Friday, January 20 Jupiter's moon Io crosses Jupiter's face from 8:07 to 10:17 p.m. EST. Io's tiny black shadow follows behind from 9:28 to 11:37 p.m. EST.
Watch the waxing Moon climb up past Venus later this week. (This scene is 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 blue 10° scale is about the size of your fist held at arm's length. The Moon is shown three times actual size.)
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.
Sunday, January 22 Bright Orion stands upright at its highest in the south around 8 or 9 p.m. this week. Orion's top left corner is fire-colored Betelgeuse, one of the stars of the equilateral Winter Triangle. The other two are Procyon, about two fist-widths at arm's length lower left of Betelgeuse, and bright Sirius, a similar distance below Betelgeuse. Algol in Perseus is at minimum light, magnitude 2.4 instead of its usual 2.1, for about two hours centered on 9:05 p.m. EST (6:05 p.m. PST). New Moon (exact at 2:39 a.m. Monday morning EST).
Monday, January 23 By 9 p.m. the Big Dipper is already standing vertically on its handle, well up in the northeast an early sign of the approach of spring. Jupiter's Great Red Spot crosses the planet's central meridian around 7:54 p.m. EST. How well do you know the telescopic sights of Orion's Belt and Sword, really? Make new finds here with Sue French's Deep-Sky Wonders article and chart in the January Sky & Telescope, page 54.
Tuesday, January 24 In twilight, look far lower right of Venus for the thin crescent Moon, as shown above.
Wednesday, January 25 Venus and the waxing crescent Moon shine in the west-southwest in twilight about 8° apart, as shown above.
Thursday, January 26 The Moon shines over Venus in twilight, as shown above.
Friday, January 27 Now the Moon is higher above Venus. Once the stars come out, look a similar distance to the Moon's right for the bottom star of the Great Square of Pegasus. The Great Square is balancing on this corner.
Saturday, January 28 This evening, look right of the Moon for a different corner of the Great Square of Pegasus: its leftmost corner. About twice as far to the Moon's upper left, Jupiter is shining brightly.
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).
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.
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.
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
Mercury is hidden in the glare of the Sun.
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.
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 still a small gibbous disk, 14.5 arcseconds in diameter.
Mars (about magnitude 0.5, at the Leo-Virgo border) rises in the east around 9 p.m., far beneath Regulus and the Sickle of Leo. Mars is brightening rapidly now as it approaches Earth. It shines highest in the south, in best telescopic view, around 3 or 4 a.m. Mars has grown to 11½ arcseconds wide, on its way to 13.9″ when closest to Earth in early March.
Jupiter (magnitude 2.5, still at the Aries-Pisces border) shines highest in the south in early twilight, moves lower toward the southwest as evening advances, and sets in the west around midnight or 1 a.m. In a telescope Jupiter has shrunk to 40 arcseconds wide.
Saturn (magnitude +0.6, in Virgo) rises in the east around midnight and is high in the south in early dawn. Spica, a bit fainter at magnitude +1.0, is 7° to its right or upper right. Saturn's rings are now tilted a generous 15° from our line of sight.
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.
Uranus (magnitude 5.9, near the Circlet of Pisces) is in the southwest right after dark.
Neptune (magnitude 7.9, at the Aquarius-Capricornus border) is disappearing into the glow of evening twilight.
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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