Mercury in twilight, mid-July 2017
Binoculars will help with finding Mercury and its fainter neighbors. Their visibility in bright twilight is exaggerated here.

Friday, July 14

• Mercury is having a poor apparition low in evening twilight this month. But it's bright enough (magnitude –0.2 this evening) that you can pick it up anyway if the air is good and clear. Your best chance is probably about a half hour after sunset, as shown at right.

• One hour after sunset, as twilight is fading deeper and the stars are coming out, you'll find the two brightest stars of summer, Vega and Arcturus, high overhead equally far from the zenith: Vega toward the east, and Arcturus toward the southwest (depending on your location).

Saturday, July 15

• The tail of Scorpius is low in the south after darkness is complete. How low depends on how far north or south you live: the farther south, the higher. 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's hard!

Sunday, July 16

• 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.

• Last-quarter Moon (exact at 3:26 p.m. EDT). The Moon rises tonight around 2 a.m. daylight-saving time and is high in the southeast by Monday's dawn.

Monday, July 17

• If you have a dark enough sky, the Milky Way forms a magnificent arch very high across the whole eastern sky after nightfall is complete. It runs all the way from below Cassiopeia in the north-northeast, up and across Cygnus and the Summer Triangle high in the east below bright Vega, and down past the spout of the Sagittarius Teapot in the south.

Tuesday, July 18

• The first "star" you're likely to see coming out after sunset this month is bright Jupiter, in the southwest. Once you find it, examine the sky 30° above it (three fists at arm's length) for Arcturus, two magnitudes fainter.

Once the night is completely dark, look for the kite-shaped pattern of Bootes extending upper right from Arcturus. It's two fists long.

Moon and Venus at dawn, July 20, 2017
Set your alarm to catch the crescent Moon with Venus early in the dawn of Thursday the 20th.

Wednesday, July 19

• Early in Thursday's dawn, and even a bit earlier, Venus and the waning crescent moon shine together in the east, as shown here. Upper right of them is Aldebaran, and above Aldebaran are the Pleiades. Left of the Moon and Venus is 2nd-magnitude El Nath, Beta Tauri.

Thursday, July 20

• With the advance of summer, the Sagittarius Teapot, in the south after dark now, is starting to tilt and pour from its spout to the right. The Teapot will tilt farther and farther for the rest of the summer — or for much of the night, if you stay out very late.

Friday, July 21

• 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 is 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. Catch Scorpius due south just after dark now, before it starts to tilt 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 below).

Saturday, July 22

• We're only a third of the way through summer, but already W-shaped Cassiopeia, a constellation better known for fall and winter evenings, is climbing up in the north-northeast as evening grows late. And the Great Square of Pegasus, emblem of fall, comes up to balance on one corner just over the eastern horizon.


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, 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 one taken with the 1-meter Chilescope on July 9th may not look like much. "Very poor seeing," writes Damian Peach. The image looks more 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 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 (magnitude 0) is very low in west about a half hour after sunset. Good luck.

Venus (magnitude –4.1) shines brightly in the east before and during dawn. Aldebaran, much fainter at magnitude +0.9, moves away from Venus's right toward the upper right this week.

Mars is hidden behind the glare of the Sun.

Jupiter (magnitude –1.9, in Virgo) shines brightly in the west to southwest in early evening. Spica (magnitude +1.0) glitters 9° left of it. In a telescope, Jupiter has shrunk to 36 arcseconds wide.

Saturn (magnitude +0.2, in the legs of Ophiuchus) glows steadily in the south during and after dusk. Fiery Antares, less bright, twinkles 13° to Saturn's lower right. Delta Scorpii, the third brightest object in the area, catches the eye half that 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 side of the sky before the beginning 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. Bacteria evolve in response to antibiotics. Carbon dioxide warms the globe. 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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