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Calcium is the fifth most abundant element by mass on earth and the most abundant mineral in your body.

Calcium is the fifth most abundant element by mass on earth and the most abundant mineral in your body.

Earth and Moon from a distance of around 114 million miles.    Taken by Nasa's Messenger deep space probe.

Earth and Moon from a distance of around 114 million miles. Taken by Nasa's Messenger deep space probe.

Forget TV football -- this year's most exciting post-Thanksgiving dinner event will be stepping outside to see Comet ISON on its swing past the sun.  It is estimated that it'll be so bright that it will be visible by day, much as the moon sometimes is.

Forget TV football -- this year's most exciting post-Thanksgiving dinner event will be stepping outside to see Comet ISON on its swing past the sun. It is estimated that it'll be so bright that it will be visible by day, much as the moon sometimes is.

Mars skyline at sunset, pictured from the Viking lander

Mars skyline at sunset, pictured from the Viking lander