A visual search yields Jupiter's fifth moon

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.

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.

Observations from the West African island provided an independent route to the same scientific test.

With the Sun obscured, stars close to its edge became visible; interpretation of the plates came afterward.