... The Round Earth . ... Aristarchus around 270 BC derived the Moon's distance from the duration of a lunar eclipse (Hipparchus later found an independent method). ... Let R be the radius of that circle and T the time it takes the Moon to go around once, about one month. ... Viewed from Earth, a "new Moon" (occuring between the time a thin crescent is last seen before sunrise and the time one is seen shortly after sunset) happens when the Moon in its apparent motion around the sky overtakes the Sun. ...
Replica of the flagship of Columbus, . ... When Christopher Columbus proposed to reach India by sailing west from Spain, he too knew that the Earth was round. ... The Greek philosopher Erathosthenes went one step further and actually estimated how large the Earth was. ... Erathosthenes established that the direction of the noon Sun differed from the zenith by an angle that was 1/50 of the circle, that is, 7. 2 degrees, and from that he estimated the circumference of the Earth to be 250,000 stadia. ...
... Asteroid Introduction (This Page) . ... Asteroid Summary . Asteroids . Gaspra , Ida & Dactyl , Toutatis , Castalia , Vesta , Geographos, Mathilde . ... NEAR Spacecraft Homepage . Near-Earth Asteroid 3753 - Earth's Curious Companion . ... Then on October 1991 asteroid 951 Gaspra was visited by the Galileo spacecraft and became the first asteroid to have hi-resolution images taken of it. ... Both Gaspra and Ida are classified as S-type asteroids composed of metal-rich silicates. ... Gaspra . ...