Astronomy in January 2021

The long winter nights of 2021 are a great time to observe planets and stars. The winter constellations of Orion, the Winter Triangle and Canis Major are high in the sky and easily visible to the naked eye. The Moon, which appears full on January 28, is also an ideal target. And if you look closely, you might even spot a comet!

The new Moon on January 13 will be hidden in the Sun’s glare, but it will soon appear as a waxing crescent. It’s an excellent time to explore the Moon’s craters and features with binoculars, and a good opportunity to check out NASA’s high-resolution Moon image map (click this link).

Mercury is back on the observing table in early January as it reaches its greatest eastern elongation for 2021 on January 23. Look for this inner planet in the twilight sky, about an hour and a half after sunset. It will be positioned almost exactly between Saturn and Jupiter, forming an equilateral triangle in the southern twilight. Mercury will stand a little above magnitude -0.6 Jupiter and 1.4deg due south of Saturn, creating an elegant pairing in the evening twilight.

Observe this fascinating trio with a telescope to see their distinct shapes and the fine details of these two enormous gas giants. And don’t miss the chance to glimpse Uranus, which lingers close to red-beacon Mars this month, sticking its tail between Mars and star 19 Arietis in southern Aries. With a telescope, this ice giant will shine with a blue-green color and look distinctly different from the nearby stars, which twinkle brightly.

This is a busy month for the outer planets, with Jupiter, Saturn and their moons all in action in the evening sky. Watch for Venus rising over an hour before the Sun on January 1, shining a 94-percent-lit disk low in the southeast as twilight begins. It will reach 98 percent brightness by the end of the month.

After setting for the day, Jupiter will reappear in the morning sky in mid-January, low in the east-southeast as dawn breaks. It will remain visible for another week, until it reaches conjunction with the Sun on February 28.

A waning crescent Venus will dominate the sky on the evenings of January 26-27, appearing as a bright golden star low in the west-southwest in early evening twilight. It will then move to the east and cross into Orion, the belt of brilliant stars that marks his shoulders and torso. It will be joined by the waning crescent Moon, and together these two bodies will form a stunning sight. As evening twilight fades, the Moon will join Jupiter and Saturn in a richly-textured evening sky, presenting a dramatic display of our solar system’s largest planets and their many moons. The ringed planet Saturn will also be brighter than it was last month.