Press Release Observing the Eclipse Williams College--Hopkins Observatory Williamstown, Massachusetts 01267, USA
Professor Jay M. Pasachoff described how and when to observe the eclipse, and how to do so safely while avoiding eye damage. On his 29th eclipse expedition, Dr. Pasachoff is Field Memorial Professor of Astronomy and Director of the Hopkins Observatory at Williams College, Williamstown, Massachusetts, USA. He is also Chair of the Working Group on Astronomy of the International Astronomical Union.
"A solar eclipse occurs when the moon comes between the sun and the earth," explained Pasachoff. "On August 11th, the tip of the moonUs shadow will sweep out a path from the Atlantic through India, making the total eclipse," he said. During the total phase of the eclipse, the sky turns dark in daytime, and the faint outer layers of the sun that are normally hidden behind the blue sky become visible. During the few minutes of totality, scientists can make observations that cannot be carried out in any other way.
"To the sides of the band of totality," Pasachoff explained, "the eclipse is still visible but we see the moon only partially covering the sun. It will look as though a bite has been taken out of the sunUs surface. The size of the bite depends on how far you are from the path of totality. The eclipse will occur in the early morning, and the partial phases will last an hour or two.
"Though the sun will be partly covered," said Pasachoff, "it is still not safe to look at directly. Each bit of the surface of the sun is so bright that it can burn your retina. So if you want to follow the progress of the eclipse, you must take precautions." Pasachoff stressed that the precautions "are the same ones you would take to look at the sun on any ordinary day. The sun does not give off any extra rays during an eclipse. We give out special warnings when eclipses approach because it is much more tempting to look at the sun when an eclipse is going on.
"A pinhole camera is the safest way to observe the partial eclipse," said Pasachoff. "To make one, simply punch a hole perhaps 5 millimeters across in a piece of cardboard, and hold the cardboard up to the sun so that the shadow of the cardboard falls onto a piece of white paper. Look down at the paper, and not up through the hole in the cardboard. In the middle of the white paper, you will see the image of the sun, which will look like a circle with a bite out of it. Often, without making your own pinhole camera, you will find such pinhole images on the ground or on a wall under a tree, since the interstices between the leaves act as natural pinholes.
"If you want to look up toward the sun, you must have a special filter. Ordinary sunglasses are not safe, since they do not absorb anywhere nearly enough sunlight. The filter must block out all but about one part in a million of the light that hits it, and must do so all across the spectrum, even in the infrared. So photographic neutral density filters are not safe either. Special solar filters that block out enough light are commercially available. Or one can make a solar filter by fogging and completely developing black-and-white film to make it black. Color film does not work for this process, since it does not contain silver, and so does not absorb the infrared rays. Even with fogged and developed black-and-white film, try two layers at first, for safety. Further," Pasachoff stressed, "never stare at the sun. Even with a solar filter, just glance through it for a second or two. All you want to do is see how much of the sun is covered. Even through the filter, it is sufficient to take a one-second glance every five minutes."
Reference: Donald H. Menzel and Jay M. Pasachoff, Peterson Field Guide
to the Stars and Planets (Boston, Mass: Houghton Mifflin, 1998).
Jay M. Pasachoff and Michael Covington, Cambridge Guide to Eclipse
Photography (Cambridge University Press, 1993).
jay.m.pasachoff@williams.edu
http://www.williams.edu/Astronomy/IAU_eclipses