Lewis Baker, age 13, of Dallas, Texas, for his question:
How far are the galaxies separated?
Outside the Milky Way, the vast cosmic ocean stretches on and on in all directions beyond human imagination. These limitless reaches of space are well populated with far flung galaxies. Thousands of them are wheels of teeming stars somewhat like our own Milky Way.
There is, it seems, no shortage of galaxies in outer space. The farther we probe with telescopes and radio telescopes, the more we find. Many are spiral nebulae, swarming with billions of stars. Inside these rotating galaxies, the separate stars are far apart. If we scaled each star down to a width of one yard, the average distance between them would be about 10,000 miles. By comparison, the mighty galaxies themselves are relatively closer , together. If we scaled each galaxy down to the width of one yard, the average distance between them would be about 100 yards. This average figure, however, covers a wide variation.
Galaxies do not like to exist alone out there in the isolation of cosmic space. They seem to prefer the company of other galaxies more or less like themselves. They come in twins, triplets and small groups of lOs and 20s. Often hundreds of close galaxies gather~.7; together. in an oval shaped cluster. In some cases, thousands of them form a cloud of close galaxies spanning vast reaches of space. Less than half those discovered exist as lonely islands in the cosmic ocean.
In some groups, the crowded galaxies almost seem to touch each other. Many others are separated by distances more or less equal to their own widths. Twins and triplets, small and large groups, clusters and clouds may be separated from each other by distances equal to a few times their diameters. Twin galaxies may be close enough to overlap. In terms of stars, this would be like placing Sirius partly inside the solar System. Groups may be separated by immense oceans of space.
Our own Galaxy is one of the Local Group. Three of its members are just visible from earth. Two of these are the hazy Magellanic Clouds seem from south of the equator. The third is the stupendous spiral nebula M 31, seen as a dim glow in the constellation Andromeda. Our Local Group has a membership of less than 20 galaxies and part galaxies. It occupies a rather flat, oval shaped section of space. According to one estimate, its volume is about two million light years long and one million light years wide.
Outside our own small group, the next swarm of galaxies lies in the direction of the star Virgo. Its distance is estimated to be about 14 million light years. Its hundreds of close galaxies spread through the immense section of sky behind two entire constellations. In another more remote group, telescope pictures reveal thousands of galaxies in an area of sky about as big as the full moon.
Thousands of galaxies have been photographed, studied and typed. Most of them are : ..xa spiral star systems, roughly the same size or somewhat smaller than the Milky Way. These , are regular type galaxies. The irregular types come in assorted shapes. Some are fuzzy balls of glowing gases with few, if any, well formed stare. Others axe flattened lenses with many stars forming in their glowing gases. Most, if not all, of them rotate. The older galaxies have dense centers of crowded stars and long arms of stars and gases spiralling outward from their nuclei.