Posted by: mynaturaldiary | July 11, 2014

Sidereal Motion

Watching the full moon is a delight any time. In the summer, it rises low on the horizon, above the Moor, against the outline of the forest.


Through the scope the detail of the full moon can be seen.

Moon July 2014

Sidereal motion is going on all the time, and yet we barely give it a thought in our daily lives, let alone watch it happening. It’s caused by the rotation of the earth, which makes the stars in the heavens apparently move at night, or the sun rise above the horizon, reach its zenith, then eventually set, lighting our day along its arc.

You can’t do this with the sun for obvious reasons, but watching the full moon through a spotting scope, fixed in position, reveals the sidereal motion. The moon drifts through the field of view, as shown in the following gif, speeded up by a factor of ten.

140711Moon transit

 Si vidi solem cum fulgeret et lunam incedentem clare
If I beheld the sun when it shined, or the moon walking in brightness
Job 31:26

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