Eclipses of the Moon and Sun

When lighted from just one direction, all objects cast a shadow.  A shadow has two parts: the umbra and the penumbra.  The penumbra (from the Latin paene "almost, nearly" and umbra "shadow") is the outer region of a shadow, in which only a portion of the light source is obscured by the occluding body. An observer in the penumbra experiences a partial eclipse.
The umbra, the inner region, is the darker part of the shadow.  An observer in the umbra experiences a total eclipse. 


Solar Eclipse on Mars
The image on the right is of Phobos (one of Mars' moon) taken by the martian land rover.  The event 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 an annular eclipse of the Sun by Phobos.

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