Star Travels 
The universe is filled with a hundred billion galaxies or more. Each galaxy contains millions or billions of stars. And many of those stars are likely to have planets -- some of which could be inhabited.
That view of the universe -- a multitude of galaxies, stars, and planets -- began to take shape in the 18th century. And in part, that was thanks to a book by Johann Lambert, one of Europe's leading scientists and mathematicians.
Published in 1761, "Cosmological Letters" posited that the glowing band of the Milky Way was actually the outline of a galaxy of stars that forms a thin disk. Lambert further suggested that each of the stars in that disk was encircled by its own family of planets, and that each planet was inhabited by a multitude of living creatures. And he further suggested that there were countless other galaxies beyond the Milky Way, each with its own stars, planets, and life.
Lambert also suggested that scientists might hitchhike from star to star aboard comets. In our own solar system, some comets visit the inner solar system just once, then head into interstellar space. Lambert's idea said that long-lived races could journey among the stars on such comets, learning about new star systems on each encounter.
It turns out that comets probably aren't very good starships -- although hollowed-out asteroids could be. But many of Lambert's other ideas were spot-on -- and helped shape the modern concept of the universe.
Script by Damond Benningfield, Copyright 2011