In the Sky This Month

Regulus, the bright heart of Leo, the lion, shines close to the gibbous Moon the next couple of nights. The star is below the Moon as they climb into view by midnight tonight.

The twins of Gemini arc high across the sky on December nights. Right now, the constellation is low in the east-northeast by about 8 p.m. and passes almost directly overhead in the wee hours of the morning.

Although the shortest day of the year, the winter solstice, is almost three weeks away, much of the United States is seeing the earliest sunsets of the year about now. The date of earliest sunset varies with latitude, with the date getting later as you go north.

Even though winter is almost here, the Summer Triangle remains in good view. It is well up in the west at nightfall. Its brightest point is the star Vega, more than a third of the way up the sky. Deneb is above it, with Altair far to the left of Vega.

The planets Jupiter and Saturn are in the southwest as night falls. Jupiter is the brighter of the two — brighter now than anything else in the sky at that hour. Saturn is a couple of degrees to the upper left by about the width of a finger at arm’s length.

Venus, the “morning star,” stands above the star Zubenelgenubi at dawn tomorrow. Although it officially belongs to Libra, the balance scales, the star also represents the southern claw of the scorpion. Venus and the star will stand side by side on Friday morning.

The full Moon will fade a bit early tomorrow thanks to a penumbral lunar eclipse. The Moon will pass through the faint outer ring of Earth’s shadow. Most of the lunar disk will take on a dusky appearance, as though it were covered by a thin layer of clouds.

The Moon arcs high across the sky tonight. It rises in the east-southeast before sunset and sets in the west-northwest before sunrise. The Moon’s rising and setting points move north and south along the horizon, with a big swing between the monthly extremes.

Cetus, the whale or sea monster, is in the southeast as night falls, to the right and lower right of the almost-full Moon. Among its treasures are two beautiful galaxies, Messier 77 and NGC 1055. Both are giant spirals like our home galaxy, the Milky Way.

Perseus the hero is in the northeast at nightfall. Its brightest star is Alpha Persei, a massive young star that’s nearing the end of its life. It is surrounded by a family of hundreds of other stars known as the Alpha Persei Cluster.