Thursday, March 25, 2010

Tripping the Light Fantastic - Part 1

After sunset on winter and early spring nights, you can spot the luminous band of the Winter Milky Way arching across the sky. The cloudlike apparition is the combined light of billions of stars in the spiral arms of our home galaxy. We look at these arms edgewise, from our position within the platter-shaped galaxy.

What we call the Winter Milky Way is the view looking outward, toward the edge of the galaxy. Contrast that with our summertime view of the Milky Way, when we look toward the center of the galaxy.

Let’s trip our way along the Winter Milky Way.

1) About an hour after your local sunset time, face south. If you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your right shoulder to the west, and you’ll be facing approximately south.

Star maps created with Your Sky

2) Moving up from the southern horizon, the first bright star you encounter is Sirius, brightest star in the constellation Canis Major the Big Dog and brightest star in the entire night sky. Extending southward from Sirius is the upside-down-Y asterism (star pattern) of the more prominent stars in Canis Major.

3) Follow the Milky Way up to the next recognizable pattern, the hourglass asterism of the constellation Orion the Hunter. This is a rectangle of stars cinched in the middle by a diagonal line of three evenly-spaced stars: Orion’s Belt.

4) Continuing upward, the Milky Way is next bracketed by Gemini the Twins on the left (east) and Taurus the Bull on the right (west). Gemini is made noticeable by its two brightest stars, Castor and Pollux, the names of the mythological twins. Taurus may be recognized by the V-shaped collection of stars known as the Hyades star cluster, the orange giant star Aldebaran, marking the Bull’s eye, and a spangled cloud above (northwest of) both star cluster and star: the famous Pleiades or Seven Sisters star cluster.

Next week, we’ll trip the light fantastic on the northern end of the Winter Milky Way.