May 19, 2007
Billions of years of cosmic evolution — the birth and death of stars, the slow coalescence of planets, the patient unfolding of life — all...
Circum-axial Leaf Trails
Birthday · May 19, 2007
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APOD published May 19, 2007. Credit: Trudy E. Bell. A publication-date match, not a photo taken on your date. Independent of NASA.
Are photographs of star trails really evidence of the Earth's rotation about its axis? Yes they are, and science journalist Trudy E. Bell discovered that there is a simple way to demonstrate this, if you have the stomach for it. First, find a playground equipped with a standard Merry-Go-Round (MGR) located under or near a large, leafy tree. Seat yourself near the middle of the MGR platform. Ask a local playground expert (KID) to get you spinning very, very fast. As the scenery flashes by at a dizzying rate, point your camera skyward and take a picture with a slow shutter speed setting. The result will be similar to this excellent image of concentric, arcing leaf trails centered at a point corresponding to the MGR's axis of rotation - a convincing imitation of circumpolar star trails recorded in hours-long exposures of planet Earth's night sky. Then, just stand up and walk away ... if you still can.
Image credit: Trudy E. Bell