Tonight, let’s turn toward the northern sky and its famous constellation Cassiopeia the Queen. On December evenings, this constellation appears high in the northeast at nightfall as seen from latitudes in the Northern Hemisphere. Cassiopeia can also be seen from tropical and subtropical latitudes in the Southern Hemisphere, appearing low in the north at nightfall and early evening.
The waxing moon will wash the skies over the coming week. But starting in late December, moonless evenings will showcase Cassiopeia the Queen in all her starry splendor.
In mid-December, Cassiopeia swings directly over Polaris, the North Star, at around 7 to 8 p.m. local clock time. (You can’t see Polaris from temperate latitudes in the Southern Hemisphere because it’s below the horizon in that part of the world.) Cassiopeia – sometimes called The Lady of the Chair – is famous for having the shape of a telltale W or M. You will find this configuration of stars as a starlit M whenever she reigns highest in the sky, hovering over Polaris.
Because Cassiopeia returns to the same spot in the sky about four minutes earlier with each passing day, look for Cassiopeia to be at her high point over Polaris, the North Star, at about 6 to 7 p.m. local time by the month’s end.
From a dark country sky, you’ll see that Cassiopeia sits atop the luminous band of stars known as the Milky Way. Arching from horizon to horizon, this soft-glowing boulevard of stars represents an edgewise view into the flat disk of our own Milky Way galaxy. When Cassiopeia climbs above Polaris, the North Star, on these dark winter evenings, note that this hazy belt of stars that we call the Milky Way extends through the Northern Cross in the western sky and past Orion the Hunter in your eastern sky.
This Milky Way is fainter than the glorious broad band of the Milky Way we see in a Northern Hemisphere summer or Southern Hemisphere winter. That’s because we are looking toward the star-rich center of the galaxy at the opposite side of the year. On these December nights, we are looking toward the galaxy’s outer edge, not the center.
As the night marches onward, Cassiopeia – like the hour hand of a clock – circles around the North Star, though in a counter-clockwise direction.
By dawn, you will find Cassiopeia has swept down in the northwest – to a point below the North Star. At that time, if you’re at a southerly latitude, you might not be able to see Cassiopeia. The constellation might be below your horizon. But if you’re located at a latitude like those in the northern U.S., you will still see Cassiopeia sitting on or near your northern horizon.
Look northward on these cold December evenings to see the Queen Cassiopeia sitting proudly on her throne, atop the northern terminus of the Milky Way!
Bottom line: Watch for the constellation Cassiopeia the Queen on these December evenings. It is shaped like an M or W. You’ll find Cassiopeia in the northeast at nightfall, sweeping higher in the north as evening progresses.