Monday, January 16
• Mars continues to put on a nice show these January evenings. It appears to the upper left of Venus and some 30° above the southwestern horizon once twilight fades to darkness. The magnitude 1.0 Red Planet currently lies among the background stars of Aquarius, though it will cross into Pisces later this week. A telescope shows the world’s 5"-diameter disk, but you likely won’t see any surface detail.
Tuesday, January 17
• Asteroid 4 Vesta reaches opposition and peak visibility tonight. The brightest minor planet of 2017 shines at magnitude 6.2. That’s barely bright enough to see with the naked eye from under a dark sky, though binoculars make the task much easier. To find Vesta, start at magnitude 1.6 Castor in northern Gemini and draw a line to magnitude 1.2 Pollux. Continue that line to the south-southeast about twice the distance between the two stars until you land on 6th-magnitude Mu (m) Cancri. Vesta lies 2.2° northwest of Mu this evening.
Wednesday, January 18
• Jupiter dominates the morning sky in January. The giant planet resides in central Virgo, rising just before midnight local time and climbing halfway to the zenith in the southern sky by the time twilight begins. Jupiter shines brilliantly at magnitude –2.1 and shows a disk that spans 37" when viewed through a telescope. A small scope also reveals the planet’s four bright moons, though you may have to hunt for one of them this morning. The shadow of Europa starts to transit Jupiter at 1:12 a.m. EST and takes 2.5 hours to complete its journey across the cloud tops. The shadow lifts back into space at 3:42 a.m., just one minute after the moon itself begins a transit on the planet’s opposite limb. Also keep an eye on Jupiter when it rises late this evening in the company of a waning gibbous Moon. The two lie just 3° apart.
Thursday, January 19
• Last Quarter Moon occurs at 5:13 p.m. EST. The Moon doesn’t rise until nearly 1 a.m. local time tomorrow morning, however, by which time it will appear slightly less than half-lit. The Moon spends the morning hours on the border between Virgo and Libra.
• Mercury reaches the peak of its current apparition this morning. The innermost planet lies 24° west of the Sun at 5 a.m. EST and appears 10° above the southeastern horizon 30 minutes before sunrise. Shining at magnitude –0.2, it shows up nicely through the twilight glow. (If you don’t spot it right away, binoculars will bring it into view.) A telescope reveals Mercury’s 7"-diameter disk, which appears slightly more than half-lit.