This Week’s Sky at a Glance, July 28 – August 5

Moon, Jupiter, and stars July 27, 28, 29, 2017

Watch the Moon pass the lineup of Spica, Jupiter, and Gamma (γ) Virginis from night to night.

Friday, July 28

• Jupiter shines under the Moon this evening, more or less as drawn here (their exact placement will depend on your location).

• The Sagittarius Teapot is in the south after darkness is complete. It's about a fist at arm's length wide, and it's now tilting to pour from its spout on the right. The Teapot will tilt farther and farther, pouring out for the rest of the summer — or for much of the night if you stay out late.

Saturday, July 29

• Lower right of the Moon at dusk, look for Spica. Right of Spica shines brighter Jupiter.

Sunday, July 30

• First-quarter Moon (exact at 11:23 a.m. EDT). The Moon is in Libra, far upper left of Spica and Jupiter at dusk, and far right of Scorpius and Saturn.

• Starry Scorpius is sometimes called "the Orion of Summer" for its brightness and its prominent red supergiant (Antares in the case of Scorpius, Betelgeuse for Orion). But Scorpius passes a lot lower in the south than Orion for those of us at mid-northern latitudes. That means Scorpius has only one really good evening month: July, which is almost over.

Catch Scorpius in the south-southwest now right after darkness is complete, before it tilts lower toward the southwest. It's full of deep-sky objects for binoculars or a telescope — if you have a detailed star atlas to find them with. (See the Pocket Sky Atlas below.)

The tail of Scorpius curves low to the lower left of the Scorpion's bright head and main body. How low depends on how far north or south you live: the farther south, the higher Scorpius appears. 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.

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 takes very sharp vision!

Monday, July 31

• The Big Dipper, still high in the northwest after dark, is turning around to "scoop up water" through the evenings of summer and early fall.

Tuesday, August 1

• The waxing gibbous Moon this evening forms a triangle with Antares to its lower left and brighter Saturn more directly to its left, as shown here.

Wednesday, August 2

• Now the Moon poses with Saturn. Although they look close together, Saturn tonight is is 3,500 times farther away: 81 light-minutes distant, compared to the Moon's 1.3 light-seconds.

Thursday, August 3

• Saturn shines right of the Moon at dusk, and lower right of it as night grows late.

Friday, August 4

• As soon as it's dark, look lower right of the bright Moon for the Teapot of Sagittarius. It's about the size of your fist at arm's length, tilting to pour to the right from its spout.

Saturday, August 5

• The Moon shines low in the southeast as the stars come out. How early can you spot Altair, three fists at arm's length to the Moon's upper left? How about brighter Vega, nearing the zenith from the east?


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, jumbo edition

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but it's less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae. Shown above is the Jumbo Edition for easier reading in the night. Larger view. Sample chart.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or Jumbo Edition), which shows stars to magnitude 7.6.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many. The next up, once you know your way around, is 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, or the bigger Night Sky Observer's Guide by Kepple and Sanner.

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). And 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

Venus at dawn, July 29, 2017

Venus, shining brightly in early dawn, is still near the horns of Taurus at the beginning of the week, forming a big triangle with Aldebaran and Betelgeuse. . .

Venus at dawn, August 5, 2017

. . . but by week's end Venus has entered the feet of Gemini, and the triangle it forms with Aldebaran and Betelgeuse has morphed quite a bit. Venus is holding almost steady with respect to your dawn landscape, while the background stars slide to the upper right from morning to morning.

Saturn, about as it appears visually in an optically excellent 12-inch telescope during rock-steady seeing.

If you've been spoiled by the recent pix here from the pro-am planetary imaging teams using 1-meter telescopes in Chile and at Pic du Midi in France, this image taken with the 1-meter Chilescope on July 9th may not look like much. "Very poor seeing," writes Damian Peach. The image looks about like Saturn looks visually in a backyard scope a third that size (meaning a 12-inch) during excellent seeing. So I've shrunk it down to resemble the view in my own 12-inch reflector at 200x on the rare occasions when the seeing is rock-steady.
     South is up. The Cassini Division is visible all around, the outer A Ring and inner B ring brighten toward the division's edge, the dim, innermost C ring is perceptible with effort, and there's no sign of the Encke Gap. On the globe, the bright Equatorial Zone and darker North Equatorial Belt are easy. Click here for the Chilescope team's much larger full-size view (with north up).

Mercury fades from magnitude +0.2 to +0.6 this week and is also sinking lower in the afterglow of sunset. Look for it just above the due-west horizon 30 minutes after sundown.

Venus (magnitude –4.0) shines brightly in the east before and during dawn, as shown here. Watch the changing shape of the triangle it forms from morning to morning with fainter orange Aldebaran to its upper right and orange Betelgeuse rising to its lower right.

Mars is hidden behind the glare of the Sun.

Jupiter (magnitude –1.9, in Virgo) shines brightly in the west-southwest in early evening. Fainter Spica (magnitude +1.0) glitters 7° or 8° left of it. In a telescope, poor Jupiter has shrunk to 35 or 34 arcseconds wide as it swings toward the far side of the Sun from Earth's viewpoint.

Saturn (magnitude +0.2, in the legs of Ophiuchus) glows steadily in the south at nightfall. Fiery Antares, less bright, twinkles 13° to Saturn's lower right. Delta Scorpii, the third-brightest object in the area, catches the eye less far to the right or upper right of Antares.

Uranus (magnitude 5.8, in Pisces) and Neptune (magnitude 7.9, in Aquarius) are high in the southeastern sky in the hours before the first light of dawn. Finder charts.


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


"Objective reality exists. Facts are often determinable. Carbon dioxide warms the globe. Bacteria evolve in response to antibiotics. Science and reason are no political conspiracy. They are how we discover reality. Civilization's survival depends on our ability, and willingness, to do so."
— Alan MacRobert, your Sky at a Glance editor


"Facts are stubborn things; and whatever may be our wishes, our inclinations, or the dictates of our passions, they cannot alter the state of facts and evidence."
— John Adams, 1770


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