Thursday, September 3, 2009

Horse Trade

In addition to the center of the galaxy, the spout of the Teapot asterism in the constellation of Sagittarius the Archer points to a whimsical naked-eye object in the Summer Milky Way. This object requires a dark sky to see it, but it’s worth a trip away from city lights.

The object is actually a two-fer, two objects in one economical package. Both are dark nebulas, and they lie across the “star river” of the Milky Way from the Teapot, in neighboring Ophiuchus the Snake Handler.

Dark nebulas (NEBB-yoo-luhs) were once thought to be empty areas in the sky where no stars existed. Now we know they are areas of thick dust— dust so dense it obscures the light of the stars behind it. Dark nebulas are sometimes named for the objects they resemble. It is human nature, after all, to attribute patterns or meaning to random visual events, for example, seeing animals or faces in clouds. This practice even has a name: pareidolia (pronounced pear-eye-DOH-lee-uh).

The first of our two objects is a dark nebula called the Pipe Nebula. You can see from the image below that it looks like the stem and bowl of a smoker’s pipe. This will be the easier of the two shapes to pick out.

For our second object, the Pipe becomes the hindquarters of a horse, and his front half extends away from the Milky Way, as shown in the next image. This is commonly known as the Prancing Horse Nebula.

You should be able to make out the equine's torso and head, as well as his raised front leg.

Here in the American Southwest, this object is more commonly known as the Burro Nebula, or simply the Burro. Burro is derived from the Spanish word for donkey and usually refers to the undomesticated version of that animal. There’s a wild burro population of about 3,800 in the American West. These animals are the descendants of those first introduced into the desert Southwest by the Spanish in the 1500s.

The Burro, with lowered head and upraised leg on the right, hindquarters on the left.
The glowing star cloud above him makes it look as though he is carrying a pack.
© T. Credner & S. Kohle,

You can have your prancing horse. I’ll stick with my burro. He eats a lot less.

Astronomy Essential: The Earth’s magnetic field protects us from the solar wind.

The Earth is a magnetic object, that is, it acts like a magnet, because it has an iron core. As with any magnet, the Earth generates a magnetic field that surrounds it. This magnetic field is called the magnetosphere.

The magnetosphere deflects the solar wind generated by the Sun. The solar wind is a stream of charged particles traveling at over one million miles per hour. Without the magnetosphere to protect it, Earth’s atmosphere would be vaporized by the solar wind.