It is perhaps a cruel twist of fate that, just when the night air turns coldest and the wind bites most sharply, the night sky is at its brightest, clearest, and most beautiful.
As autumn deepens in the Northern Hemisphere and makes way for winter, the night sky offers up its full glory. For those who enjoy stargazing, the next few months will bring peak viewing conditions.
There are a few reasons why the winter sky is regarded as a special treat for backyard astronomers.
The first is that cold air doesn’t hold as much moisture as warm air can. Summer skies often appear hazier because, actually, they are. The warm moisture-laden atmosphere of summer is thicker, and less transparent, than the crisp, cold winter dome, making it harder to see what lies beyond.
Nights are also longer in the winter, giving us a greater window in which to enjoy the wonders of the universe.
Winter is also the time of year when some of the largest and most dramatic constellations, including Gemini, Monoceros, and Orion the Hunter come out, as well as breathtaking deep sky formations like the Pleiades. Unlike many of the other constellations, which can be dim and difficult to identify, several winter constellations are bright enough for even the greenest sky watchers to pick out.
The final reason the winter sky is so spectacular is simply because the neighborhood we find ourselves facing at this time of year is particularly dark. In the summer, the Earth faces the bright center of the Milky Way. In December, January and February, though, the Earth’s Northern Hemisphere looks out to the edge of the galaxy. Astronomers think the Milky Way contains about 300 billion stars. In the summer time, we’re looking at a greater proportion of those stars. Just like light pollution can make it hard to see the stars inside a city, the brightness of the inner galaxy makes it harder to pick out individual stars in the summer sky.
So while it may sound more pleasant to lie out in the fields and gaze up the stars in the comfort of a breezy summer evening, remember that the winter sky has a magic about it that is worth the extra trouble.