- Giovanni Schiaparelli (1835-1910)
- Born in Italy.
- He did studies of comets and meteor streams.
- He discovered the asteroid Hesperia.
- He drew maps of Mars, the best of his day.
- He revised the names of features on Mars. He found long, straight lines on the planet, and called them canali.
- Born in Estonia.
- He made mirrors and lenses for telescopes.
- He devised a means to photograph wide areas of the sky with a single plate, with the definition sharp across the whoe of the field.
- Born in Germany.
- He made many drawings of the Moon, and made measurements of the heights of its mountains.
- He made maps of Mars and Venus.
- He recorded the faint luminosity on the night side of Venus.
- He and members of his committee discovered the first four asteroids.
- Born in Germany.
- He was the first to discuss black holes, and presented theories about them.
- Born in Italy.
- He originated the classification of stars by spectrum analysis.
- Born in USA.
- He showed that Cepheid variables are pulsating stars, not eclipsing binaries.
- He calculated the diameter of our galaxy.
- He discovered that globulars are not spread uniformly across the sky and are most common in the south.
- He identified two dwarf galaxies in Sculptor and Fornax.
- Born in USA.
- He measured the rotation periods of the planets.
- He measured the speeds of spiral nebulae, discovering that they must lay beyond the Milky Way.
- He and his assistants located Pluto.
- Born in Germany.
- He founded the study of double stars.
- He published a catalogue of over 3,000 binary stars.
- He carried out one of the first determinations of stellar distance.
Bernhard Schmidt (1879-1935)
Johann Schröter (1745-1816)
Karl Schwartzschild (1873-1916)
Pietro Angelo Secchi (1818-1878)
Harlow Shapley (1885-1972)
Vesto Melvin Slipher (1875-1969)
Friedrich Georg Wilhelm Struwe (1793-1864)