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.
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 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.
