Sky at a Glance | July 29th, 2011

By: Alan MacRobert July 29, 2011 0

Friday, July 29

Look southeast after dark, a little more than halfway from the horizon to straight overhead, for the bright star Altair. It's the eye of Aquila, the Eagle. At its distance of 17 light-years, Altair is one of our closest stellar neighbors. It's a fast-spinner, so much so that it's strongly elliptical rather than round — not that you can see any sign of this with any ordinary instrument!

Saturday, July 30

Now that summer is far advanced, the glowing band of the Milky Way forms a vast arch high across the sky after darkness is complete — if you're one of the few lucky people not living under light pollution. The Milky Way runs from Perseus and Cassiopeia low in the north-northeast, up and across the big Summer Triangle very high in the east, and down to Sagittarius and Scorpius low in the south. How much of it can you see?

New Moon (exact at 2:40 p.m. Eastern Daylight Time).

The tick marks show Vesta's location at 0:00 Universal Time on the dates indicated. It's moving toward the lower right in August. This is a narrow closeup; click for our larger, printable finder charts for Ceres and Vesta for 2011.

Sky & Telescope diagram

Sunday, July 31

The brightest asteroid, 4 Vesta, is at opposition this week, shining at magnitude 5.6 in Capricornus. It's an easy find in binoculars in late evening and can be seen with the unaided eye from a dark site. Use the finder chart in the August Sky & Telescope, page 53, or our Vesta and Ceres finder charts online. The Dawn spacecraft is now orbiting Vesta, taking pictures and gradually working its way down to a much lower orbit, which it will reach in early 2012.

Monday, August 1

As August begins, bright Vega crosses nearest the zenith around 11:00 p.m., depending on where you're located east-west in your time zone. How accurately can you time when this event happens for you? Vega goes exactly through the zenith if you're at latitude 39° north.

Tuesday, August 2

Before the waxing Moon starts lighting the evening sky in a few days, try hunting faint galaxies on the arched back of Draco using Ken Hewitt-White's "Going Deep" article and charts in the August Sky & Telescope, page 62.

The waxing Moon reappears at dusk this week below Saturn and Spica. (These scenes are drawn for the middle of North America. European observers: move each Moon symbol a quarter of the way toward the one for the previous date. The Moon is shown three times its actual apparent size. The blue 10° scale is about the size of your fist held at arm's length.)

Sky & Telescope diagram

Wednesday, August 3

The waxing crescent Moon is below Saturn at dusk, as shown above.

Thursday, August 4

This evening the Moon is below Spica at nightfall, as shown above.

Friday, August 5

The Moon lines up left of Spica and Saturn at dusk.

Mars, low in the east-northeast just before the first light of dawn, is passing less than 1° south (lower right) of the star cluster M35 in Gemini on Saturday and Sunday mornings. Use binoculars or a telescope.

Saturday, August 6

First-quarter Moon (exact at 7:08 a.m. EDT). The Moon is in the middle of Libra, to the right of upper Scorpius.

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 and Venus are hidden in the glare of the Sun.

Mars (magnitude +1.4, crossing from Taurus into Gemini) glows dim and distant low in the east-northeast before and during dawn. It's lower right of Capella and lower left of Aldebaran. In a telescope, Mars is just a tiny blob only 4.4 arcseconds in diameter. It's on its way to a poor opposition (13.9 arcseconds wide) next March.

Jupiter on the morning of July 31st, with Callisto passing south of it, imaged by S&T's Sean Walker. The South Equatorial Belt (above center) remains wide, and the great Red Spot lacks its usual light Red Spot Hollow. The North Equatorial Belt remains narrow and darker red-brown. Walker used a 12.5-inch Newtonian telescope and an Imaging Source video camera to create this stacked-frame image.

S&T: Sean Walker

Jupiter (magnitude –2.4, in southern Aries) rises in the east around midnight daylight saving time. Look above it for the little star pattern of Aries and (once Jupiter is well up) closer below it for the head of Cetus, rather dim. By dawn Jupiter shines very high in the southeast.

Saturn (magnitude +0.9, in Virgo) is sinking ever lower in the west-southwest at dusk. Look 12° left of it for Spica and 2° right or lower right of it for fainter Gamma Virginis (Porrima).

Uranus (magnitude 5.8, in western Pisces) and Neptune (magnitude 7.8, in western Aquarius) are well up in the east or southeast after midnight. Here's our printable finder chart for both.

Pluto (magnitude 14.0, in northern Sagittarius) is highest in the south soon after dark. 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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