Venus makes its nineteenth-century return

Repeated observing established that the object was associated with Mars.

Hall found the inner Martian moon days after identifying Deimos.

Phobos's appearance completed the discovery of the planet's two familiar moons.

The newly discovered moon orbits nearer to Mars than Deimos.

With both moons identified, astronomers could study their motions around Mars.

NASA reproduces a photograph of Venus crossing the Sun made by students at Vassar College.

Observers compared records across locations to improve estimates of solar-system distances.

Photographs preserved a measurable visual record of a rare celestial alignment.

Edward Emerson Barnard found a fifth moon of Jupiter.

Amalthea was much fainter than the four large moons seen by Galileo.