Friday, September 18, 2009

Clockwise & Counterclockwise Sundial Shadows

After writing 'Spiral Dynamics: The Swirl of the 9 and 6', I wondered ... "If the rotation of the Earth on its axis is counterclockwise, then why do the hands of a clock move in the opposite direction ... 'clockwise'?" I found the following explanation:
'The reason "clockwise" was chosen that way was not arbitrary, and has a historical basis. Clocks were invented in the Northern hemisphere and were made to go round the same way as sundials. The shadow on a sundial in the Northern hemisphere goes round clockwise because of the way the sun goes round in the sky. The reason the sun appears to go round the way it does is because the earth goes round anticlockwise when viewed from space looking at the North Pole.' [from; emphasis added]
The first Youtube video below shows this movement in the Northern Hemisphere. The second video shows (among other interesting things) the counterclockwise movement of the sundial's shadow in the Southern Hemisphere:

Related Posts:
* Spiral Dynamics: the Conch and the Earth's Rotation
* Clockwise and Counterclockwise Sundial Shadows: Part II
* Spiral Dynamics: The Swirl of the 9 and 6

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1 comment:

  1. I believe you must be north of the tropic of cancer in order to insure that the sundial shadow rotates clockwise. It all depends on whether or not you must face north or south in order to see the sun. If you must face south, the shadow will rotate clockwise. If you must face north the shadow will rotate counterclockwise. If you are between the tropic of cancer and the Equator, then at summer solstice you must look north to see the sun. But at either equinox you need to look south in order to see the sun. What happens then depends on the time of the year.