Aug. 17, 1877: Phobos Is Discovered

On 2 July 2026, NASA's Perseverance rover captured Earth disappearing behind Phobos from the surface of Mars — the first time in history a camera on another planet has watched our world vanish behind another object.

From the western rim of Jezero Crater, Earth was not a blue world on 2 July 2026. It was a single bright pixel, 314 million kilometres away, moving across the evening sky of Mars. A thin crescent of Phobos approached from the other direction. Then, for a few moments in an image sequence made by NASA’s Perseverance rover, the pixel was gone. NASA describes this as the first observation made from the surface of another planet in which Earth was se…

On this day in space! Aug. 17, 1877: Asaph Hall Discovers the Martian moon Phobos

On Aug. 17, 1877, American astronomer Asaph Hall discovered Mars's moon Phobos. Moons of Mars: Amazing Photos of Phobos and DeimosHall was working at the U.S. Naval Observatory in Washington, D.C. and looking through a 26-inch refractor telescope — which was then the largest in the world — when he first spotted the moon. Six days earlier, he had discovered another, smaller moon that he first described as "a faint star near Mars." Upon further in…

Aug. 17, 1877: Phobos is discovered

Astronomer Asaph Hall met Angeline Stickney at New York Central College in 1855. Two years his elder, she instructed him in geometry and German, and was reputedly so strong a mathematician that Hall and his classmate made a game of trying to stump her, yet never could. The pair were married the following year. ForContinue reading "Aug. 17, 1877: Asaph Hall discovers Phobos" The post Aug. 17, 1877: Asaph Hall discovers Phobos appeared first on As…

A moon for Mars! Asaph Hall finds Phobos 149 years ago

Asaph Hall discovered Phobos, a moon for Mars, on August 17, 1877. This image of the large crater Stickney on the Martian moon Phobos is color-enhanced. The crater is 5.6 miles (9 km) in diameter, so it covers a substantial proportion of Phobos’ surface. The impact almost destroyed the small moon! Notice the smaller crater within Stickney, about 1.2 miles (2 km) in diameter, resulting from a later impact. Image via HiRISE/ MRO/ LPL (U. Arizona)/…