Mars has two small, asteroid-sized moons named Phobos and
Deimos. From the point of view of the rover, located near the
equator of Mars, these moons occasionally pass in front of, or
"transit," the disk of the sun. These transit events are the
Martian equivalent of partial solar eclipses on Earth because
the outline of the moons does not completely cover the sun (in
contrast, Earth's moon does block the entire sun during a total
solar eclipse). These eclipses, like those on Earth, occur in
predictable "seasons" a few times each Mars year. As part of a
multi-mission campaign, NASA's Curiosity rover is observing
these transits, the first of which involved the moon Phobos
grazing the sun's disk. The event was observed on Martian day,
or sol, 37 (September 13, 2012) using Curiosity's Mast Camera,
or Mastcam, equipped with special filters for directly observing
the sun. In a series of high-resolution video frames acquired at
about three frames per second for about two minutes, the outline
of part of Phobos blocked