Barnard discovers Amalthea

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

The 6 December transit was the second in the 1874–1882 pair.

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.

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

Barnard's observation was the last major satellite discovery made visually rather than from photographs.

The new moon orbits closer to Jupiter than the four Galilean moons.

Observers at Sobral and Príncipe took eclipse images to test a prediction of general relativity.

The Brazilian observing site recorded stars whose apparent positions could be compared with earlier images.