Photo of the Month
Photographing the Center of our Galaxy
When you view the Milky Way in the night sky, you are actually looking at our own galaxy. That galaxy has the shape of a flattened spiral with multiple “arms” containing about 200 billion of a variety of stars, including our sun, and extends approximately 100,000 light years in diameter. Given that a light year is the distance light travels in a year and that our planet is almost 100,000 light years from its most distant galactic neighbors, the light you see from many of the stars departed from those stars almost 100,000 years ago—so you are looking at our galaxy as it was in the past, not as it is today. As you look at the southern part of our night sky toward the constellation Sagittarius, you are looking toward the center of our galaxy, the part that displays the highest density of stars. The portion of the Milky Way in Sagittarius is so dense with stars that the Milky Way takes on a look of a diffuse cloud in the night sky, as you can see from this image.
Sagittarius is one of the twelve constellations in our zodiac, which is a band of constellations along our celestial equator. The sun spends roughly an equal amount of time in each constellation during the Earth's one year trip around the sun; those times approximate twelve one-month periods when the sun is in each constellation, periods that are often referred to as “signs” of the zodiac. The constellations are referred to by names of the images suggested to ancient stargazers by the pattern of stars in the constellations: for example, Sagittarius is the Latin word for “archer,” and so Sagittarius is usually depicted as a centaur with a drawn bow ready to release an arrow. (The constellation is also referred to at times as Centarus.)
Anyone can take this photo if you can escape city lights and find a dark, moonless sky. This photo was taken with a Canon 1Ds Mark II using a tripod with an ISO setting of 1600, with the exposure set at 30 seconds and the aperture set to f / 2.8. Use a wide angle lens set at your widest angle or the shortest focal length. The image may also need a little PhotoShop touch-up.