This Week’s Sky at a Glance, July 31 – August 8

Friday, July 31

• This evening, skywatchers in the Americas see the Moon rise about a half day past when it's exactly full. Can you detect the slightest out-of-roundness in the Moon's profile yet?

• Look high above the Moon for bright Altair. Above Altair by just a finger-width at arm's length is its orange sidekick Tarazed, 3rd magnitude and far in the background.

• All month, look about 5° left of Saturn in the south-southwest after dusk for the fine telescopic double star Beta (β) Scorpii. Left or upper left of Beta by 1.6° is another fine double, Nu Scorpii (not quite bright enough to be plotted below). High power in excellent seeing may reveal Nu as the Southern Double-Double.

Saturn and Scorpius on Aug. 1, 2015

Saturn stays essentially fixed with respect to the stars of Libra and Scorpius this week. That's because it reaches the stationary point of its retrograde loop on August 2nd.

Saturday, August 1

• The Moon, now between Capricornus and Aquarius, is 1½ days past full (for the Americas) when it rises in evening twilight. Its slight waning gibbous phase is now more definite.

• Today is Lammas Day or Lughnasadh, one of the four traditional "cross-quarter" days midway between the solstices and equinoxes. Sort of. The actual midpoint between the June solstice and the September equinox this year comes at 8:29 a.m. August 7th Eastern Daylight Time (12:29 UT). That's the exact center of astronomical summer.

Sunday, August 2

• The tail of Scorpius is low due south right after dark. How low depends on how far north you live. Look for the two stars especially close together in the tail. These are Lambda and fainter Upsilon Scorpii, known as the Cat's Eyes. They're canted at an angle; the cat is tilting his head and winking. See the illustration above.

The Cat's Eyes point west (right) by nearly a fist-width toward Mu Scorpii, a much tighter pair known as the Little Cat's Eyes. Can you resolve Mu without using binoculars? (It's shown as single on the illustration above.)

Monday, August 3

• Altair shines high in the southeast after dark. Just above it is little orange Tarazed. A bit more than a fist-width to Altair's left, look for Delphinus, the Dolphin, leaping leftward.

Tuesday, August 4

• The red long-period variable star Chi Cygni is having a bright maximum! It was reported at magnitude 4.3 as of July 30th and may still be on the way up. See the article and comparison-star chart in the August Sky & Telescope, page 51.

Wednesday, August 5

• The Big Dipper hangs diagonally in the northwest at nightfall. Most of its stars are about 80 light-years away. Follow the curve of its handle around left by a little more than a Dipper-length and there's bright Arcturus, due west. Arcturus is the nearest orange giant, 37 light-years away.

Mars below Castor and Pollux at dawn, August 8, 2015.

Use binoculars during dawn these mornings to look for Mars below Castor and Pollux.

Thursday, August 6

• Last-quarter Moon (exact at 10:03 p.m. EDT). The Moon rises around midnight in Aries, far below that constellation's leading stars.

• Now that the evening is moonless, explore the telescopic sights of Scutum with Sue French's Deep-Sky Wonders column, charts, and photos in the August Sky & Telescope starting on page 54.

Friday, August 7

• The Moon, just past last quarter, rises around 1 a.m. tonight. By early dawn Saturday morning it's high in the east, forming a triangle with Aldebaran to its lower left and the Pleiades farther to its upper left.

• In early dawn these mornings, use binoculars to look for Mars below Castor and Pollux, as shown at right.

Saturday, August 8

• Seeing any early Perseid meteors yet? The Perseid shower should peak late on the night of August 12–13. The sky will be moonless.


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.

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 (meaning 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

Saturn on July 18, 2015

Saturn as imaged by Christopher Go on July 18th. South is up. For small scopes, the most apparent feature on the globe is the contrast between the bright Equatorial Zone and the darker North Equatorial Belt.

Mercury, Venus, and Jupiter are very deep in the glow of sunset.

Mars (dim at magnitude +1.7) is just becoming visible low in the glow of dawn. Look for it a little above the east-northeast horizon 30 or 40 minutes before your local sunrise. Bring binoculars. Don't confuse it with similar-looking Pollux above it, or Castor above Pollux.

Saturn (magnitude +0.4, in Libra) shines in the south-southwest at nightfall, to the right of upper Scorpius. Fiery orange Antares, less bright, twinkles 13° to Saturn's left or lower left. Delta Scorpii is the brightest star sort of between them.

Uranus (magnitude +5.8, in Pisces) and Neptune (magnitude +7.8, in Aquarius) are in the southern sky 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) is Universal Time (UT, UTC, or GMT) minus 4 hours.


“This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours.”

— Neil deGrasse Tyson, 2014


2 thoughts on “This Week’s Sky at a Glance, July 31 – August 8

  1. AimeeprozAimeeproz

    We are wondering what to expect to see on Thursday 13th night time til dawn. Is there any special way we should watch? If so what way and what is the best time? We plan on having a great time with a blanket and a bottle if wine with a so so telescope.

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