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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.
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A
transit of Phobos across the
Sun as seen from
Mars takes place when
Phobos passes directly between the Sun and a point on the surface of Mars, obscuring a large part of the Sun's disc for an observer on Mars. During a
transit, Phobos can be seen from Mars as a large black disc rapidly moving across the face of the Sun. At the same time, the shadow of Phobos moves across the Martian surface.
The event could also be referred to as a partial occultation (or, popularly but inaccurately, a partial eclipse) of the Sun by Phobos.
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Tycho Brahe <phonos file="Da-Tycho Brahe.ogg">listen</phonos> (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 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.