Sky at a Glance | July 15th, 2011

By: Alan MacRobert July 15, 2011 0

Alpha and Beta Capricorni are 2.3° apart and fit easily into even a 15× field of view. Here they're oriented as they appear from mid-northern latitudes not long after they rise. Both are optical double stars. Alpha can often be split with the unaided eye, but Beta needs optical aid; its components appear closer together, and the fainter one is magnitude 6.0.

Akira Fujii

Friday, July 15

After the just-past-full Moon rises into good view late this evening, use binoculars to look a little above it for Beta Capricorni and, higher, the wide double star Alpha Capricorni. With good distance vision you can normally split Alpha Cap naked-eye. Can you still do this with the bright Moon so close?

Saturday, July 16

With summer almost a third of the way through, the Big Dipper is descending in the northwest after dark and starting to scoop to the right, dipper-wise, as if picking up water to dump over the world in the evening next spring. See the picture below.

Sunday, July 17

Titan, the brightest satellite of Saturn, can be found in a telescope about four ring-lengths east of Saturn this evening and tomorrow evening. With a 6-inch scope you can make out the orange tint of Titan's hydrocarbon-smogged atmosphere.

The Big Dipper high in the northwest is starting to dip.

Akira Fujii

Monday, July 18

Arcturus is the bright star shining high in the southwest these evenings, far above Saturn and Spica. Arcturus is a yellow-orange giant 37 light-years away and about 150 times as luminous as the Sun. Its pale ginger-ale color is plain to the unaided eye. Compare this to the icy blue-white of Vega overhead, equally bright.

Look far to the right of Arcturus, at roughly the same height, for the Big Dipper, oriented about as shown here.

Tuesday, July 19

Mercury is at greatest elongation this evening, 27° east of the Sun, low in the west-northwestern twilight.

Wednesday, July 20

Now's the time of year to work through the rich but low tail of Scorpius with a telescope right after dark. Explore a whole nest of little-known star clusters near M6, the Butterfly Cluster, with Sue French's Deep-Sky Wonders article and chart in the July Sky & Telescope, page 66.

When DAWN took this image of the asteroid Vesta on June 24th, it was the best image ever obtained of the odd minor planet. Vesta is about 510 km (315 miles) wide. Much better pix are coming as DAWN works its way down into a lower orbit.

NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

Thursday, July 21

The brightest asteroid, 4 Vesta, has brightened to magnitude 6.0 as it approaches opposition in Capricornus. It's easily visible in binoculars in late evening; use our online finder chart or look in the August 2011 issue of Sky & Telescope, page 53. The Dawn spacecraft has taken up orbit around Vesta and should be starting its science imaging around now!

Friday, July 22

Last-quarter Moon tonight (exact at 1:02 a.m. Eastern Daylight Time). The Moon rises around the middle of the night with Jupiter below it. By dawn they're very high in the southeast.

Saturday, July 23

Keep an eye out for occasional Delta Aquarid meteors coming out of the southeast late at night for the next month or so.

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).

Sky Atlas 2000.0 (the color Deluxe Edition is shown here) plots 81,312 stars to magnitude 8.5. That includes most of the stars that you can see in a good finderscope, and typically one or two stars that will fall within a 50× telescope's field of view wherever you point. About 2,700 deep-sky objects to hunt are plotted among the stars.

Alan MacRobert

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 (about magnitude +0.3) remains very low in the west-northwest in twilight, now becoming a little lower each day. Don't confuse it with Regulus to its upper left. Mercury and Regulus will pass 3° apart on July 26th.

Venus is hidden deep in the glow of sunrise.

Mars (magnitude +1.4, in Taurus) is moderately low in the east-northeast as dawn begins to brighten. Look for it very far lower left of bright Jupiter. To Mars's right or upper right is Aldebaran, similar in brightness and color. Farther to Mars's upper left is brighter Capella.

In a telescope Mars is still just a tiny blob only 4.3 arcseconds in diameter. It's on its way to a poor opposition (13.9 arcseconds wide) next March.

Jupiter on the morning of July 28th, imaged by S&T's Sean Walker. The South Equatorial Belt (above center) remains wide; the North Equatorial Belt remains narrow and darker red-brown. The black dot is the shadow of Io. Walker used a 12.5-inch Newtonian telescope and an Imaging Source camera in "fairly good" seeing.

S&T: Sean Walker

Jupiter (magnitude –2.3, in southern Aries) rises around 1 a.m. daylight saving time and shines high in the east-southeast by dawn. Look below it for the head of Cetus, rather dim.

Saturn (magnitude +0.9, in Virgo) is sinking lower in the west-southwest at dusk. Shining 14° left of it is similar, but bluer, Spica. About 1° to Saturn's right is fainter Porrima (Gamma Virginis).

Uranus (magnitude 5.9, in western Pisces) and Neptune (magnitude 7.9, in western Aquarius) are up in good view during the early-morning hours. Here's our printable finder chart for them both.

Pluto (magnitude 14.0, in northern Sagittarius) is highest in the south around 11 or midnight. A big finder chart for it is in the July Sky & Telescope, page 64.

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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