Brian DesJardins, age 12, of Carp, Ont., or his question
What is the Great Nebula in Andromeda?
This is good time of year to get a faint glimpse of one of the greatest wonders in the heavens. For Andromeda is a constellation, appearing just east of the great square of Pegasus. Andromeda is shaped like a broken dart and the top star, Alpheratex, is one of the stars in the great square. In the ancient pictures of the constellations, this star marked the head of Andromeda. Her chained hand extended down one side of the dart. Near it, if your eyes are good and the sky very clear, you can see the famous Nebula as a faint blur.
Your eyes alone can see little or nothing of this starry wonder. A powerful telescope will show it to be a faraway galaxy, a twin to the starry Galaxy which is our own vast home in the heavens. Our eyes see only a faint blur because the light from this faraway wheel of stars set out to reach us one and a half million years ago. A light year is about six million, million miles and our Galaxy and its twin are separated by a million and a half light years.
If there were a beauty contest in the heavens, this great nebula would certainly be named Miss Universe. And naturally, she appears ather best when photographed. The pictures are taken through powerful telescopes in sections and fitted together. The dazzling portrait shows a wheel of stars with a luminous center and pale arms spiraling outward. Our view is somewhat edgewise across the flat circle so that the stupendous galaxy looks like a giant daisy bowing its head in the rain.
Such vast star systems are called island 'Universes, because they are separated by vast oceans of outer apace, They are called spiral nebulae because of the long starry arms which spiral out from the dense nucleus. They are called Milky Way systems because they resemble the Milky Way, which is a cross section of our own Galaxy.
We also can call them galaxies and our own home in the heavens the Galaxy, with a capital letter.
In size, the Great Spiral Nebula in Andromeda is somewhat larger than the Galaxy, which is now thought to be about 10,000 light years from side to side. The width of the Andromeda nebula is now estimated to be some 120,000 light years. The width of its spirally arms is 2500 light years and the distance between them about 10,000 light years. The vast wheel of stars is very thin and the densest star population is concentrated in the glowing center. Though somewhat smaller, the Galaxy is similar in shape to its sister galaxy.
The Great Nebula has been under close observation for many years. From time to time, a bright nova or a supernova bursts forth in the system. And in the past few years the radio telescope has detected energy pouring forth from this faraway powerhouse of stars.