Cold nights in December, wonderous views
December — a month which features the longest night of the year— is coming. It will be colder, perhaps snowy, and many will stay indoors on even clear but cold nights. Many beautiful things can be seen on December nights, but perhaps seen only by people who can stand the rigors of the weather.
On a clear December night, look high in the east and find a little group of stars that looks like a small dipper. This group, a great binocular object, has nothing to do with the actual Big Dipper or the Little Dipper. These are aggregations of stars that are directly north, near Polaris, the Pole Star. The group I am describing here is the Pleiades, mentioned in the Old Testament and known by the Greeks as the Seven Sisters.
Technically, groups such as the Pleiades, as well as many others, are known as OB Associations. Stars are grouped by their temperature and spectral class, or color. O and B type stars are young, very hot, white-to-blue-white, and usually quite large — much larger than our Sun. In the case of the Pleiades, you can clearly see the white or blue color with binoculars.
Surrounding the Pleiades, there is a very great deal of interstellar dust. Interstellar dust is made of very small grains and this dust absorbs the red end of the spectrum but lets the blue wavelengths pass through space to our eyes. In long photographic exposures, beautiful, ballooning clouds of this dust are lighted in the same way fog droplets would be illuminated around a street lamp. There are a few people, with very acute color vision, who can see hints of these clouds with the naked eye!
In December, and all winter long, our view of the night sky looks outward from the direction of the core of the Milky Way. Because of changes in the Earth’s orbit, we humans on Earth look out in the direction of the outer arms of our galaxy in winter. Standing almost exactly astride the outer arms of our home galaxy is the constellation Orion the Hunter. The stars that form Orion are much closer to us than the background stars lying behind them that form the outer arms of the Milky Way. Many of these closer stars are some of the brightest we can see with our naked eyes. Just for fun, use a web browser and look up Betelgeuse and Rigel. Betelgeuse, forming the right shoulder of Orion, is a very big Red Giant that looks tawny in binoculars. Rigel is a multiple star that is very big and blue. Rigel forms Orion’s left foot.
But…the real thing to see in Orion is a huge gaseous structure, the scene of much new star formation, designated M42. Look this up on your browser! See the marvelous colors — red, green, and hints of blue. All of these colors are generated by a type of fluorescence caused by the ultraviolet radiation emitted by nearby stars — just like the glows seen by using a ‘black light’ in some underground caverns with some types of minerals. Some years ago, using JBU’s 16inch telescope housed at New Life Ranch, I made a time exposure of M42. I have included it with this article. M42 can be seen in Orion by putting your binoculars on the ‘sword’ hanging from Orion’s belt. Telescopic views are amazing!
I have put together my ‘winter suit,’ consisting of insulated ski pants, a heavy down parka and heavy boots and socks. Under this, I wear wool and then cotton. This seems to work great for me and allows me to spend more enjoyable time under the stars, even in winter, as long as it is dry.
Dress safely but see the beautiful universe in winter.
The New Year cometh nigh…