Mars is the fourth planet from the Sun in our solar system. It is named after the Roman god of war Mars (Ares in Greek mythology) because of its apparent red color. This feature has also earned it the nickname "The Red Planet". The prefix areo- refers to Mars in the same way geo- refers to Earth. The astronomical symbol for Mars is ♂, a circle with an arrow pointing northeast. The Chinese, Korean, Japanese, and Vietnamese cultures refer to the planet as 火星, or fire star. Mars is a terrestrial planet with a thin atmosphere, having surface features such as craters, giant valleys, and volcanoes. Of all the planets in our Solar System other than Earth, Mars is the most likely to harbor liquid water, and perhaps life.
As part of the wider Mariner program, in 1969Mariner 6 and Mariner 7 (Mariner Mars 69A / 69B) completed the first dual mission to Mars, flying over the equator and south polar regions and analysing atmosphere and surface with remote sensors as well as recording and relaying hundreds of pictures. The mission's goals were to study the surface and atmosphere of Mars during close flybys to establish the basis for future investigations, particularly those relevant to the search for extraterrestrial life, and to demonstrate and develop technologies required for future Mars missions and other long-duration missions far from the Sun. Mariner 6 also had the objective of providing experience and data which would be useful in programming the Mariner 7 encounter 5 days later.
Tycho Brahelisten (help·info) (14 December 1546 – 24 October 1601), born Tyge Ottesen Brahe, was a Danishnobleman 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 and alchemist.
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.
