This Week’s Sky at a Glance, August 25 – September 2


Moon and Jupiter, Aug 24 - 26, 2017

Post-eclipse, the Moon is back in the evening sky as a waxing crescent, retreating farther from our sunward line of sight.

Moon over Scorpius and Saturn, Aug. 28-30, 2017

Waxing further, the Moon passes over Scorpius and Saturn.

Jupiter and Spica low at dusk, Sept. 1, 2017

Jupiter is getting harder to see low in the afterglow of sunset.

Venus, Mars, Mercury at dawn, Sept. 2, 2017

Using binoculars, try for little Mars, super-faint Mercury, and Regulus very low under Venus as dawn grows bright.

Friday, August 25

• Look low in the west in twilight for the waxing crescent Moon, innocently sidling away from its blackout of the Sun four days ago. It forms a triangle with Jupiter and Spica, both of them below it, as shown here.

• In the early dawn of Saturday the 26th, spot Venus very low in the east. This morning it forms a straight line with Castor and Pollux, above it or to its upper left.

Saturday, August 26

• The thickening crescent Moon, no longer so shy, points its round side down nearly toward Jupiter low in twilight, as shown here.

Sunday, August 27

• Look for bright Vega passing the zenith as twilight fades away this week, if you live in the world's mid-northern latitudes. Vega goes right through your zenith if you're at latitude 39° north (near Baltimore, Kansas City, Lake Tahoe, Sendai, Beijing, Athens, Lisbon).

Monday, August 28

• The Moon this evening, barely short of first quarter, forms a wide triangle with Saturn to its right and Antares twinkling below the midpoint between them.

Tuesday, August 29

• First-quarter Moon (exact at 4:13 a.m. EDT on this date). By evening, can you see that the Moon is just a trace more than half lit? After dark it forms a triangle with Saturn to its left and Antares a greater distance below it.

Wednesday, August 30

• Now the Moon forms a diagonal line with Saturn and Antares to its lower right. Antares appears about three times as far from the Moon as Saturn does, as shown here.

Thursday, August 31

• The wide W pattern of Cassiopeia is tilting up in the northeast after dark. Look below the W's last segment on the lower left, by a little farther than the segment's length, for an enhanced spot of the Milky Way's glow if you have a dark enough sky. Binoculars will show this to be the Perseus Double Cluster — even through a fair amount of light pollution.

• Venus and the Beehive: Just before the first light of dawn on Friday morning (in other words, about 90 minutes before your local sunrise), spot Venus shining brightly low in the east-northeast. Binoculars will show the Beehive star cluster only about 1° to its left.

Friday, Sept. 1

• At nightfall, the waxing gibbous Moon is about equally distant from Saturn, well off to its right, and Altair, high to its upper left.

• A dawn challenge: As morning twilight brightens tomorrow (Saturday September 2nd), use binoculars to look for the triangle of Mars, Regulus, and Mercury very low in the east, far beneath Venus, as shown below. The three are only magnitudes 1.8, 1.4, and a really challenging 3.2, respectively. And that's before atmospheric extinction. Good luck!

Saturday, Sept. 2

• As twilight fades away into night, look far above the Moon for Altair. Much closer above the Moon (more or less), binoculars will show the wide double stars Alpha and Beta Capricorni. Alpha is the yellow-orange pair on top. The Beta pair is more unequal and probably harder to resolve.


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

Saturn on June 12, 2017, by Damian Peach and colleagues at Pic du Midi Observatory.

Saturn on June 12, 2017, captured by the crack June 2017 Pic du Midi planetary imaging team using the observatory's historic 1-meter f/17 reflector. Processed by Damian Peach. North is up.

Uranus from Pic du Midi June 12, 2017

The team also captured Uranus the same night, with white in its southern hemisphere. North is up.

Mercury is very deep in the sunrise, and very faint to boot, as shown above.

Venus (magnitude –3.9) shines in the east before and during dawn. Look for Pollux and Castor, much fainter, above it. Look for Procyon to its right. The triangle that Venus makes with Pollux and Procyon changes each morning.

Mars (magnitude +1.8) is also faint and very deep in the sunrise.

Jupiter (magnitude –1.7, in Virgo) is very low in the west-southwest during twilight. Look for fainter Spica (magnitude +1.0) 4° lower left of it; binoculars help.

Saturn (magnitude +0.4, in the legs of Ophiuchus) glows steadily in the south-southwest at nightfall. Antares, less bright, twinkles 12° to Saturn's lower right.

Uranus (magnitude 5.7, in Pisces) and Neptune (magnitude 7.8, in Aquarius) are well up in the east and southeast, respectively, by late evening. Inside them it likely rains diamonds. Use our 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 when challenged by antibiotics. Science and critical thinking 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."
— John Adams, 1770


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