Barry M. Fellinger, age 10, of Chippawa, Ontario, Canada, for his question:
What do we know about the Andromeda galaxy?
The constellation Andromeda is at its highest in the fall though it may be seen at all seasons. Tonight it is rather low in the west, way opposite the Big Dipper. If your eyes are sharp and the skies are not blurred by city lights, you can see a small dim image of this stupendous spiral nebula. This neighboring galaxy in Andromeda was noticed and marked on star charts even before the telescope was invented.
Look for the Great Square of Pegasus, low in the west. The star in the north corner leads to one leg of a long, thin triangle. This triangle is the constellation Andromeda. Near the other leg, at knee level, you may see a small, dim blur of light. This is all that human eyes can see of our glorious sister galaxy. Telescope pictures show it to be an immense spiral star system. Radiotelescopes reveal an even larger picture of its stupendous radiant energies. Astronomers have patiently figured out its size and its distance.
This great galaxy is far beyond the stars of the Andromeda constellation, which belong to our Galaxy. We see it in this constellation because it is located in that direction as we gaze across the oceans of space. Its distance is estimated to be about 1 1/2 million light years, almost 20 times the width of our Galaxy. Each of those light years equals almost six million million earth miles. The width of Andromeda's galaxy is estimated to be about 127,000 light years or about 47,000 light years wider than our own Galaxy.
Astronomers catalog this galaxy as Messier 31, or M31. It is a spiral nebula galaxy of the same type as our own Galaxy. Its thick, brilliant center is packed with stars. From this central hub, wide arms with fewer stars spiral around and out toward the thin edges. The two star systems are sisters, though M31 is larger. There are countless other spiral nebulae galaxies in the universe, but M31 is our closest neighbor.
The dimensions of M31 may astound you. But you tend to forget them when you behold a telescope photograph of the stupendous star system. From our direction across the heavens, we get a slightly edgewise view of the great spiraling wheel. The general shape is an oval. The crowded hub appears as a bright, golden hemisphere in the center. Around it swirl pale streams of light. These are the spiraling arms, made of billions of stars. It is possible to enjoy the glorious beauty of the great galaxy to the full. And we can learn the figures of its size and scope. But our human minds can never quite grasp those stupendous dimensions.
Many human eyes have scanned the skies and spotted that pale blur in Andromeda. This is the limited human view of the brilliant center of the vast star system. Telescope pictures reveal its vast spiraling arms and its hazy clouds of glowing gases. At this distance, its teeming individual stars are out of range. But once in a while an average star explodes and becomes a monstrous nova. Through the years more than 100 nova stars have been observed and clearly photographed in the wondrous Andromeda galaxy.