In the Sky This Month

The constellation Cancer rises in the east by around 9 p.m. and climbs high across the sky later on. Its stars aren’t all that prominent, although binoculars reveal a sparkly group of stars known as the Beehive Cluster.

Hamal, the brightest star in Aries, the ram, arcs high across the south this evening, almost directly above the Moon. The star is expanding to become a giant. It is orbited by a giant planet that is being evaporated by the star’s intense energy.

Aries, the ram, is high in the east as night falls and stands due south a few hours later. Despite its fame as a member of the zodiac, Aries includes only three bright stars. A fainter star is added to create a figure that resembles a lopsided boomerang.

The Summer Triangle is in the western sky as night falls. Its three points are Vega, the brightest member of the group, which forms the right point of the triangle; Altair, the left point; and Deneb, the top of the triangle.

As twilight drains from the sky this evening, look toward the west for the Northern Cross. These bright stars represent Cygnus, the swan. As the swan begins to set, though, it dives head-first toward the western horizon, so it looks like a cross.

Look southeast this evening for Sirius, the brightest star in the night sky, which climbs into good view by 8 or 9 p.m. As it climbs away from the horizon its light passes through a thick layer of air, so it twinkles fiercely, changing colors rapidly.

The Milky Way arches high overhead on December evenings. This faint band passes from the Northern Cross, which is in the west, to W-shaped Cassiopeia high in the north, to near the face of Taurus, the bull, in the east.

A poorly known meteor shower should be at its peak tonight. In most years, the Ursids produce no more than a few meteors an hour. That could be the case this year as well, although the shower also could produce a more significant showing.

Winter arrives in the northern hemisphere tomorrow at 10:28 a.m. CST, which is the moment of the winter solstice. The Sun stands farthest south for the year, and it’s the shortest day of the year north of the equator.

One of the nearest galaxy clusters is about 60 million light-years away, in the southern constellation Fornax, which rises in the southeast in early evening. The cluster’s brightest member, NGC 1316, is a beautiful spiral galaxy.