Jerry Petitt, age 11, of Denver, Colorado, for his question;

Has our Galaxy really a sister?

Our Galaxy is but one of billions scattered through the vast reaches of space. Some seem to be fuzzy masses of cloudy gases, Others, like our own, are orderly systems of star dust, gas and millions of suns. These starry wonders may also be called Spiral Nebulae, Island Universes or Milky Way Systems,

Telescope pictures show the countless galaxies scattered through the sky at various angles to the earth. Some are seen edgewise and some flat, Though some are spheres and others irregular, the most common galaxy shape seems to resemble a flat, round lens. Stars and gases are clustered thick in the center and thin out towards the rim. As does our own Galaxy, these giant lenses rotate like wheels.

Very often the starry substance of such a galaxy is thrown out from the center in two spiraling arms. Our own home in the heavens is this Spiral Nebula type of galaxy. So also is the brightest of its sisters,

The galaxies seems to scatter about the heavens in groups. Our own Galaxy is a member of the Local Group, along with at least eighteen more starry sisters, The size of this mammoth family is hard to imagine. Its measurements are calculated in light years ‑ each of which is equal to about six trillion miles ‑ and parsecs ‑ each of which is equal to over nineteen trillion miles.

First consider that our own Galaxy is about 100 light years across and some 10 light years deep at the center. The nearest member of the Local Group is about 86,000 light years across the abyss of outer space, The brightest member of the Local Group is some 750,000 light years distant. It is estimated that our Galaxy and her sisters of the Local Group occupy a space of a million parsecs ‑ more than three and a quarter million light years.

If you know whore to look, you can see the brightest of our Galaxy's sisters. It is a Great Nebula in Andromeda, catalogued as M 31. Andromeda is a fall is a fall constellation, easy to find because it shares the bright star Alpheratz with the Great Square of Pegasus. Your eyes may spot the Great Nebula as a dim blur of light. In telescope pictures it is one of the most glorious spectacles in the heavens. Our starry sister looks like a huge white daisy, gently tipping its head in the rain.

Two other starry neighbors are visible from south of the equator, both fuzzy and irregular. These are the Magellanic Clouds, named for Ferdinand Magellan. The larger one is estimated to be 86,000 light years away and the smaller one 95,000 light years away. Some say these smallish star systems are close enough to be almost a part of our Galaxy.

Not so the beautiful Great Nebula or the Galaxy M 33 which is seen near it in the Triangle constellation. These monsters and others less vast are separate members of the Local Group. So it seems that our Galaxy has at least 18 starry sisters, most likely more. For much of the sky view is hidden behind clouds of gas and star dust in our own system. And even a telescope finds it hard to pick out objects against the blurry background of our own Milky Way.