This Week’s Sky at a Glance, May 20 – 28

Moon, Mars, Saturn, and Antares on the evenings of May 20, 21, and 22

The bright evening Moon forms very different geometrical patterns with Mars, Saturn, and Antares on Friday, Saturday, and Sunday evenings May 20, 21, and 22. . . .

Moon, Mars, Antares, and Saturn in early dawn, May 21-23

. . . And the following mornings, if you're up really early, the Moon flags the Mars-Antares-Saturn triangle sinking away low in the southwest.

Friday, May 20

• The nearly full Moon looms low in the east-southeast at sunset and shines above Mars as twilight fades. How soon can you pick out Mars? How much later will it be until you can pick out fainter Antares, rising 8½° below Mars?

And what about Saturn, 7½° left of Antares? Saturn and Antares rise at the same time if you're near 35° N latitude (North Carolina, central California). If you're north of there Saturn rises first; south of there, Antares.

And how soon can you spot the second-brightest star in this area? It's Delta Scorpii, now just 1° below Mars. That's less than a finger-width at arm's length.

Saturday, May 21

Mars is at opposition tonight, opposite the Sun as seen from Earth. It's almost at its closest to Earth for this apparition, though not exactly so until the 30th.

• Full Moon this evening; by coincidence, the Moon and Mars are both at opposition. The Moon forms a rough rectangle with Mars to its right or lower right, Antares farther below it, and Saturn to its lower left, as shown above (seen from North America). Think photo opportunity.

Sunday, May 22

• The Moon now rises in twilight with Saturn about 4° to its right (as seen from North America). Mars and Antares are farther to their right, as shown above.

Monday, May 23

• As spring grows late, the "Spring Star" Arcturus shines very high in the southeast after dark (very high over Mars). The "Summer Star" Vega, equally bright, dominates the sky lower toward the east-northeast.

Arcturus is a type-K1.5 giant and thus shines pale orange-yellow, like a drop of rich ginger ale. Below Mars is Antares, an M1.5 supergiant with a deeper fire color than Arcturus. Mars currently looks much yellower than Antares, at least to my eyes, but that's probably because it's so much brighter. Brightness makes any color look desaturated (more toward white) — an illusion of human color vision and camera chips too.

• Jupiter's Great Red Spot transits Jupiter's central meridian around 10:45 p.m. EDT. It's positioned in excellent view for an hour before and after it transits.

Tuesday, May 24

• Jupiter's moon Europa crosses Jupiter's face tonight from 9:24 p.m. to 12:12 a.m. EDT, followed by its especially tiny black shadow from 11:57 p.m. to 2:40 a.m. EDT. (Subtract 3 hours to get PDT.)

Wednesday, May 25

• The enormous Arch of Spring is sinking ever lower in the west. As twilight fades, its top pair of stars, Pollux and Castor, still stand high in the west-northwest. Look for the Arch's left end, Procyon, about two fists at arm's length lower left of Pollux. Farther to the lower right of Castor is its right end: little Menkalinan and then brilliant Capella.

• Jupiter's Great Red Spot transits Jupiter's central meridian tonight around 12:23 a.m. EDT.

Thursday, May 26

• With summer less than a month away (astronomically speaking), the last star of the Summer Triangle rises above the eastern horizon at the end of twilight. That's Altair, the lower-right corner of the Triangle. Its highest and brightest corner is Vega. The third is Deneb, sparkling less far to Vega's lower left.

Friday, May 27

• Have you been watching the Mars-Antares-Saturn triangle change shape? It's lengthening as Mars moves westward against the stars, away from the head of Scorpius. This will continue until the end of June. Then Mars will start to slingshot back to fly right between Antares and Saturn in late August. Plan to watch this slow summer drama.

• Jupiter's Great Red Spot transits Jupiter's central meridian tonight around 2:02 a.m. EDT; 11:02 p.m. PDT. It's positioned in excellent view for an hour before and after.

Saturday, May 28

• Constellations seem to twist around fast as they pass your zenith, if you're comparing them with the direction "down." Just a week ago the Big Dipper floated horizontally in late twilight an hour after sunset as seen from 40° N latitude. Now it's tilted almost 45° at that time, bowl down. Another two weeks and it will be hanging straight down by its handle at that time.

• Jupiter's Great Red Spot transits Jupiter's central meridian around 9:54 p.m. EDT.

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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 new Jumbo Edition for easier reading in the night. Click image for larger view.

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 new 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

Mars on April 19, 2016

Mars was 14.4 arcseconds wide on April 19th when Phil Miles of Queensland, Australia, took this image with a 20-inch reflector. South is up. Dark Sinus Sabaeus and Sinus Meridiani extend in from the left (preceding). The pointy peninsula a bit farther right is the Oxia Palus region. Lower right from there are big Niliacus Lacus and Mare Acidalium. The North Polar Cap has almost shrunken away in the northern-hemisphere summer. Clouds appear in the wintry far south and especially around the morning limb.

Jupiter on May 15, 2016

Jupiter as imaged by Christopher Go on May 15th with a 14-inch scope. South is up. The Great Red Spot remains vivid. Dark material lines the Red Spot Hollow like eye shadow.

Saturn on March 19, 2016. Damian Peach photo.

Saturn's rings are wide open this season, tipped 26° to our line of sight and extending above the planet's north and south poles. Damian Peach took this image with a 14-inch Schmidt-Cass on March 19th. South is up.

Mercury and Venus are hidden in the glare of the Sun.

Mars (magnitude –2.0, at the head of Scorpius) reaches opposition Saturday night May 21–22. It's closest to Earth on May 30th. After dark, orange-yellow Mars shines in the southeast almost as brightly as white Jupiter high in the southwest.

Look for Antares about 9° lower left of Mars during evening, and Saturn 7° or 8° to the left of Antares. The Mars-Antares-Saturn triangle stands highest in the south around 1 or 2 a.m.; this is the best time for telescopic viewing of the two planets. By early dawn the triangle is low in the southwest, now with Saturn over Antares.

In a telescope all this week and next, Mars appears 18.4 to 18.6 arcseconds in diameter, its biggest and best until July 2018. See our telescopic guide to Mars, with map, in the April Sky & Telescope, page 48, or the version online. And set our Mars Profiler for your time and date. If you're ambitious and have a big scope, now's the time to try hunting Phobos and Deimos, the two tiny Martian moons, using the June Sky & Telescope, page 48.

Jupiter (magnitude –2.2, in southern Leo) stands high in the south in twilight, then starts declining toward the southwest. See our telescopic guide to Jupiter in the March Sky & Telescope, page 48.

Saturn (magnitude +0.1, in southern) shines lower left of Mars closer to the left of Antares in the evening. The three cross the southern sky through the night, and by dawn they're low in the southwest. Saturn is nearing its own opposition on June 2nd. See our telescopic guide in the June Sky & Telescope, page 48.

Uranus is veiled by the glow of dawn.

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

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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