A Solar Eclipse For Christmas!

Besides the usual delights of Christmas, this year December 25 will also offer the spectacle of a partial eclipse of the Sun, which will be visible throughout North America except in Alaska. This is the fourth and final solar eclipse of 2000, and the final eclipse of the millennium.

If you add viewing it to your winter festivities, be sure to wear proper eye protection and learn how to view the eclipse safely.

Those in the Eastern Standard Time zone will have the longest viewing period, with the eclipse beginning shortly after 11 am EST and concluding shortly after 2 pm. The extent of the eclipse will vary across the United States, from nearly 70 percent coverage of the Sun in the Northeast to less than 20 percent in the Southwest.

An eclipse of the Sun can only occur when a new moon passes between Earth and the Sun. The moon’s shadow usually passes above or below Earth, but at least twice a year the moon lines up so that some part of its shadow falls on Earth’s surface. The result is an eclipse of the Sun seen from that region.

During the 20th century the Earth had 228 solar eclipses, including 78 partial eclipses. There were 79 years with two eclipses, 15 years with three eclipses, five years with four eclipses, and one year with five eclipses.

There are at least two solar eclipses every year. The rare occasion of five solar eclipses in one year last occurred in 1936 and will not happen again until 2207.

Safe Viewing

Never look through an unshielded telescope aimed at the Sun or even the partially eclipsed Sun. Staring at the Sun, with or without a telescope, without a safe filter can cause permanent eye damage in less than a second. The only time it is completely safe to look at the Sun without a filter is during the “totality” phase of a complete eclipse.

Staring at the Sun under such circumstances is like using a magnifying glass to focus sunlight onto tinder. The retina is delicate and irreplaceable. There is little or nothing a retinal surgeon will be able to do to fix a damaged retina. Never look at the Sun outside of the total phase of an eclipse unless you have adequate eye protection.

One safe way of enjoying the Sun during a partial eclipse, or anytime, is by using a “pinhole camera,” which allows users to view a projected image of the Sun. Elaborate pinhole cameras can be made out of cardboard boxes, but a perfectly adequate (and portable) version can also be made out of two thin but stiff pieces of white cardboard.

Punch a small clean pinhole in one piece of cardboard and let the sunlight fall through that hole onto the second piece of cardboard, which serves as a screen, held below it. An inverted image of the Sun will be formed.

To make the image larger, move the screen farther from the pinhole. To make the image brighter, move the screen closer to the pinhole. Do not make the pinhole wide or you will only have a shaft of sunlight rather than an image of the crescent Sun.

A pinhole camera is meant to be is used with the user’s back to the Sun. The sunlight passes over your shoulder, through the pinhole, and forms an image on the cardboard screen beneath it. Never look through the pinhole at the Sun.

A welder’s mask or the filters for welders’ masks with a rating of shade 14 or higher are safe to use for looking directly at the Sun. They are also relatively inexpensive.

Another safe way to create a filter is by using black-and-white film, but only use true black-and-white film such as Kodak Tri-X or Pan-X; color film or chromogenic black-and-white film, which is actually a color film, cannot be used. You will need to prepare this a few days in advance.

To make a film solar filter, open a roll of black-and-white film and expose it to the Sun for a minute. Have it developed to provide you with negatives. Use the negatives for your filter. It is best to use two layers. With this filter, you can look directly at the Sun with safety.