This Week’s Sky at a Glance, May 12 – 20


Supernova for amateur scopes in northern galaxy. On May 14th UT, amateur Patrick Wiggins discovered a 12.8-magnitude supernova in NGC 6946, a showpiece galaxy at the Cepheus-Cygnus border. Spectra confirm that it's a young Type-II supernova probably still on the way up. For more info and charts, see Bright Supernova Discovered in ‘Fireworks Galaxy’ NGC 6946. Update May 18th: Supernova 2017eaw has brightened by a slight 0.2 magnitude in the last 3&frac1/2; days.

Venus at dawn, mid-May 2017

All this month you'll find the "Morning Star" low in the east as dawn brightens. Follow it with a telescope even after sunrise.

Friday, May 12

• The Arch of Spring spans the western sky in late twilight. Pollux and Castor form its top: they're lined up roughly horizontally in the west-northwest, about three finger-widths at arm's length apart. Look far to their lower left for Procyon, and farther to their lower right for Menkalinan and then bright Capella. The Arch of Spring is the last departing section of the even bigger Winter Hexagon.

Saturday, May 13

• Three zero-magnitude stars shine after dark in May: Arcturus high in the southeast, Vega much lower in the northeast, and Capella in the northwest. They appear so bright because each is at least 60 times as luminous as the Sun, and because they're all relatively nearby: 37, 25, and 42 light-years from us, respectively.

• In early dawn Sunday morning, look for Saturn lower right of the Moon. Much farther to the lower right of this pair is fiery Antares.

Sunday, May 14

• As twilight begins to fade, look very low in the west-southwest. Can you can still pick up Sirius, twinkling hard? The farther north you are, the harder it will be. Binoculars help. When is the final date you'll see Sirius at all?

Monday, May 15

• As the stars come out, face north and look almost straight up for the Big Dipper, now in its floating-upside-down position. Its handle curves in the direction toward bright Arcturus.

Tuesday, May 16

• Vega is the brightest star in the east-northeast after dark. Look 14° (about a fist and a half at arm's length) to Vega's upper left for Eltanin, the nose of Draco the Dragon. Closer above and upper left of Eltanin are the three fainter stars of Draco's stick-figure head, also called the Lozenge. Draco always points his nose to Vega. He seems curious about it.

Wednesday, May 17

• Summer Milky Way preview: For much of the spring at mid-northern latitudes, the Milky Way lies right down all around the horizon after dark, completely out of sight. But as night grows late, watch low in the east to northeast. There the rich Cygnus stretch of the Milky Way starts rising into view by around 11 p.m. It will rise earlier and higher every week.

Thursday, May 18

Jupiter double-shadow event for telescopes tonight: Io and smaller Europa are both casting their tiny black shadows onto Jupiter's face from 11:53 p.m. to 12:42 a.m. EDT.

• The last-quarter Moon rises around 2 a.m. tonight, shining in Aquarius. As Friday's dawn gets under way, look very high to the Moon's upper right for Altair, and look way off to the Moon's lower left for Venus making its appearance.

Friday, May 19

• With the Moon out of the evening sky, can you see the big Coma Berenices star cluster? Does your light pollution really hide it, or do you just not know exactly where to look? It's 2/5 of the way from Denebola (Leo's tail) to the end of the Big Dipper's handle (Ursa Major's tail).

Its brightest members form an inverted Y. The entire cluster is about 5° wide — a big, dim glow when seen in at least a moderately dark sky. It nearly fills a binocular view.

Saturday, May 20

• With summer still a month away (astronomically speaking), the last star of the Summer Triangle doesn't rise above the eastern horizon until about 10 or 11 p.m. That's Altair, the Triangle's lower right corner. Its highest and brightest corner is Vega. The third is Deneb, sparkling less far to Vega's lower left.


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

Jupiter on May 14, 2017

Jupiter on May 14th, imaged by Christopher Go in the Philippines. South is up. Note the recent new dark extension on the left (preceding) side of the Great Red Spot, and the unusually dramatic turbulence in the South Equatorial Belt on the spot's following side.

Saturn on April 29, 2017

Saturn on April 29th, imaged by Christopher Go. Again south is up. "The Polar Hexagon is distinct," Go writes. So is the small, dark blue-green polar spot in the middle of it, which Cassini imaged in a detailed closeup on April 26th.

Mercury is buried deep in the glow of sunrise, even though it's at greatest western elongation from the Sun on May 17th. This is its poorest apparition of the year.

Venus (magnitude –4.6) shines low in the east as dawn brightens. In a telescope it's a thick crescent.

Mars (magnitude +1.6, in Taurus) is finally sinking away in the western evening twilight, after a year-long apparition. Look for it far lower left of bright Capella high in the northwest. Don't confuse Mars with brighter Betelgeuse, which twinkles well to Mars's left due west.

Jupiter (magnitude –2.3, in Virgo) shines high and bright in the south-southeast at dusk, with Spica 10° lower left of it. Jupiter is highest in the south, for best telescopic viewing, soon after dark.

Saturn (magnitude +0.2, in Sagittarius) rises around 10 or 11 p.m. and glows highest in the south well before the first light of dawn. Redder Antares (magnitude +1.0) twinkles 18° to Saturn's right in the early-morning hours.

Uranus is hidden in the glow of dawn.

Neptune (magnitude 7.9, in Aquarius) is very low in the east-southeast before the first light 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 stop diseases. 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

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— John Adams, 1770


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