This Week’s Sky at a Glance, May 19 – 27

This Week’s Sky at a Glance, May 19 – 27

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Supernova for amateur scopes in a northern galaxy. On May 14th amateur Patrick Wiggins discovered a fresh supernova at magnitude 12.8 in NGC 6946, a showpiece galaxy at the Cepheus-Cygnus border. Story and charts: Bright Supernova Discovered in ‘Fireworks Galaxy’ NGC 6946. Update May 18th: Supernova 2017eaw, as it's now named, has brightened by 0.2 magnitude in the last 3½ days — not much.

Friday, May 19

• With the Moon gone from 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).

The cluster's brightest members form an inverted Y. The whole group Is about 5° wide — a big, dim glow to the unaided eye when seen in a 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 rises above the eastern horizon around 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, less far to Vega's lower left.

Waning Moon, Venus and Mercury at dawn, May 22=23, 2017

The waning crescent Moon hangs low with Venus and Mercury at dawn. (The visibility of Mercury is exaggerated here; binoculars will help.)

Sunday, May 21

• Arcturus, 30° to the upper right of Jupiter after dusk, is the second-brightest point of light on the southern side of the sky. The brightest star low in the northeast is Vega.

Look a third of the way from Arcturus to Vega for the delicate semicircle of Corona Borealis, the Northern Crown, with its brighter gem star Alphecca.

Two thirds of the way from Arcturus to Vega is the dim Keystone of Hercules.

• Telescope challenge: Catch the fast-pulsing star VX Herculis, an old RR-Lyrae-type variable, rising from 11th to 10th magnitude tonight in the course of about an hour (roughly 3:30 May 22nd UT). See our article, comparison-star chart, and timetable in the June Sky & Telescope, page 48.

Monday, May 22

• Look east in early dawn Tuesday morning for Venus with the waning crescent Moon, as shown above. And can you make out Mercury yet? (In these scenes, the Moon is always shown three times its actual apparent size.)

Tuesday, May 23

• Jupiter stands smack on the meridian (i.e. due south) in late twilight this week. Twilight can be an excellent time for observing a planet telescopically. Most of them are bright enough to show all the detail that your scope can resolve even through the deep blue of late twilight, when the planet's glare will be less dazzling. And in bright twilight after sunset or before sunrise, the atmospheric seeing sometimes steadies down markedly.

That also makes this a good time to observe the binary star Gamma Virginis, now just 3½° to Jupiter's upper right. The pair's separation this season is a pretty easy 2.6 arcseconds.

Moon and Mars at dusk, May 26-28, 2017

The waxing crescent Moon returns to the evening sky, guiding the way to low Mars.

Wednesday, May 24

• Summer Milky Way preview: For much of every spring at mid-northern latitudes, the Milky Way lies right down all around the horizon after dark, completely out of sight. But as evening grows late, watch low in the east to northeast. There the rich Cygnus stretch of the Milky Way now starts rising into view by around 10 or 11 p.m. It will rise earlier and higher every week.

Thursday, May 25

• A double shadow transit on Jupiter is visible tonight from 10:47 p.m. to 12:19 a.m. Pacific Daylight Time, when both Io and Europa are casting their slightly unequal little shadows onto the planet.

• New Moon (exact at 3:44 p.m. EDT).

Friday, May 26

• While twilight is still bright, can you catch the thin crescent Moon just above the west-northwest horizon about to set? The Moon is only about 1 1/4 days after new as seen at the time of dusk for North America; see the time of new Moon yesterday above. And how about little Mars to its upper right?

Saturday, May 27

• The thickening crescent Moon, now below the heads of the Gemini twins, shines near Gamma (γ) Geminorum: the brightest star in the twins' feet.

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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.

Mercury (about magnitude +0.2) is deep in the glow of sunrise, even though is was at greatest elongation on May 17th. Look for it about 20° lower left of Venus. If you spot Mercury, you've succeeded in seeing it during its poorest apparition of the year!

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

Mars (magnitude +1.7, in Taurus) glimmers very low in evening twilight. Look for it just above the west-northwest horizon, 22° (two fists at arm's length) lower left of Capella. Mars passes between the horn-tips of Taurus (Beta and Zeta Tauri, magnitudes 1.6 and 3.0) on May 27th. The three will form a diagonal line 8° long from upper right to lower left. Binoculars will help.

Jupiter (magnitude –2.3, in Virgo) glares high and bright in the southern sky during evening. No other point is nearly so bright. Spica, noticeably bluer, glitters 11° lower left of it. In a telescope, Jupiter is starting to shrink as Earth pulls ahead of it in our faster orbit around the Sun. It appears 42 arcseconds wide this week.

Saturn (magnitude +0.1, at the Ophiuchus-Sagittarius border) rises around the end of twilight and glows highest in the south in the early-morning hours. Redder Antares (magnitude +1.0) twinkles 17° to Saturn's right or lower right. Saturn will reach opposition on the night of June 14th.

Uranus (magnitude 5.9, in Pisces) is still hidden in the glow of dawn.

Neptune (magnitude 7.9, in Aquarius) is low in the east-southeast before the first light of dawn.

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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.

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"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

"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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