Explanation:
What if there were two moons in the sky -- and they eclipsed each other?
This happens on
Mars.
The
featured video shows a version of this unusual eclipse from space.
Pictured are the two moons of Mars: the larger
Phobos,
which orbits closer to the red planet, and the smaller
Deimos, which orbits further out.
The sequence was captured last year by the
ESAБs
Mars Express,
a robotic spacecraft that itself orbits
Mars.
A similar
eclipse is visible
from the Martian surface, although very rarely.
From the surface, though, the closer moon
Phobos
would appear
to pass in front of farther moon Deimos.
Most oddly,
both moons orbit Mars so close that they appear to
move backwards when compared to
Earth's Moon from Earth,
both rising in west and setting in the east.
Phobos, the closer moon,
orbits so close and so fast that it passes
nearly overhead about three times a day.
