When Galileo (http://www.phy6.org/stargaze/Ssolsys.htm#q1C) became the first human to view the Moon through a telescope, our understanding of the Moon changed forever. No longer a mysterious object in the sky, but a sister-world full of ring-shaped mountains and other formations!
Giovanni Riccioli in 1651 named the more prominent features after famous astronomers, while the large dark and smooth areas he called “seas" or “maria" (singular “mare," mah-reh). Some of the names he used for the Moon's crater are of persons discussed in “Stargazers"—Tycho (distinguished by bright streaks that radiate from it), Ptolemy (“Ptolemaeus"), Copernicus, Kepler, Aristarchus, Hipparchus, Erathosthenes; Meton and Pythagoras are on the edge, near the northern pole.
Late-comers who lived after the 17th century had to make do with left-overs: the craters Newton and Cavendish are at the southern edge of the visible disk, Goddard and Lagrange too are near the edge. Also, “Galilaei" is a small undistinguished crater (because of Galileo's banishment?). However, since the Russians were the first to observe the rear side of the Moon, a prominent crater there bears the name of Tsiolkovsky, who at the end of the 19th century promoted the idea of spaceflight.