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American astronomer Asaph Hall discovers Mars's moon Phobos

Phobos () is the innermost and larger of the two natural satellites of Mars, the other being Deimos. The two moons were discovered in 1877 by American astronomer Asaph Hall.

Phobos () is the innermost and larger of the two natural satellites of Mars, the other being Deimos. The two moons were discovered in 1877 by American astronomer Asaph Hall. Phobos is named after the Greek god of fear and panic, who is the son of Ares (Mars) and twin brother of Deimos.

Phobos is a small, irregularly shaped object with a mean radius of 11 km (7 mi). It orbits 6,000 km (3,700 mi) from the Martian surface, closer to its primary body than any other known natural satellite to a planet. It orbits Mars much faster than Mars rotates and completes an orbit in just 7 hours and 39 minutes. As a result, from the surface of Mars it appears to rise in the west, move across the sky in 4 hours and 15 minutes or less, and set in the east, twice each Martian day.

Historical Significance

Phobos () is the innermost and larger of the two natural satellites of Mars, the other being Deimos.

Events Before

  1. The Reichsbank, the central bank of the German Empire, opens in Berlin

    The Reichsbank, the central bank of the German Empire, opens in Berlin

  2. Albert Spalding invests $800 to start a sporting goods company, manufacturing the first official baseball, tennis ball,

    Albert Spalding invests $800 to start a sporting goods company, manufacturing the first official baseball, tennis ball, basketball, golf ball, and football

  3. Julius Wolff opens the Wolff & Reesing Cannery, the first US sardine factory, in Eastport, Maine

    Julius Wolff opens the Wolff & Reesing Cannery, the first US sardine factory, in Eastport, Maine

  4. Alexander Graham Bell and Elisha Gray apply separately for telephone patents, the Supreme Court eventually rules Bell th

    Alexander Graham Bell and Elisha Gray apply separately for telephone patents, the Supreme Court eventually rules Bell the rightful inventor

  5. Sardines first canned by Julius Wolff in Eastport, Maine

    Sardines first canned by Julius Wolff in Eastport, Maine

Events After

  1. First US bicycle club, the Boston Bicycle Club, forms

    The Capital Bicycle Club was an early American cycling club based in Washington, D.C.

  2. Thomas Edison is granted a patent for his cylinder phonograph [1]

    A phonograph, later called a gramophone, and since the 1940s a record player, or more recently a turntable, is a device for the mechanical and analogue reproduction of sound.

  3. 53rd UK Prime Minister Archibald Primrose (31) weds heiress Hannah de Rothschild (27) at the Board of Guardians in Mount

    53rd UK Prime Minister Archibald Primrose (31) weds heiress Hannah de Rothschild (27) at the Board of Guardians in Mount Street, London

  4. W. S. Gilbert and Arthur Sullivan's comic opera "H.M.S. Pinafore" premieres in London, their first international success

    H.M.S. Pinafore; or, The Lass That Loved a Sailor is a comic opera in two acts, with music by Arthur Sullivan and a libretto by W. S. Gilbert.

  5. Congress of Berlin begins, determines the territories of the states in the Balkan peninsula following the Russo-Turkish

    Congress of Berlin begins, determines the territories of the states in the Balkan peninsula following the Russo-Turkish War of 1877–78

More from the 1870s

Belgium disbands its salt tax

Belgium disbands its salt tax

The Moerdijk railway bridge over Hollands Diep in South Holland opens, becoming the longest bridge in Europe at that tim

The Moerdijk railway bridge over Hollands Diep in South Holland opens, becoming the longest bridge in Europe at that time

Japan adopts the Gregorian calendar

Japanese calendar types have included a range of official and unofficial systems. At present, Japan uses the Gregorian calendar together with year designations stating the year of the reign of the…

New York City annexes the West Bronx

The boroughs of New York City are the five major governmental districts that compose New York City. They are the Bronx, Brooklyn, Manhattan, Queens, and Staten Island.

Frequently Asked Questions

What happened on August 17, 1877?
Phobos () is the innermost and larger of the two natural satellites of Mars, the other being Deimos. The two moons were discovered in 1877 by American astronomer Asaph Hall. Phobos is named after the Greek god of fear and panic, who is the son of Ares (Mars) and twin brother of Deimos.
Why is American astronomer Asaph Hall discovers Mars's moon Phobos significant?
Phobos () is the innermost and larger of the two natural satellites of Mars, the other being Deimos.

Explore More

August 17 in HistoryYear 1877