Sunday, May 20, 2012
Eclipse of the Sun as Projected through a Palm Tree
During an eclipse of the sun, it's not safe to look directly at the sun itself: your pupil doesn't shut down, because there is not a lot of light. However, the parts of the sun that are still exposed are very intense and can destroy the part of your retina that they hit. If you read anything about the eclipse, you probably heard warnings about this.
Today's eclipse was expected to cause partial blindness in some number of people who looked right into the sun -- it was sure to happen, as health professionals could predict. They probably knew about how many people would be affected, they just didn't know who.
You are supposed to watch the eclipse by projecting the sun's shape through a pinhole or the slit between your fingers onto a piece of white paper -- this effect can be enhanced in various ways. And don't point a camera at the sun either as direct sunlight even during an eclipse can similarly destroy some of the sensors of a digital camera. Or burn through your film if you have a film camera.
Like a pinhole in a piece of cardboard -- the recommended viewing device -- a tree casts a shadow full of little pinholes. Each one projects the same image of the shape of the partially-obscured sun -- but it's much more interesting once you know what you are seeing. The shadows of palm trees against the cottage where we are staying is an example: look at all the crescent shaped images! Aristotle noticed this phenomenon, but I don't think he took a photo.
Update: here is a photo of the shadow of a palm tree in normal sunlight: the projections in the center, where the leaves are close together, are (of course) circles: