Sky at a Glance | May 16th, 2008

By: Alan MacRobert May 16, 2008 0

Some daily events in the changing sky for May 16 – 24.

In early dawn later this week, the waning Moon marches past the Sagittarius Teapot and Jupiter. The scene is plotted for the middle of North America. European observers: move each Moon symbol a quarter of the way to the one for the previous date.

Sky & Telescope diagram

Friday, May 16

Face south and look very high after dark this week for bright Arcturus, a yellow-orange giant. Look far to its lower right (by about three fist-widths at arm's length) for hotter but slightly dimmer Spica, pale blue-white.

Saturday, May 17

How low can you see to your north horizon? That's where you'll find W-shaped Cassiopeia around 10 or 11 p.m. this week. If you're far enough north, that is! From the latitudes of Atlanta, Houston, and San Diego, part of the Cassiopeia W will be below your horizon. From South Florida, the W goes below the horizon completely.

Sunday, May 18

Face southeast after dusk and look very high for bright Arcturus, 37 light-years away. Look low in the northeast for equally bright Vega, 25 light-years away. These are the two brightest stars of late spring and summer. Their nearness is part of the reason why; most naked-eye stars are typically 100 to more than 1,000 light-years distant.

Monday, May 19

Full Moon (exact at 10:11 p.m. EDT).

Getting there.... On the evening of May 18th, Doug Zubinel in Kansas caught Mars on its way toward Eta Cancri and the Beehive Cluster.

Doug Zubinel

This evening Mars skims just north of Eta Cancri, magnitude 5.3. They'll be less than 3 arcminutes apart during evening twilight in the Eastern time zone, from about 8:00 to 9:30 p.m. EDT. See the map and article in the May Sky & Telescope, page 72, or online.

Tuesday, May 20

The bright Moon shines low in the southeast this evening. Look above it for orange-red Antares and other stars of upper Scorpius.

The red long-period variable stars RS Librae and RS Scorpii should be at maximum light (7th or 8th magnitude) this week.

Wednesday, May 21

The sky right after nightfall is again moonless, so observers in the southernmost US, the tropics, and the Southern Hemisphere have a window of darkness to try for Comet Boattini. It has brightened more than expected to about 6th magnitude. This week it's crossing northern Pyxis. See our article and finder chart. And here are pictures and a light curve.

For skywatchers in Europe, Africa, and on the east coast of the Americas, Jupiter is without a visible moon for 18 minutes late tonight or early Thursday morning — a rare event. See our article.

Thursday, May 22

Saturn is at eastern quadrature, 90° east of the Sun.

Tonight Mars passes right between a pair of 6th-magnitude stars in the Beehive cluster, from about 11:30 to 12:30 p.m. Pacific Daylight Time. Even if Mars won't be in view for you that late, you can still use a telescope earlier in the evening to watch the planet slowly moving. See the map and article in the May Sky & Telescope, page 72, or online.

Friday, May 23

Mars skims even closer north of another Beehive star, this one magnitude 6.9, around 9 p.m. Eastern Daylight Time. They'll be only about 16 arcseconds apart when closest — about three Mars diameters. Use high power to see through the planet's glare.

Early risers Saturday morning will find Jupiter below the waning gibbous Moon in the south.

Saturday, May 24

A small telescope will always show Titan, Saturn's largest and wildest moon. Tonight Titan is four ring-lengths to Saturn's east. A guide to identifying all six of Saturn's satellites that are sometimes visible in amateur scopes is in the May Sky & Telescope, page 60.

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 foldout map in each issue of Sky & Telescope, the essential magazine of astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of maps; the standards are Sky Atlas 2000.0 or the smaller Pocket Sky Atlas) and good deep-sky guidebooks (such as Sky Atlas 2000.0 Companion by Strong and Sinnott, the even more detailed Night Sky Observer's Guide by Kepple and Sanner, or the classic Burnham's Celestial Handbook). Read how to use them effectively.

More beginners' tips: "How to Start Right in Astronomy".

This Week's Planet Roundup

To your eyeball, a telescope is doing well if it just shows Mercury's phase clearly. Centuries of astronomers couldn't distinguish surface markings reliably enough to find the planet's correct rotation period. But infrared imaging and video-frame stacking have brought Mercurian surface features in range of amateurs. Sean Walker used a 12.5-inch reflector in broad daylight to take these infrared images on May 5th, about an hour before sunset. The times are Universal Time.

S&T: Sean Walker

Mercury is still up in evening twilight, but it's fading fast now: from magnitude +0.6 on May 16th to +2.1 on the 24th. So look for it early in the week. It's fairly low in the west-northwest as twilight deepens. See article.

Venus is hidden in the glare of the Sun. It will stay there for months.

Mars (magnitude +1.4, in Cancer) shines high in the west after dark, off to the upper left of the Castor-and-Pollux couple. Each week Mars is moving farther away from them and closer to the Saturn-and-Regulus couple, still well off to Mars's upper left. They'll meet up for a close get-together in early July.

On the evenings of May 22nd and 23rd, Mars is right inside the Beehive star cluster. See the May Sky & Telescope, page 72.

Distant Mars was a minuscule 5.4 arcseconds wide when Sean Walker took this image on the evening of May 13th. Even so, it shows recognizable details: the dark-collared North Polar Cap at top, dark Syrtis Major through the cloud at the preceding (right) limb, and Sinus Sabaeus across lower center, ending at Sinus Meridiani near the terminator. This stacked-video image was taken with a 12.5-inch reflector.

S&T: Sean Walker

In a telescope, Mars is a minuscule 5.2 arcseconds wide — a very tiny blob.

Jupiter (magnitude –2.5, in eastern Sagittarius) rises around midnight daylight saving time, left of the Sagittarius Teapot. It's highest in the south before dawn. (The table of Jupiter's satellite phenomena in the May Sky & Telescope is incorrect; use this corrected version.)

Saturn glows high in the southwest after dark, just 2.4° from fainter Regulus (magnitude +1.4). They're quite the eye-catching couple. Each week now, they're gradually pulling a little farther apart.

Telescope users: can you see the pair of white storms on Saturn? How big a telescope do you need? To predict when they'll be turned into view (which happens at least twice a day), see the picture caption at the bottom of this page.

A white storm is visible in Saturn's South Temperate Zone — and since this picture was taken, it has divided into two! The original storm shows plainly in this stacked-video image taken by Sean Walker through a 12.5-inch reflector at 0:42 UT April 23rd during excellent seeing. "The white spot was visible in an eyepiece at over 500x, particularly through a green filter," Walker writes. North is up.

To find when the white spots are in view: For your date, look up Saturn's System II central-meridian longitude in this table (it's the "CMII" column). That's the value for 0:00 Universal Time (UT or GMT) that date. To this value, add 33.8° for each whole hour since 0:00 UT, and 0.56° for each minute, for the time you plan to observe. See what you get. Find a good Saturn-observing time and date for you that results in something around 75°, and plan to be out then with your scope.

P.S.: Here's an incredible closeup shot of the storm by Cassini taken on March 4th. Cassini's radio instruments find that the storm is full of lightning.

S&T: Sean Walker

This week Saturn is at eastern quadrature, 90° east of the Sun. So this is when its shadow is cast most sideways onto its rings. See our Saturn observing guide in the April Sky & Telescope, page 66.

Uranus and Neptune (magnitudes 6 and 8, respectively, in Aquarius and Capricornus) are in the east and southeast just before dawn.

Pluto (magnitude 14.0, in northwestern Sagittarius) is well up in the southeast after midnight. If you've got a big scope and ambition to match, use our article and finder chart.

All descriptions that relate to your horizon or zenith — 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 (UT, UTC, or GMT) minus 4 hours.

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About Alan MacRobert

Alan M. MacRobert became an avid Sky & Telescope subscriber in 1966 at age 14, joined the editorial staff in 1982, and is now a senior contributing editor, semi-retired. He played a role in practically every part of the magazine and the company's other products for more than a generation, both on the amateur-observing side and the science-reporting side. In 1994 a book collection of his observing how-tos and telescopic sky tours was published as Star Hopping for Backyard Astronomers. He has produced This Week's Sky at a Glance online every week since 1989.