05 January 2009

Shadow lengths

From a Jeopardy! clue: to get vitamin D, walk around in the sunlight for at least twenty minutes a day -- but only when the sun is low in the sky. "Low in the sky" is defined as when your shadow is longer than you. That is, when the altitude of the sun is less than forty-five degrees.

The time of Muslim afternoon prayers are also defined in terms of simple arithmetic on shadow lengths.


MikeWebkist said...

Is that true though? I thought you basically couldn't get enough vitamin D from the sun in the winter no matter how long you walked around.

Michael Lugo said...

I don't know. It probably also helps to not cover up your skin with lots of clothing... but let's face it, in the winter that's a bad idea.