Igor frolow, age 11, of Milford, Conn.For his question:

Why is Palomar Observatory on a mountain?

Starlight must pierce hundreds of miles of atmosphere to reach the earth. The dancing molecules of air and dust above busy cities play tricks with the star's light beams, and the stars seem to twinkle. We shall get a truer picture of the stars from above the earth's atmosphere  out in space or from the surface of the airless moon.

In the meantime, we build observatories on mountains high above the thick and dusty air. Mount Palomar, near San Diego, Calif., is the home of the huge 200 inch telescope. The big eye weighs 14.5 tons, and it is six million times sharper than your own bright eyes. The far away light it gathers must still come through the air, but it is placed high where the air is as clear and dust free as possible.