Jan Jackson, age 10, of Muncie, Indiana, for her question

How many galaxies are there?

As telescopes become more powerful, they probe deeper and still deeper into the infinite reaches of outer space. And in every direction beyond the Milky Way they reveal more and still more galaxies. This evidence is recorded on photographic plates and gives us a piece by piece picture of the cosmos    or as much of it as we can observe. A galaxy count is limited by how far our most powerful instruments can probe for them.

Stellar astronomy calls for a tedious counting of all the heavenly bodies observable from the earth. From time to time, the charts and catalogs are brought up to date to include masses of new evidence. The latest of these catalogs was published last year. It listed 31,350 outer galaxies by number    only about three of which are dimly visible to human eyes. These galaxies are distinct enough to be clearly identified  ¬and goodness knows how many more there are.