Here are some of the sky scenes awaiting us in the first half of the coming year.
January 2: The Moon as it emerges into the evening sky passes in front of Venus, then Mars which happens to be passing in front of remote Neptune. So Moon, Mars, and Neptune get into a “trio,” a grouping which gets to fit into a circle with diameter as small as 1.4° on Jan. 3 at 5 hours, Universal Time.
In these pictures, the Moon is drawn at 4 times its real size; Venus, at 150 times, so as to show the lunar-crescent-like shape it is assuming as it swings around the Sun toward us. The Moon is shown also on the previous and next days at the same time; arrows through the other moving bodies, including the Sun, indicate their change of position over 5 days in relation to the starry background. You won’t see, at this twilight stage, all the stars and constellations shown, but they give an idea of what part of the universe you are looking out into.
Comet Honda-Mrkos-Pajdusaková (its designation 45P means it is one of the periodic comets) came in across Earth’s orbit last November and raced through its perihelion on Dec. 31; it won’t reach naked-eye brightness, may be findable with binoculars, but may not develop such an impressive tail.
January 31: Reappearing at the end of the same month, the Young Moon passes the same planets. Venus reached its greatest elongation out into the evening sky on Jan. 12; it will get within little more than 5° of Mars on Feb. 2, but is beginning to fall back toward the Sun.
March 1: Mars, Uranus, and Neptune in the background and Venus in the foreground all sink nearer to the Sun. 2P Encke, famous comet with the shortest orbit, now takes its turn to dive between us and the Sun – its perihelion is on March 10.
April 1: Though Mercury moves out to an elongation of only 18°, the angle at which it does so causes this to be its highest appearance in the evening sky, for those looking from Earth’s northern hemisphere.
April 7: Jupiter rising into the eastern sky at the time of its opposition. Naturally it is at its nearest to the point exactly opposite to the Sun. The approaching Moon will be near that point – in other words, Full – on April 11.
June 3: Venus has swung out into the morning sky, where it is at greatest elongation of 45° on this date. It would stand higher but for the summer-morning angle of the ecliptic.
June 15: Saturn’s turn at opposition, now two and a quarter months after its greater and somewhat faster-moving brother.
For the second half of the year, and more detail on everything, keep checking the “Astronomical Calendar 2017” link above!