Historia, filosofía-biografia-pensamiento

Apollo program, significants missions. Years launched: 1968–72. Country or space agency: US. Designation: 7 through 17. Manned. Events of note: Several unmanned test flights preceded 11 manned Apollo missions, including two in Earth orbit (7 and 9), two in lunar orbit (8 and 10), one lunar flyby (13), and six lunar landings (11, 12, and 14–17) in which a total of 12 astronauts walked on the Moon. Apollo 11, crewed by Neil Armstrong , Michael Collins , and Buzz Aldrin , was the first mission to land humans on the Moon, on 20 Jul 1969. Apollo 13, planned as a lunar landing mission, experienced an onboard explosion en route to the Moon; after a swing around the Moon, the crippled spacecraft made a harrowing but safe return journey to Earth with its crew, James Lovell, John Swigert, and Fred Haise. The six landing missions collectively returned almost 382 kg (842 lb) of lunar rocks and soil for study on Earth. See also: year definition , primitive astronomy

The measure of time on which the calendar is based. It is the time taken for the earth to complete one orbit of the sun. The calendar year consists of an average of 365.25 mean solar days – three successive years of 365 days followed by one (leap) year of 366 days. The solar year (or astronomical year) is the average interval between two successive returns of the sun to the first point of Aries; it is 365.242 mean solar days. The sidereal year is the average period of revolution of the earth with respect to the fixed stars; it is 365.256 mean solar days. The anomalistic year is the average interval between successive perihelions; it is 365.259 mean solar days. [1] See also in Spanish, Año . [1] Year. In a Dictionary of Science, FIFTH EDITION. Oxford University Press Inc., New York, 2005.