This Week's Sky at a Glance, May 1 – 9

Friday, May 1

■ As the stars come out this evening, look for Regulus under the Moon as shown below. The next brightest star in Leo's Sickle is yellow-orange Gamma Leonis, Algieba, also shown.

As the evening grows late, watch their arrangement rotate clockwise. And also watch the Moon creep slightly to the east with respect to the stars. As seen from Earth, the Moon moves along its orbit by about its own apparent diameter per hour.

■ All week, look high in the west at nightfall for Pollux and Castor, the heads of the Gemini twins. They're lined up almost horizontally (depending on your latitude), some 30° upper left of brilliant Venus: about three fists at arm's length.

Pollux and Castor form the top of the enormous Arch of Spring. To their lower left is Procyon, the left end of the Arch. Farther to their lower right is the other end, formed by Menkalinan (Beta Aurigae) and then brilliant Capella.

Venus shines below the Arch's right side.

Saturday, May 2

■ Although it's May now, wintry Sirius still twinkles low in the west-southwest in late twilight. It sets soon after. How much longer into the spring can you keep Sirius in view? In other words, what will be its date of "heliacal setting" as seen by you? A lot depends on your latitude: The farther north you are, the sooner it'll go.

Sunday, May 3

■ 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 (upper right of Venus). 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 away, respectively.

Monday, May 4

■ The brightest star below the Moon after dark is Spica. Farther to the Moon's left or upper left is brighter Arcturus.

Just 2° or 3° to the right of the Moon after dark for North America, look for fainter, 3rd-magnitude Gamma Virginis (Porrima). It's a fine, tight telescopic double star: two equal components currently separated by 3.0 arcseconds. Porrima is currently widening by 0.1 arcsecond each year.

■ The Eta Aquarid meteor shower should be at its peak in the hour or so before Tuesday's dawn. The Southern Hemisphere always has the best view of this shower, but this year even mid-northern skywatchers may be in for something a little special. Jupiter's gravity tugs on part of the meteor stream every 12 years, with the result that a richer part of the stream may intersect Earth this year and the next two.

But on the downside, the bright, nearly-full Moon doesn't set until after dawn is already in progress. So don't count on more than one meteor being visible every 5 or 10 minutes even if you're watching steadily, for instance by lying back in a lawn chair. See the May Sky & Telescope, page 50.

Tuesday, May 5

■ This evening, if you're in North America, draw a line from the Moon through Spica some 7° to its left or lower left. Continue the line on at least twice as far, and you're more or less at Corvus, the springtime Crow. Its four brightest stars have always been described in astronomy guides as "sail-shaped." That would be a sail that's gaff-rigged, a shape immediately recognized by our several-times-great-grandparents but less so now. What do you think this asterism might be in the 21st century? The Smashed Amazon Box?

Wednesday, May 6

■  Full Moon both this evening and tomorrow evening; the Moon is exactly full at 6:45 a.m. Thursday morning EDT. It's a supermoon, just a trace larger than average, because it's at perigee on the 6th.

As the stars begin to come out this evening, the Moon is low in the east-southeast. Look for Arcturus high to its upper left and Spica, not quite as bright, less far to the Moon's upper right.

Thursday, May 7

■  A gigantic asterism you may not know about is the Diamond of Virgo, some 50° tall and extending over five constellations. It now stands upright in the south after the stars come out. Start with Spica, its bottom. Upper left from Spica is bright Arcturus. Almost as far upper right from Arcturus is fainter Cor Caroli, 3rd magnitude. The same distance lower right from there is Denebola, the 2nd-magnitude tailtip of Leo. And then back to Spica.

The bottom three of these stars, the brightest, form a nearly perfect equilateral triangle. Maybe we should call this the "Spring Triangle" to parallel those of summer and winter?

Friday, May 8

■ The waning gibbous Moon rises in the east-southeast around 10 p.m. daylight-saving time, depending on where you live in your time zone. Once it's well up, look to its right or lower right for Antares, twinkling pale orange. Around and to the upper right of Antares are lesser, whiter stars of upper Scorpius.

Saturday, May 9

■ Summer is still six weeks away, but the Summer Triangle is beginning to make its appearance in the east, one star after another. The first in view is bright 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 by midnight.

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This Week's Planet Roundup

Mercury is still out of sight in conjunction with the Sun. But just wait. Later this month it will emerge into evening twilight view and pair up with Venus on May 21st.

Venus (magnitude –4.7, in north-central Taurus) is the bright white "Evening Star" in the west during and after dusk. It's still shining at its brightest.

Look upper right of Venus for Capella, about two fists at arm's length away. A bit farther to Venus's left is Betelgeuse.

Much closer above Venus is Beta Tauri (El Nath), fainter at magnitude 1.6. Venus creeps a little closer to Beta this week (from 3.3° to 1.6° ), then stalls out without quite reaching it. Next week Venus will start falling back away.

Meanwhile the whole scene is sinking lower. On May 1st Venus remains shining in the northwest for about 1½ hours after the end of twilight, but by the 8th it sets only about an hour after the last trace of daylight is gone.

In a telescope, meanwhile, Venus is growing more dramatic. This week its crescent enlarges from 39 to 44 arcseconds in diameter, while waning in phase from 24% to just 18% sunlit. It's on its way down to conjunction with the Sun on June 3rd.

Mars, Jupiter, and Saturn (magnitudes, +0.4, – 2.4, and +0.5, respectively) shine in the southeast before and during early dawn.

Jupiter, the brightest, is on the right. Before dawn begins, spot the Sagittarius Teapot to the right of it.

Saturn glows pale yellow 5° to Jupiter's left.

Mars is much farther to Saturn's lower left. It's moving away from the other two. On the morning of May 2nd Mars is 21° from Saturn; by the 9th it's 25° away.

Uranus is hidden behind the glare of the Sun.

Neptune, a mere 8th magnitude, is barely risen in the east 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, GMT, or Z time) minus 4 hours.

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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.

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, are the even larger Interstellarum atlas (stars to magnitude 9.5) and 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 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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Audio sky tour. Out under the evening sky with your earbuds in place, listen to Kelly Beatty's monthly podcast tour of the heavens above. It's free.