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Partial Solar Eclipse Will Occur on Christmas Day

by Thomas L. Rokoske

(NOTE: Dr. Rokoske is a professor in Appalachian State University’s Department of Physics and Astronomy)

BOONE — The last solar eclipse of this millennium will occur on Christmas Day.

The eclipse will be visible across most of the North American continent and can be seen across Western North Carolina starting at 10:50 a.m., weather permitting. The eclipse will end around 2:10 p.m. The eclipse will be visible a few minutes later across Eastern North Carolina.

A solar eclipse occurs only at the New Moon and when the moon passes between the earth and sun when the planets’ geometry lines up so that some part of the moon’s shadow falls on earth’s surface.

An eclipse simulation is located on the Goddard Space Flight Center web site:

The amount of eclipse will range from 48 percent to 50 percent with the largest amount of eclipse visible in the northern part of Western North Carolina near Sparta and Mount Airy. The maximum part of the eclipse will occur around 12:30 p.m.

There are three safe methods for viewing a solar eclipse. One is the shadow projection or “pinhole” technique, the second is viewing through a “mirror pinhole” and the third is viewing through welder’s glass.

The safest and most inexpensive of methods is by projection, in which a pinhole or small opening is used to cast the image of the sun on a screen placed three feet or more beyond the opening.

To use the shadow projection technique, make a clean hole in the top of a cardboard box. Choose a box about the depth of a shoebox and make the hole about 3/16″, or the size of a 16-penny nail. There should be no other holes in the box. Trim the excess waste from the hole so that it will not block the light. Hold the top of the box toward the sun. Remove the top of the box and hold it about three feet from the bottom. Position the bottom of the box so it is in the shadow of the top of the box. The sun’s image will be projected on the box bottom.

If you have access to a long focal length lens, you can magnify the size of the image of the eclipsed sun. First enlarge the hole in the top of the box just enough to hold the lens, then secure it with tape. Use a lens with a focal length of 40 inches (100 cm) or greater. Once assembled, separate the top of the box from the bottom by a distance equal to the focal length of the lens and you will see the magnified image of the sun.

A small mirror tile can be used as a type of “pinhole” to reflect the light of the solar eclipse on the ceiling of a room. Place a mirror tile 3/8″ x 3/8″ on a windowsill of a darkened south-facing room. Mirror tiles can be found at hardware or art supply stores, or you can make one by covering a small mirror with black tape, except for a 3/8-inch-square area. A front surface mirror works best.

If you have access to a No. 13 or 14 welder’s glass, hold the glass toward the sun and look directly through it. Welder’s glass can be purchased at most welder’s supply stores.

There are safe solar filters available from some telescope suppliers.

Never look at the sun with a telescope or pair of binoculars without using a solar filter over the objective lens or over the top opening of a reflecting telescope. An objective lens pointed directly at the sun can be cracked by the heat of the direct sunlight.

Never look at the sun through sunglasses as that will damage your eyes.