A faint Martian point proves to be Deimos

Teams sought to estimate the Earth–Sun distance from observations at widely separated locations.

The 1874 event drew coordinated work across multiple countries and hemispheres.

Hall spotted the first of Mars's two known moons; the recorded date is 11 August in US local time.

Finding Deimos overturned the assumption that Mars had no detectable satellites.

Accounts of the discovery describe Angelina Hall urging her husband to continue looking for Martian moons.

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.

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