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Born on this day
Helena Petrovna Blavatsky
Helena Petrovna Blavatsky was a Russian-German occultist.
33rd week in year
12 August 2024

Important eventsBack

Asaph Hall discovers the Mars moon Deimos12.8.1877

Wikipedia (29 Jul 2013, 14:40)

Deimos is a natural satellite of the planet Mars with an average radius of 6.2 km (3.9 mi), and an escape velocity of 5.6 m (18 ft)/s (20 km (12 mi)/h). It is the smaller and outer of Mars's two known moons, the other being Phobos. 23,460 km (14,580 mi) distant from Mars, Deimos takes 30.3 hours to orbit the planet at an orbital velocity of 1.35 km (0.84 mi)/s. Its systematic designation is Mars II. In English Deimos is pronounced /ˈdaɪməs/ DY-məs; also /ˈdiːməs/ DEE-məs; Greek: Δείμος; also DAY-moce or DEE-moce. In Greek mythology, Deimos was the twin brother of Phobos and personified Terror.


Discovery

Deimos was discovered by Asaph Hall, Sr. at the United States Naval Observatory in Washington, D.C on August 12, 1877, at about 07:48 UTC (given in contemporary sources as "August 11 14:40" Washington mean time, using an astronomical convention of beginning a day at noon, so 12 hours must be added to get the actual local mean time). Hall also discovered Phobos on August 18, 1877, at about 09:14 GMT, after deliberately searching for Martian moons.

It is named after Deimos, a figure representing dread in Greek Mythology. The names, at first spelled Phobus and Deimus, were suggested by Henry Madan (1838–1901), Science Master of Eton, from Book XV of the Iliad, where Ares (the Roman god Mars) summons Dread (Deimos) and Fear (Phobos).

   
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