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
- As twilight begins to fade, the crescent Moon shines in the southwest. If the crescent were a bow, it would be shooting an arrow toward Mercury far to its lower right.
Saturday, January 12
- The bright variable star Algol (almost behind dim Comet Holmes!) should be at the bottom of one of its eclipses, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 9:31 p.m. Eastern Standard Time. Algol takes several additional hours to fade and to rebrighten. (For all times of Algol's minima this month, good worldwide, see the January Sky & Telescope, page 78.)
Sunday, January 13
- In the eastern evening sky this week, brilliant Mars continues to shine near the center of a huge, lopsided rectangle of bright stars. These are: Capella far to Mars's upper left, orange Aldebaran far to Mars's upper right, orange Betelgeuse (in Orion's shoulder) far to Mars's lower right, and the Castor-and-Pollux pair even farther to Mars's lower left. The eye-catching star much closer above Mars is Beta Tauri (El Nath), magnitude 1.6.
The Moon crosses this rectangle later in the week, as shown in the illustration below.
Monday, January 14
- Look for the Great Square of Pegasus, balanced on one corner, to the right of the Moon this evening. The neck and head stars of Pegasus extend down from the Great Square's bottom corner at this time of year. The main stars of Andromeda extend up from its top corner. After dinnertime, this whole arrangement stretches nearly from the horizon to the zenith!
Tuesday, January 15
- First-quarter Moon (exact at 2:46 p.m. EST).
- Algol should be at minimum for a couple hours centered on 6:21 p.m. EST. Watch it rebrighten during the following hours.
Wednesday, January 16
- Brilliant Sirius rises in the east-southeast (below Orion) during late twilight. When will you first see it? Each evening it rises four minutes earlier. Being so bright, Sirius often twinkles in vivid colors when it's low — as hand-held binoculars show especially clearly.
Thursday, January 17
- The waxing gibbous Moon skims the northern fringe of the Pleiades around 1:30 to 4:30 a.m. EST Friday morning for skywatchers in North America. Occultation predictions for the northern U.S. and Canada.
Friday, January 18
- A small telescope will always show Titan, Saturn's largest moon. This evening it's is four ring-lengths to Saturn's east. A 6-inch telescope will begin to show the orange color of its atmospheric smog. A guide to identifying all six of Saturn's satellites visible in amateur scopes is in the January Sky & Telescope, page 66.
Saturday, January 19
- Mars shines very close to the gibbous Moon early this evening as seen from North America, as shown below, and around the middle of the night as seen from Europe.
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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