This Week’s Sky at a Glance

Friday, July 12

The Moon comes back to join Venus under looming Leo after sunset. (Moon positions are exact for the middle of North America.)

  • The waxing crescent Moon, faint Regulus, and bright Venus form a curving line low in the western twilight, as shown at right.

    Saturday, July 13

  • Summery Scorpius struts in the south right after dark. Now is the time (before the Moon grows bright) to explore its Milky-Way-rich southern part, full of bright deep-sky objects. The northern part of Scorpius includes orange Antares and, to Antares's right, Delta Scorpii, a star that 13 years ago doubled in brightness and still rivals Antares for attention.

    Sunday, July 14

  • Do you live too far north to see Alpha Centauri? The nearest star for northerners is Barnard's Star, a red dwarf 6.0 light-years away in northern Ophiuchus. At magnitude 9.6 it's fairly easy in most telescopes. See the article, finder charts and photo in the July Sky & Telescope, page 48.

    Monday, July 15

  • First-quarter Moon (exact at 11:18 p.m. EDT). Look quite close to the Moon for Spica. Saturn glows off to their upper left. Think photo opportunity.

    The Moon occults (hides) Spica for skywatchers in Hawaii and parts of Central and South America; see map and timetables.

    Tuesday, July 16

  • This evening the Moon shines below Saturn, with Spica now off to their lower right.

    Wednesday, July 17

  • The Moon stands in central Libra this evening, about midway (for the longitudes of the Americas) between Saturn to its right and the stars of upper Scorpius to its left.

    Thursday, July 18

  • Look lower left of the gibbous Moon this evening for the red supergiant Antares. Also nearby are other stars of upper Scorpius.

    Friday, July 19

  • Telescope users observing the waxing gibbous Moon from most of North America tonight can watch the Moon's invisible dark limb creep up to and occult the 4.4-magnitude star Xi Ophiuchi. Only Florida and the West miss out.

    Some times of the star's disappearance: in western Massachusetts, 12:38 a.m. EDT; Atlanta, 12:32 a.m. EDT; Chicago, 11:10 p.m. CDT; Winnipeg, 10:50 p.m. CDT; Kansas City, 11:00 p.m. CDT; Austin, 11:07 p.m. CDT; Denver, 9:39 p.m. MDT. Start watching early.

    Saturday, July 20

  • Look upper left of the Moon after dusk, by roughly three fists at arm's length, for Altair, the bright eye of Aquila the Eagle. Less far to the Moon's right is Antares, the fiery heart of Scorpius.


    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).

    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 is hidden in the glow of sunrise.

    Double-shadowed Saturn. Saturn is near eastern quadrature during July and August (90° east of the Sun), so this is when its globe casts the widest shadow onto the rings behind, as seen from Earth's viewpoint. That's the black band on the rings just off the globe at lower right of center (celestial northeast).

    Meanwhile, the rings are now casting an almost equally prominent shadow onto the globe. That's the black rim above the rings (south here is up). Both add to Saturn's 3-D appearance in a telescope.

    The gray band on the globe just inside the rings is the semitransparent C Ring, the sparse "Crepe Ring," with no shadow currently behind it to confuse its appearance.

    Damian Peach shot this extraordinarily fine image through excellent seeing conditions on July 8th.


    Venus (magnitude –3.9) shines brightly low in the west-northwest in evening twilight. In a telescope it's still small (12 arcseconds) and gibbous (87% sunlit). But for the rest of the year, watch it grow in size and wane in phase until becoming a long, ultra-thin crescent.

    Mars and Jupiter are low in the east-northeast during early dawn. Jupiter is far and away the brightest at magnitude –1.9. Look just upper right of it for Mars, magnitude +1.6. Binoculars help. Jupiter is drawing closer to Mars daily. They'll pass just 3/4° apart on the morning of July 22nd.

    Saturn (magnitude +0.6, in Virgo) glows in the southwest after dusk, with Spica 12° to its lower right. Look about as far to Saturn's left for fainter Alpha Librae. Just ½° above Saturn this week is dim Kappa Virginis, magnitude 4.3.

    Uranus (magnitude 5.8 in Pisces) and Neptune (magnitude 7.9 in Aquarius) are high in the southeast and south, respectively, before the beginning of dawn. 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.


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