Sky at a Glance | October 19th, 2012

By: Alan MacRobert October 19, 2012 0

The 4-day-old Moon is obvious, Mars and Antares much less so.

Friday, October 19

The crescent Moon shines in the southwest as twilight fades. If it were a bow, it would be shooting an arrow to the lower right above the Mars-and-Antares pair, as shown here. Binoculars will help you pick out the two similar-looking, orange-red points.

The annual Orionid meteor shower should be getting under way in the hours before dawn Saturday morning, and it should continue in the early-morning hours for the next few days. You may see 10 or 20 Orionids per hour. The shower's radiant point is at the top of Orion's Club, which doesn't rise high until after well midnight. There will be no moonlight for the next few mornings.

At 10:48 p.m. Eastern Daylight Time, Jupiter's moon Io reappears out from behind Jupiter's eastern limb. Later, Jupiter's Great Red Spot crosses the planet's central meridian around 1:18 a.m. Saturday morning EDT (10:18 p.m. Friday evening PDT).

For all of Jupiter's satellite events and Great Red Spot transits this month, good worldwide, see "Action at Jupiter" in the October Sky & Telescope, page 52.

Saturday, October 20

As twilight fades this evening, Mars and Antares are at their minimum separation of 3½°. Look for them quite low in the southwest, as shown above.

Sunday, October 21

First-quarter Moon (exact at 11:32 p.m. EDT). The Moon shines in the south to southwest during evening. Look for Altair high above it as the stars come out. Later in the evening, Altair is upper right of the Moon.

Monday, October 22

Vega is the brightest star high in the west these evenings. Even higher above it is Deneb. Farther off to Vega's left or lower left is the third Summer Triangle star, Altair.

Tuesday, October 23

Wintry Orion sparkles above the east-southeast horizon as early as 11 p.m. now, depending on your location. Earlier in the evening, keep watch for Orion rising below or lower right of brilliant Jupiter.

Wednesday, October 24

Around 8 or 9 p.m. the Big Dipper lies low and level above the north-northwest horizon. The farther north you live, the higher it will appear. If you're as far south as Miami, it's below the horizon completely.

Thursday, October 25

The W pattern of Cassiopeia is tipping nearly vertically high in the northeast after dusk. It stands exactly vertical around 9 p.m., depending on your location. The W's brightest side is on top.

Friday, October 26

The Ghost of Summer Suns. Halloween is approaching, and this means that Arcturus, the star sparkling low in the west-northwest in twilight, is taking on its role as "the Ghost of Summer Suns." What does this mean? For several days centered on October 29th every year, Arcturus occupies a special place above your local landscape. It closely marks the spot in your sky where the Sun stood at the same time, by the clock, during warm June and July — in broad daylight, of course. So, in the last days of October each year, you can think of Arcturus as the chilly Halloween ghost of the departed summer Sun.

The waxing gibbous Moon shines in the east early this evening. Look to its upper left for the Great Square of Pegasus, tipped onto one corner.

Saturday, October 27

The bright Moon shines below the Great Square of Pegasus's bottom corner early this evening. From the Square's left corner extends a big, slightly downward line of three stars (including the corner). These form the backbone and leg of Andromeda.

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 guide to 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'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 with a telescope 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? Not for beginners, I don't think, and certainly 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

Jupiter on October 23rd, showing its side away from the Great Red Spot. Below center, the North Tropical Zone has turned fully white again to separate the tan North Equatorial Belt (NEB) from the narrower North Temperate Belt (NTB) below it. Note the dark, sharp, scalloped northern rim of the NTB, and the row of three bright white outbreaks in the NEB. Jim Phillips in South Carolina used a 10-inch Maksutov scope to take this stacked-video image at 5:31 UT. South is up.

Jim Phillips

Mercury (magnitude –0.2) is having a poor evening apparition. Using binoculars, look for it 20 or 30 minutes after sundown very low in the southwest, to the lower right of Mars and Antares.

Venus (magnitude –4.0, at the Leo-Virgo border) rises in darkness more than an hour before the first glimmer of dawn. By dawn it's shining brightly in the east.

Mars (magnitude +1.2, in Ophiuchus) is still low in the southwest in evening twilight. It's more or less above similar-looking Antares. The two are about 4° or 5° apart.

Jupiter (magnitude –2.7, in Taurus) rises in the east-northeast around 8 or 9 p.m. daylight saving time. Once it's clear of the horizon, look for fainter orange Aldebaran to its right and Beta Tauri (Elnath) a little farther to its left. By dawn this lineup-of-three stands high and vertical in the west.

Saturn is hidden behind the glare of the Sun.

Uranus (magnitude 5.7, at the Pisces-Cetus border) and Neptune (magnitude 7.9, in Aquarius) are in in good view in the southeast to south during evening. 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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