This Week’s Sky at a Glance, July 18 – 26

Waning Moon at dawn

The waning crescent Moon at dawn passes Aldebaran and the Hyades. . .

Friday, July 18

Last-quarter Moon (exact at 10:08 p.m. Eastern Daylight Time). The Moon rises around midnight tonight, shining in Pisces.

Early Saturday morning before dawn, the faint asteroid 611 Valeria will occult an 8.7-magnitude star in Pisces for observers along a track crossing northern Mexico, Texas, the Deep South (including the Atlanta area) and the Carolinas. Details, times, finder chart.

Saturday, July 19

Mars at dusk is still slightly less than 3° (two finger widths at arm's length) from Spica in the southwestern sky. But they're widening and sinking lower day by day.

Sunday, July 20

In a 6- or 8-inch telescope, globular star clusters are among the most beautiful objects in the night and certainly among the eeriest. This is their season. Fred Schaaf describes his pick of the "the Fabulous Five" for amateur scopes in the July Sky & Telescope, page 47.

Monday, July 21

As dawn begins very early early Tuesday morning the 22nd, look for Aldebaran near the waning crescent Moon in the east as shown above. Can you catch the Hyades stars before dawn gets too bright?

Tuesday, July 22

Vega is the brightest star very high in the east. Far down to its lower right shines Altair, almost as bright. Altair is flagged by little Tarazed a finger-width above it, an orange-giant star far in Altair's background.

Moon and Venus in the dawn

. . . on its way to passing Venus lower down two mornings later. (The visibility of the fainter objects in bright twilight is exaggerated here. 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.)

Wednesday, July 23

As dawn brightens on Thursday morning the 24th, spot Venus low in the east-northeast with the waning crescent Moon to its right and Mercury still to its lower left, as shown here.

Thursday, July 24

In a really dark sky, the Milky Way now forms a magnificent arch high across the whole eastern sky after darkness is complete. It runs all the way from below Cassiopeia in the north-northeast, up and across Cygnus and the Summer Triangle in the east, and down past the spout of the Sagittarius Teapot in the south.

Friday, July 25

Mars and Spica still shine low in the southwest as night comes on. Mars keeps pulling farther away from Spica; they're now 6° apart. Saturn glows to their upper left. Arcturus sparkles high to their upper right.

Saturday, July 26

Summer is hardly more than a third over, astronomically speaking. But already the Great Square of Pegasus, symbol of the coming fall, heaves up from behind the east-northeast horizon at dusk and climbs higher in the east through the evening. It's balancing on one corner.


Want to become a better astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby; 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).

Pocket Sky Atlas

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but it's still less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae.

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 once you know your way around, 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, which means fairly heavy and expensive). 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 –0.5 and brightening) is low in the glow of sunrise, to the lower left of brighter Venus. Watch Mercury pull farther down and away from Venus this week.

Venus (magnitude –3.8) shines low in the east-northeast during dawn, far below Capella.

Mars (magnitude +0.3, in Virgo) is high in the southwest at dusk. Spica shines to its lower right; their separation is widening now. In a telescope, Mars's tiny gibbous disk is only 8.5 arcseconds tall.

Jupiter is hidden from sight in conjunction with the Sun.

Sharp view of Saturn, June 1, 2014

Christopher Go took this extraordinarily sharp image of Saturn during excellent seeing with a 14-inch scope on June 1st. Note the growing shadow of the globe on the rings (just off the globe's lower-right edge), and the shadow of the rings on the globe (just above the rings' edge at top).

Saturn (magnitude +0.5, in Libra) shines in the south-southwest in twilight, to the upper left of the Mars-Spica pair. After dark, look for fainter Alpha Librae lower right of Saturn, and Beta Librae about twice as far above Saturn.

Uranus, in Pisces, and Neptune, in Aquarius, are well up in the southeast and south before the first light of dawn. Use our finder charts for Uranus and Neptune.

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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) is Universal Time (UT, UTC, or GMT) minus 4 hours.