Sky at a Glance | January 13th, 2012

By: Alan MacRobert January 13, 2012 0

As dawn begins, Mars and Saturn are high and awaiting your telescope. For a few mornings this week the waning Moon passes below them.

Sky & Telescope diagram

Friday, January 13

Before and during dawn Saturday morning, Mars shines above the waning Moon, as shown at right.

Saturday, January 14

The tight telescopic double star Gamma (γ) Virginis shines above the waning Moon before and during dawn Sunday morning, as shown at right. Brighter Mars glows to the star's right.

Sunday, January 15

The sky's biggest asterism (informal star pattern) is the Winter Hexagon or Winter Circle. It fills the sky toward the east and south these evenings. Start with brilliant Sirius at its bottom. Going clockwise from there, march through Procyon, Pollux and Castor, Capella high up, Aldebaran over to Capella's right, down to Rigel, and back to Sirius.

Last-quarter Moon late tonight (exact at 4:08 a.m. on the 16th EST). The Moon rises around midnight local time tonight, with Spica a little above it and Saturn farther to its left.

Monday, January 16

How well do you know the telescopic sights of Orion's Belt and Sword, really? Make new finds with Sue French's Deep-Sky Wonders article and chart in the January Sky & Telescope, page 54.

Tuesday, January 17

Have you ever seen the Crab Nebula in a telescope? How about binoculars? This diffuse little glow is near the dimmer of Taurus's two horn tips. At magnitude 8.4 it needs a dark sky if you're using a small instrument — but give it a try with Gary Seronik's Binocular Highlight article and chart in the January Sky & Telescope, page 45.

Look southeast in early dawn, and you can watch the waning Moon cross upper Scorpius. (These scenes are drawn for the middle of North America. For clarity, the Moon is shown three times actual size.)

Sky & Telescope diagram

Wednesday, January 18

As dawn begins to brighten Thursday morning, look southeast for the waning crescent Moon with Antares to its lower right — an early preview of a landmark star of summer evenings.

Early on the morning of the 19th, the faint asteroid 911 Agamemnon will occult an 8.0-magnitude star in Lynx for up to 9 seconds along a track from the Washington DC area across most of the Great Lakes and into western Canada. Maps and details.

Thursday, January 19

Algol is at minimum brightness for about two hours centered on 9:15 p.m. Pacific Standard Time (12:15 on the 20th Eastern Standard Time).

Friday, January 20

Jupiter's moon Io crosses Jupiter's face from 8:07 to 10:17 p.m. EST, followed by its tiny shadow from 9:28 to 11:37 p.m. EST.

Saturday, January 21

Bright Capella passes closest to your zenith around 9 or 10 tonight, depending on how far east or west you are in your time zone. How accurately can you time when this happens, just by looking? Capella crosses right through your zenith if you're at north latitude 46° (Oregon, Montreal, central France).

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).

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 effectively.

You'll also want a good deep-sky guidebook, such as Sue French's new 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 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

Mars had grown to 9.0 arcseconds in diameter by January 1st, when Jim Phillips took this image with a 10-inch apo refractor and a Skynyx color video camera. The central-meridian longitude was 246°. South is up. The big dark prong at upper right is Syrtis Major. Note the white cloud haze on the right (morning) limb, and the patch of cloud near the evening terminator in Elysium next to dark Hyblaeus, lower left of center.

Jim Phillips

Mercury is hidden deep in the glow of sunrise.

Venus (magnitude –4.0, in Aquarius) is the brilliant “Evening Star” shining in the southwest during and after dusk. It will continue to move a little higher each week all winter.

In a telescope Venus is a small gibbous disk 14 arcseconds in diameter; it's still on the far side of the Sun but rounding our way.

Mars (magnitude –0.1, at the Leo-Virgo border) rises in the east around 9 or 10 p.m., far beneath Regulus and the Sickle of Leo. Mars is brightening rapidly as it approaches Earth. It shines highest in the south around 3 or 4 a.m. In a telescope Mars has grown to 10 arcseconds wide, on its way to 13.9″ when closest to Earth in early March.

Jupiter is appearing smaller as Earth swings farther ahead of it in our faster orbit around the Sun. Christopher Go took this shot on January 18th at 11:20 UT, when large, dark Ganymede had recently left the planet's face and smaller, brighter Io was just about to. South is up, and the central-meridian longitude is 10°.

Writes Go, "The South Equatorial Belt is still very dark and active, while the North Equatorial Belt is very narrow now!" Note the thin, very long dark barge in the North North Temperate Belt.

Christopher Go

Jupiter (magnitude –2.5, at the Aries-Pisces border) shines highest in the south at dusk, moves lower toward the southwest as evening advances, and sets in the west around 1 a.m. In a telescope Jupiter has shrunk to 41 arcseconds wide.

Saturn (magnitude +0.6, in Virgo) rises in the east around 1 a.m. and is high in the south at dawn. Spica, just a bit fainter at magnitude +1.0, is 6° or 7° to Saturn's right or upper right. In a telescope, Saturn's rings are now presented to us a good 15° from edge on.

Uranus (magnitude 5.9, near the Circlet of Pisces) is still high in the southwest right after dark.

Neptune (magnitude 7.9, at the Aquarius-Capricornus border) is low in the west-southwest after dark.

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 Standard Time (EST) equals Universal Time (also known as UT, UTC, or GMT) minus 5 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.