This Week’s Sky at a Glance, April 29 – May 7

Friday, April 29

• Last-quarter Moon (exact at 11:29 p.m. EDT). The Moon rises tonight around 2 a.m. local daylight-saving time. It shines above dim Capricornus before the first light of dawn.

• It's a busy night at Jupiter. Io crosses the planet's face from 9:42 to 11:57 p.m. EDT, followed by its tiny black shadow from 10:44 p.m. to 12:58 a.m. EDT. Europa transits the planet from 12:28 to 3:25 a.m. EDT, followed by its shadow from 2:47 to 5:32 a.m. EDT.

Meanwhile, Jupiter's Great Red Spot crosses the planet's meridian around 10:52 p.m. EDT. (Subtract three hours from all times to get PDT.)

Saturday, April 30

• These evenings, the long, dim sea serpent Hydra snakes far across the southern sky. Find his head, an asterism about the width of your thumb at arm's length, in the southwest. It's to the lower right of Regulus by about two fists at arm's length. Hydra's tail reaches all the way to Libra rising in the southeast. His star pattern, from forehead to tail-tip, is 95° long.

Sunday, May 1

• Even though May has begun, wintry Sirius still twinkles very low in the west-southwest at the end of twilight (for mid-northern skywatchers). It sets soon after. How much longer into May can you keep Sirius in view? What will be its date of "heliacal setting" as seen by you?

The Mars-Saturn-Antares triangle in early dawn. (The blue 10° scale is about the width of your fist at arm's length.)

• All week, the Mars-Saturn-Antares triangle awaits intrepid skywatchers in early dawn, as shown at right.

Monday, May 2

• Two famous galaxies are detectable with good binoculars off the handle of the Big Dipper, if your skies are pretty dark. See Gary Seronik's guide to M51 and M101 in the Binocular Highlights for the May Sky & Telescope, page 43.

And with a telescope, explore galaxies under the Dipper's bowl starting on page 54.

Tuesday, May 3

• Bright Jupiter stands high due south at dusk. To its right is the Sickle of Leo, upright with Regulus marking the bottom of its handle. The Sickle's second-brightest star is Algieba, Gamma Leonis, a fine double star for telescopes. Before the Moon comes back into the evening sky, explore the faint galaxy groups around Algieba with Sue French's Deep-Sky Wonders article, charts, and photos in the April Sky & Telescope, page 54.

Wednesday, May 4

• The Eta Aquariid meteor shower should peak before local dawn Thursday morning, bit it's active for several mornings before and after as well. This is often the best shower of the year for the Southern Hemisphere. Mid-northern meteor watchers are less well placed and will see fewer. The sky is free of moonlight.

Thursday, May 5

• Summer is more than six weeks away, but the Summer Triangle is making its appearance in the east, one star after another. The first in view is Vega. It's already visible low in the northeast as twilight fades.

Next up is Deneb, lower left of Vega by two or three fists at arm's length. Deneb takes about an hour to appear after Vega does, depending on your latitude.

The third is Altair, which shows up far to their lower right around midnight.

Friday, May 6

• Double shadow transit on Jupiter. Both Callisto and Io cast their tiny black shadows onto Jupiter's sunlit face from 12:38 to 1:42 a.m. EDT tonight (9:38 to 10:42 p.m. PDT).

• New Moon (exact at 3:30 p.m. EDT; 12:30 p.m. PDT).

Can you catch the young Moon on Saturday evening the 7th? It becomes much easier to see when it's 24 and 48 hours older. (The Moon here is drawn three times its actual apparent size. The Moon positions are exact for near the middle of North America.)

Saturday, May 7

• Twenty or thirty minutes after sunset, try to catch the hairline crescent Moon just a few degrees above the west-northwest horizon, as shown here. Binoculars will help! Is this the youngest Moon you've ever seen? It's only about 28 hours from new as seen from the East Coast, 31 hours from new as seen from the Pacific time zone. (Calculate its age at the time of your sighting from the time of yesterday's new Moon, above.)

Aldebaran is a few degrees above or upper left of the delicate Moon. Which of the two is less difficult to see in binoculars? With the unaided eye?

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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.

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."

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This Week's Planet Roundup

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 April 19th, imaged at 12:56 UT by Christopher Go in the Philippines with a 14-inch Schmidt-Cass scope. South here is up. Europa, at right, is five minutes from crossing onto Jupiter's following (celestial eastern) limb. Io is most of the way across Jupiter's face, with its shadow following behind (because Jupiter is past opposition). Far south of Io is reddish Oval BA with a small gray spot following just behind it.

Jupiter's other side, imaged by S&T's Sean Walker on April 21st with a 12.5-inch scope. The Great Red Spot remains vivid. Dark clouds line the Red Spot Hollow.

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. But plan for the daytime transit of Mercury across the face of the Sun on Monday the 9th! See the May Sky & Telescope, page 48.

Mars is entering its closest and grandest two-month spell in a decade. This week Mars rises around 10 p.m. daylight-saving time, blazing at a Sirius-bright magnitude –1.5 in upper Scorpius. As it climbs higher, you'll find Antares 5° below it and Saturn 8° to its lower left. This striking triangle stands highest in the south around 3 a.m. (more than an hour before the first light of dawn), now with Saturn to Mars's left.

In a telescope this week, Mars grows from a very healthy 16 to 17 arcseconds in diameter as Earth continues to approach it. See our telescopic Mars guide in the April Sky & Telescope, page 48.

Mars will come to opposition on the night of May 21–22. For several days around its closest approach to Earth on May 30th, it will reach an apparent diameter of 18.6 arcseconds, its largest since 2005. (And at its next opposition and closest approach, in July 2018, it will grow to 24.3 arcseconds — nearly the largest we can ever see it.)

Jupiter (magnitude –2.2, in southern Leo) stands highest in the south at nightfall. Nothing else that high is nearly that bright. See our telescopic guide to Jupiter in the March Sky & Telescope, page 48.

Saturn (magnitude +0.2, between the legs of Ophiuchus above Scorpius) rises about a half hour after brighter Mars, following about 8° to Mars's lower left. By early dawn they stand in the south-southwest, with Saturn now upper left of Mars and fainter Antares about 5° below them.

Uranus is hidden in the sunrise.

Neptune is very low in the east-southeast as 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