Some daily events in the changing sky for January 11 19.
Comets Holmes and Tuttle remain in the evening sky, though moonlight has returned. Use binoculars for both. Holmes continues spreading out ever bigger and dimmer, so the moonlight will affect it particularly badly. Holmes is getting close to Algol and crosses right over it for a few days around the 21st; see chart. (The dates on the chart are for 0:00 Universal Time, which falls on the evening of the previous date in the time zones of the Americas.)
Tuttle is much smaller than Holmes, greener, more concentrated, and about magnitude 6.0. It's now crossing southern Cetus. See the article and chart in the January Sky & Telescope, page 73, or the brief version online. (Again, dates on the chart are for 0:00 UT.)
Tuttle a contact binary? Astronomers have used the Arecibo planetary radar to get an image of Comet Tuttle's solid nucleus with 300-meter resolution. J. K. Harmon and colleagues find that the nucleus "is a strongly bifurcated object, possibly a contact binary, with two roughly spherical lobes measuring 3 and 4 km in diameter (+/- 25 percent)," according to IAU Circular #8909. Also, "following the changing rotation aspect from night to night and within the 2.5-hour observing sessions gives a preliminary estimate of 7.7 +/- 0.2 hours for the rotation period."
Friday, January 11
Saturday, January 12
Sunday, January 13
The Moon crosses this rectangle later in the week, as shown in the illustration below.
Monday, January 14
Tuesday, January 15
Wednesday, January 16
Thursday, January 17
Friday, January 18
Saturday, January 19
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 foldout map in 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 maps; the standard is Sky Atlas 2000.0) and good deep-sky guidebooks (such as Sky Atlas 2000.0 Companion by Strong and Sinnott, the even more detailed Night Sky Observer's Guide by Kepple and Sanner, or the enchanting though increasingly dated Burnham's Celestial Handbook). Read how to use them effectively.
More beginners' tips: "How to Start Right in Astronomy".
This Week's Planet Roundup
Mercury (magnitude 0.8) is emerging into a good evening apparition low in the sunset. Look for it above the west-southwest horizon about 40 minutes after sundown. It's on its way up into best view next week.
Venus (magnitude 3.9, in southern Ophiuchus) is the bright "Morning Star" low in the southeast before and during dawn, as shown here. Look for much dimmer Antares sparkling orange-red well off to its right, and Jupiter down to its lower left.
Mars is three weeks past opposition, shining bright yellow-orange (about magnitude 1.1) in the east to southeast after dark (in northeastern Taurus). Mars is highest toward the south around 10 p.m. passing near the zenith for observers at mid-northern latitudes. It diminishes from 14.5 to 13.3 arcseconds in apparent size this week, falling behind us as Earth moves ahead in our faster orbit around the Sun. Mars is also becoming gibbous again. See the telescopic observing guide and surface-feature map in the November Sky & Telescope, page 66. A short version is online.
Jupiter (magnitude 1.8) is deep in the glow of dawn, far lower left of brighter Venus, as shown above. Look for it about 45 minutes before sunrise. (To find your local sunrise time, make sure you've put your location into our online almanac, and make sure the Daylight Saving Time box is unchecked.)
Once you've found Jupiter, watch it get higher and easier each morning as it closes in on Venus. On January 12th they're still 20° apart, but the gap between them is narrowing by 1° per day. These two brightest planets are heading toward a close conjunction (0.6° apart) on the morning of February 1st.
Saturn (magnitude +0.5, in Leo) rises in the east around 8 or 9 p.m. and is highest in the south in the early-morning hours. Fainter Regulus (magnitude +1.4) is 8° west of Saturn: to its upper right during late evening. Only a little dimmer than Regulus is Gamma Leonis (magnitude +2.1), 8° to Regulus's north. The three make an eye-catching triangle.
Neptune is lost in the sunset.
All descriptions that relate to your horizon or zenith including the words up, down, right, and left are written for the world's midnorthern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America. Eastern Standard Time (EST) equals Universal Time (UT, UTC, or GMT) minus 5 hours.
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