Sky at a Glance | July 27th, 2012

By: Alan MacRobert July 27, 2012 0

All week, watch Mars move in on Saturn and Spica at dusk.

Friday, July 27

Mars has crept to within 11° of Saturn and Spica, on its way to passing between them in mid-August.

Look left of the Moon this evening (by a fist-width at arm's length or more) for the orange-red supergiant star Antares. Closer left of the Moon are the three fainter stars that mark the head of Scorpius, lined up about vertically.

Before or during dawn Saturday morning, telescope users near North America's West Coast can see Jupiter's satellites Io and Europa both casting their tiny black shadows onto Jupiter's face from 4:45 to 5:33 a.m. Pacific Daylight Time.

Saturday, July 28

Fiery Antares shines lower right of the waxing gibbous Moon tonight.

Sunday, July 29

Before and during dawn Monday morning, Jupiter is closest to Aldebaran. They're 4.7° apart, with Aldebaran to Jupiter's lower right.

Monday, July 30

The waxing gibbous Moon this evening hangs over the handle of the Sagittarius Teapot.

Tuesday, July 31

During early dawn Wednesday and Thursday mornings, look low in the east to spot brilliant Venus, magnitude –4.6. Look 2° upper left of it (roughly a finger's width at arm's length) for Zeta Tauri, magnitude 3.0. That's a brightness difference of just over 1,000 times! Binoculars will be necessary as dawn brightens.

Wednesday, August 1

Full Moon tonight (exact at 11:27 p.m. EDT). The Moon is in dim Capricornus. Shining high above it is Altair.

Thursday, August 2

Arcturus is the brightest star in the west after dark at this time of year. It and Vega, almost overhead, are the two leading stars of summer. Look off to the right of Arcturus, in the northwest, to spot the Big Dipper dipping down.

Friday, August 3

As summer enters its second half, the Summer Triangle approaches its greatest height in the evening. Face east and look almost straight up after nightfall. The brightest star there is Vega. Toward the northeast from Vega (by two or three fist-widths at arm's length) is Deneb. Toward the southeast from Vega by a greater distance is Altair.

Saturday, August 4

The waning gibbous Moon rises in the east as twilight fades into night. Look left or upper left of it for the Great Square of Pegasus, balancing on one corner.

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'll need a detailed, large-scale sky atlas (set of charts). The standards are the little Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and the even larger 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 Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the classic if dated Burnham's Celestial Handbook.

Can a computerized telescope replace charts? I don't think so — not for beginners, anyway, and especially not on mounts and tripods that are less than top-quality mechanically (able to point with better than 0.2° repeatability). As Terence Dickinson and Alan Dyer say in their invaluable 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

Bright Jupiter and brighter Venus are pulling away from each other in the eastern sky at dawn.

Sky & Telescope diagram

Mercury is out of sight in conjunction with the Sun.

Venus and Jupiter (magnitudes –4.6 and –2.2) shine dramatically in the east before and during dawn, as shown at right. They've widened to about 14° apart now, with Jupiter higher. Look for Aldebaran, much fainter, lower right of Jupiter. Also near Jupiter are the Hyades, and higher above are the Pleiades.

The asteroids Ceres and Vesta, magnitudes 9.1 and 8.4, are in the area too! See article and finder charts: Ceres and Vesta, July 2012 – April 2013.

Mars and Saturn (magnitudes +1.1 and +0.8, respectively) are low in the west-southwest at dusk. Saturn stands 4½° above similarly-bright Spica. Mars is approaching closer to them every day and will pass between them on August 13th and 14th.

Uranus (magnitude 5.8, at the Pisces-Cetus border) and Neptune (magnitude 7.8, in Aquarius) are high in the southern sky before the first light of dawn. Finder charts for Uranus and Neptune.

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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