Of Stars and Drops of Water Moving outward from the solar system: The next closest star to Earth beyond the sun is Proxima Centauri, at a distance of 4.3 light-years (i.e., 4.3 x 6 trillion miles). It is one among billions in our galaxy, the Milky Way. The Milky Way is a pinwheel of stars 2,000 light-years "thick", and 100,000 light-years in diameter. It holds over a hundred-billion (one followed by 11 zeros) stars. The next closest spiral galaxy is M31 in the constellation Andromeda. It is nearly 2 million light-years away (12 million-trillion or 1.2 x 1013 miles). M31 is near the limit of naked eye visibility. The Hubble telescope extends the limit of visibility out to 10 billion (10,000,000,000) light-years. From Hubble, we estimate that there are about 50 billion (50,000,000,000) galaxies in the observable universe! And if each galaxy contains a hundred-billion stars, then the observable universe contains 5,000,000,000,000,000,000,000 ("5" followed by 21 zeros or five "sextillion") stars. By contrast, a cube of water, one inch on a side, contains about 600,000,000,000,000,000,000,000 ("6" followed by 23 zeros, or six-hundred sextillion) molecules! There are 120 times more water molecules in the cubic inch of water than there are stars in the observable universe!!!