Sky at a Glance | May 13th, 2011

By: Alan MacRobert May 13, 2011 0

The waxing gibbous Moon passing under Saturn and Spica.

Friday, May 13

Look for Saturn glowing with a steady light well to the upper left of the Moon this evening with Porrima next to it, as shown here.

As dawn brightens this week, look very low in the east for Venus, Jupiter, Mercury, and faint Mars. Bring binoculars; you'll probably need them for Mercury, and Mars is impossible without them (and sometimes even with them).

See the May 15th scene below. For a view of the planets' changing positions every morning this month, see our article and animation. You can pause the animation at any date.

Saturday, May 14

Now it's Spica's turn to shine upper left of the Moon in the evening.

Mercury has brightened in the last week to form a fine triangle with Venus and Jupiter in the dawn, but Mars remains (probably) a binocular object at best.

Sky & Telescope diagram

Sunday, May 15

As night descends, look west-northwest for Pollux and Castor lined up almost horizontally. They're separated by about three finger-widths at arm's length. Far to their lower left is Procyon. Farther to their lower right is brighter Capella.

The asteroid 10 Hygiea is at opposition this week, at magnitude 9.2 in southern Libra. Hygiea is the fourth-largest asteroid; it appears as dim as it does because its surface is quite black. See the finder chart and article in the May Sky & Telescope, page 56.

Monday, May 16

Face northwest this evening and look high for the Big Dipper, now hanging down by its handle. Just a few weeks ago it was horizontal! That sort of quick change happens to star patterns passing near the zenith. (Can you can figure out why? Answer next week.)

Tuesday, May 17

Full Moon (exact at 7:09 a.m. Eastern Daylight Time). Look for Antares below the Moon this evening.

Wednesday, May 18

The three brightest stars in the spring evening sky are Arcturus, now high in the southeast, Vega lower in the northeast, and Capella in the northwest. All are zero magnitude. Vega and Capella are at exactly the same height sometime around 9:30 or 10 p.m. daylight saving time, depending on your location. How accurately can you time this event for where you live?

Thursday, May 19

This is the time of year when Cassiopeia sits at its lowest due north after dark, looking like a wide W rather than a flattened M. How low it appears depends on your latitude. If you're as far south as Florida, Cassiopeia is completely out of sight below the north horizon.

Now that Jupiter is higher and easier to see, you can use it as a guide to locating the other three dawn planets.

These scenes are always drawn for 40° north latitude. If you're south of there, the view will be rotated counterclockwise by roughly your difference from 40° latitude. (The visibility of objects in bright twilight is exaggerated.)

Sky & Telescope diagram

Friday, May 20

As dawn brightens early Friday, Saturday, and Sunday mornings, Venus forms a right triangle a little more than 2° wide with Mercury below it and faint Mars to its left. Look low in the east, using binoculars.

Saturday, May 21

Arcturus is the brightest star very high in the southeast after dark. Vega, equally bright, is much lower in the northeast. A third of the way from Arcturus to Vega look for the dim semicircle of Corona Borealis, the Northern Crown, with its one moderately bright star, Alphecca. Two-thirds of the way from Arcturus to Vega is the dim Keystone of Hercules.

Want to become a better amateur astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

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 magazine of astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but that's less than one star in an entire telescopic field of view, on average. By comparison, Sky Atlas 2000.0 plots 81,312 stars to magnitude 8.5, typically one or two stars per telescopic field. Both atlases include many hundreds of deep-sky targets — galaxies, star clusters, and nebulae — to hunt among the stars.

Sky & Telescope

Once you get a telescope, to put it to good use you must have a detailed, large-scale sky atlas (set of charts). The standards are the Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger Sky Atlas 2000.0 (stars to magnitude 8.5); and the even larger and deeper Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts effectively.

You'll also want a good deep-sky guidebook, such as Sky Atlas 2000.0 Companion by Strong and Sinnott, or the more detailed and descriptive Night Sky Observer's Guide by Kepple and Sanner, or the classic if dated Burnham's Celestial Handbook.

Can a computerized telescope take their place? I don't think so — not for beginners, anyway, and especially not on mounts that are less than top-quality mechanically. 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

Mercury, Venus, Mars, and Jupiter continue their evolutions low in the bright glow of dawn. Use binoculars 30 minutes before sunrise; look low in the east. Venus is the brightest. Second-brightest is Jupiter, now moving farther to Venus's upper right. Below Venus by about 1 ½° is Mercury, still brightening. Faint little Mars is a real challenge object to their left or lower left.

See our article "The Four-Planet Dance of 2011" about the whole month of this dawn parade, with daily panels in an animation. You can pause the animation at your date of choice.

Saturn's white spot continues re-erupting! The head of the pale streamer wrapping around the planet has rebrightened with new upwelling material, as seen in this image taken by Christopher Go on May 12th (at 13:32 UT; System III central-meridian longitude 314Â°). "The old and new materials are interacting, forming bright and complex features," he writes. South here is up.

Also see his gif animation or wmv animation of several more images taken over the course of 84 minutes, confirming dark spoke markings on the celestial east (following) side of the bright B ring. In the animations, north is up.

Christopher Go

Saturn (magnitude +0.6, in Virgo) is the only planet in good telescopic view. Look for it high in the south-southeast as the stars come out, with Spica to its lower left and bright Arcturus nearly twice as far to its left. Saturn is highest in the south not long after dark.

In a telescope Saturn's rings are 7.6° from edge on, nearly their minimum tilt for this year and for more than a decade to come. The rings are casting a relatively wide, prominent black shadow southward onto the globe, and the globe's shadow on the rings is visible just off the globe's celestial east (following) side. Saturn's months-old white streak is still active, as seen here. See how many of Saturn's satellites you can identify in your scope using our Saturn's Moons tracker.

Saturn has now closed to about 3/4° from fainter Gamma Virginis (Porrima). This star is an attraction in its own right: a fine, close telescopic binary with a current separation of 1.7 arcseconds. Use high power and hope for good seeing. See the article in the April Sky & Telescope, page 56. Saturn will pass 0.4° from Gamma Vir in mid-June.

Uranus (magnitude 5.9, in western Pisces) is very low in the east just before the first light of dawn.

Neptune (magnitude 7.9, in Aquarius) is in the southeast just before 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) equals Universal Time (also known as UT, UTC, or GMT) minus 4 hours.

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