's Viking program
consisted of two unmanned space missions
, Viking 1
and Viking 2
. Each mission had a satellite
designed to photograph
the surface of Mars from orbit
, and to act as a communication
relay for the Viking lander that each mission carried. It was the most expensive and ambitious mission ever sent to Mars. It was highly successful and formed most of the database of information about Mars until the late 1990s and early 2000s.
Viking 1 was launched on August 20, 1975, and the second craft, Viking 2, was launched on September 9, 1975, both riding atop Titan III-E rockets with Centaur upper stages. Each spacecraft consisted of an orbiter and a lander. After orbiting Mars and returning images used for landing site selection, the orbiter and lander detached and the lander entered the Martian atmosphere and soft-landed at the selected site. The orbiters continued imaging and other scientific operations from orbit while the landers deployed instruments on the surface.
Tycho Brahe listen (help·info)
(14 December 1546 – 24 October 1601), born Tyge Ottesen Brahe
, was a Danish nobleman
known for his accurate and comprehensive astronomical and planetary
observations. Coming from Scania
, then part of Denmark, now part of modern-day Sweden, Tycho was well known in his lifetime as an astronomer
In his De nova stella (Of new stars) of 1573, he refuted the theory of the celestial spheres by showing the celestial heavens were not in an immutable or unchanging state of perfection as previously assumed by Aristotle and Ptolemy. His precise measurements indicated that "new stars" (now known as novae or supernovae), in particular that of 1572, lacked the parallax expected in sub-lunar phenomenon, and were therefore not "atmospheric" tail-less comets as previously believed, but occurred above the atmosphere and moon. Using similar measurements he showed that comets were also not atmospheric phenomena, as previously thought, and must pass through the supposed "immutable" celestial spheres.