this evening.


    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).

    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 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 your 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

    Mercury (about magnitude –0.2) is low in the glow of sunset. Look far to the lower right of Venus.

    Venus (magnitude –4.2, in Leo) is the bright Evening Star sinking in the west as twilight fades. Between Venus and Mercury, can you see fainter Regulus?

    Mars (magnitude +1.4, at the Leo-Virgo border) is upper left of Venus. Watch Mars closing in on Saturn to its upper left day by day. In a telescope Mars is just a tiny blob 5 arcseconds in diameter.

    Jupiter on July 17, 2010
    Jupiter's Great Red Spot and the smaller Oval BA ("Red Spot Junior") are drawing closer together and should pass each in the coming weeks or months. Oval BA is just to the Great Red Spot's upper right here. South is up.


    Notice too that the dark South Equatorial Belt (just below the Great Red Spot) is starting to reappear, in a thin and irregular way, along with what may be part of the Red Spot Hollow. This image is one of a series that Christopher Go took on July 17th. Click for his animation of 10 images spanning 47 minutes as Jupiter rotated.


    Jupiter (magnitude –2.6, in Pisces) rises around 11 p.m. daylight saving time. It shines high in the southeast in the early morning hours and reaches its highest point in the south during early dawn. It's the brightest starlike point in the morning sky.

    Saturn (magnitude +1.1, in the head of Virgo) is in the west during evening, just upper left of slightly dimmer Mars. The diagonal line of Saturn, Mars, Venus, Regulus and Mercury continues to shrink. The first three of these planets will bunch up low in the sunset in early August.

    Uranus (magnitude 5.8, in Pisces) is 3° west of Jupiter. In a telescope Uranus is only 3.6 arcseconds wide, compared to Jupiter's 44″.

    Neptune (magnitude 7.8, at the Aquarius-Capricornus border) is up in good view by midnight, well to Jupiter's west. See our finder charts for Uranus and Neptune in 2010.

    Pluto (magnitude 14, in northwestern Sagittarius) is high in the south-southeast after dark. See our big Pluto finder charts for 2010 — though the moonlight interferes with such a faint object this week.


    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 (also known as UT, UTC, or GMT) minus 4 hours.


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