Astronautics

Astronautics - (alternatively cosmonautics) is the theory and practice of navigation beyond Earth's atmosphere. http://en.wikipedia.org/wiki/Astronautics

Nanoflares

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Total Eclipse

Umbra - The umbra (Latin for "shadow") is the innermost and darkest part of a shadow, where the light source is completely blocked by the occluding body
Penumbra - The penumbra (from the Latin paene "almost, nearly" and umbra "shadow") is the region in which only a portion of the light source is obscured by the occluding body.

Source: http://en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra