This Week’s Sky at a Glance, June 23 – July 1


Moon, Pollux, Castor on June 25, 2017

Binoculars will help you pick out Pollux and Castor to the right of the crescent Moon low in bright twilight on Sunday evening the 25th. Their visibility in a bright sky is exaggerated here.

Moon and Regulus, June 27, 2017

Two days later the thickening Moon passes Regulus . . .

Moon, Jupiter, Gamma Virginis June 30, 2017

. . .and then on the 30th at first quarter, the Moon puts on a show with Jupiter and especially Gamma (γ) Virginis. (The Moon's position in these scenes is always plotted exact for latitude 40° N, longitude 90° W, near the middle of North America. The Moon is always shown three times its actual apparent size.)

Friday, June 23

• This is the time of year when, after dark, the dim Little Dipper floats straight upward from Polaris (the end of its handle) — like a helium balloon on a string escaped from a summer evening party. Through light pollution, all you may see of the Little Dipper are Polaris at its bottom and Kochab, the lip of the Little Dipper's bowl, at the top.

• New Moon (exact at 10:31 p.m. EDT).

Saturday, June 24

• This is the time of year when the two brightest stars of summer, Arcturus and Vega, are equally high overhead soon after dark: Arcturus toward the southwest, Vega toward the east.

Arcturus and Vega are 37 and 25 light-years away, respectively. They represent the two commonest types of naked-eye stars: a yellow-orange K giant and a white A main-sequence star. They're 150 and 50 times brighter than the Sun, respectively — which, combined with their nearness, is why they dominate the evening sky.

Sunday, June 25

• By the time it's fully dark this week, Altair shines well up in the east. Helping to identify it is its little sidekick Tarazed (Gamma Aquilae), a finger-width above it or to its upper left. (They're unrelated; Altair is 17 light-years from us; Tarazed is about 460.)

Look left of Altair, by hardly more than a fist width, for the compact little constellation Delphinus, the Dolphin.

Monday, June 26

• The tiny black shadow of Io crosses Jupiter's face tonight from 10:23 p.m. to 12:33 a.m. EDT, when it leaves Jupiter's western limb. Then just three minutes later, Europa exits from in front of the western limb.

Tuesday, June 27

• This evening, spot 1st-magnitude Regulus within 1° or 2° of the waxing crescent Moon (for North America).

Wednesday, June 28

• Do you know about the dark Propeller in the familiar M13 star cluster in Hercules? See Sue French's Deep-Sky Wonders column in the July Sky & Telescope, page 54.

Thursday, June 29

• The central stars of the constellation Lyra, forming a small triangle and parallelogram, dangle to the lower right from bright Vega high in the east. The two brightest stars of the pattern, after Vega, are the two forming the bottom of the parallelogram: Beta and Gamma Lyrae, Sheliak and Sulafat. They're currently lined up vertically. Beta is the one on top.

Friday, June 30

• First-quarter Moon (exact at 8:51 p.m. EDT). The "star" left of the moon is Jupiter.

• And this evening, the Moon's dark limb will occult (cover) the bright, tight double star Gamma Virginis (Porrima) for much of the U.S. and Canada. The event happens in daylight for the West, twilight for the central longitudes of the continent, and later in darkness for the East.

See more in the July Sky & Telescope, page 50. Here are detailed timetables for hundreds of cities and towns. (The UT date of the event is July 1st.) Plan ahead!

Saturday, July 1

• The Moon this evening forms a broad triangle with Jupiter and Spica in the southwest.


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 11, 2017

This just might be the sharpest image of Saturn ever taken from the ground. Damian Peach and six colleagues acquired it on June 11th using the 1-meter Pic Du Midi reflector high in the French Pyrenees. "Rarely seen details are observed, such as small ringlets within Ring C, including the Maxwell and Colombo divisions," writes Peach. "The Encke division is easily observed around the entire [outer] A ring. Note the strong blue colouration of the southern hemisphere shining through the Cassini division." South is up.

Jupiter with Io and Europa in transit, June 16, 2017

If you've wondered why you can't see Io and Europa in your scope when they're crossing Jupiter's face, it's because they're about the same brightness and color as Jupiter itself. The top tick points to Io, the bottom tick to Europa. Christopher Go took this image at 10:55 UT June 16, 2017. South is up.

Mercury and Mars are buried deep in the glow of sunset.

Venus (magnitude –4.2) shines brightly in the east before and during dawn.

Jupiter (magnitude –2.1, in Virgo) shines brightly in the southwest during evening. Spica, magnitude +1.0, glitters 11° left of it. In a telescope, Jupiter has shrunk to 38 arcseconds wide.

Saturn (magnitude 0.0, in southern Ophiuchus) glows pale yellowish in the southeast to south during evening. Fiery Antares, less bright, is 15° to Saturn's right or lower right. Delta Scorpii, the third brightest object in the area, catches the eye half that far to the upper right of Antares.

Uranus (magnitude 5.9, in Pisces) is well up in the east before the beginning of dawn.

Neptune (magnitude 7.9, in Aquarius) is higher in the southeast before the beginning of dawn.


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. Vaccines do stop diseases. Carbon dioxide does warm 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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