Star Points for February, 1998; by Curtis Roelle February's Solar Eclipse On February 26th a partial eclipse of the Sun will be visible from Maryland. At 1:14 p.m. EST 22% of the Sun's diameter will be blocked by the Moon's disc. Persons taking a late lunch that day will be able to view the eclipse. The entire partial eclipse will last from 12:22 p.m. until 2:05 p.m. It is possible to safely view the eclipse, and certainly hundreds of thousands of persons in the U.S. and abroad will be. Viewing the eclipse safely would be a wonderful field trip for area schools because the kids need simply to step outside the building to witness it. Direct and unprotected viewing of the Sun can cause permanent eye damage in less than a minute. Damage may occur within one second if the unfiltered sun is viewed directly through a telescope or binoculars. The damage may not present itself until several hours later. The effects, such as blind spots or blurred vision, may be temporary but permanent eye damage might occur. A simple and safe viewer may be constructed using the following materials: piece of cardboard white card or stiff paper aluminum foil pin or needle scissors tape To build: With scissors, cut a one- or two-inch square in the center of the cardboard. Cut piece of foil large enough to completely cover the hole and tape it to the cardboard. With the pin or needle poke a small hole in the center of the foil. To use: Standing with back to the Sun hold cardboard so that it is in sunlight. Place white card a few inches behind the cardboard. Maneuver cardboard and card so that light streaming through the pinhole shines on the white card. This is a tiny image of the Sun. On most days it will look round. But in early afternoon on February 26th it will look more like a cookie with a bite out of it. Do not misuse the pinhole projector by holding it up to your eye and viewing the Sun through the hole! This may risk permanent damage to the eye and is not very effective, by the way. Substitutions: A shoe box and white piece of paper can be substituted for the cardboard and white card, above. Cut a hole in one end of the shoe box and tape the tin foil over the hole. At the opposite end of the box, tape or glue the paper to the inside. Use the pin to punch a hole in the foil as before. The pinhole acts as a "projector" and the white paper as a "screen" in this miniature eclipse theater. According one local optometrist, who happens to also be an avid amateur astronomer, the projected image of the sun of the eclipse theater is perfectly safe to view. This is because much of the dangerous radiation is attenuated by the pinhole, allowing only the on-axis rays to pass through, which by the way are damaging, but the energy is further attenuated by the cardboard or paper which reflects a tiny fraction of the remaining light. One of the few materials considered safe for direct viewing of the Sun is #14 welder's glass. Lighter shades let through more solar radiation and should not be used to view the Sun. For groups I would recommend the pinhole method for two reasons: 1) More than one person can watch at the same time, and 2) proper use requires everyone to view with their backs to the Sun. Refer to the February issue of "Sky & Telescope" magazine for an analysis of various materials and their effectiveness (or lack thereof) as filters for viewing the Sun. Now for questions & answers: Why do we have eclipses? As the Earth orbits the Sun and the Moon orbits the Earth there will occur times when the shadow of the Moon cast by the Sun touches the surface of Earth. This can only happen during "New Moon" when the Moon is between the Earth and Sun. New Moons occur every 29.53 days so why don't we have eclipses every month? If the orbits of the Earth around the Sun and the Moon around the Earth were in the same plane we would. However, the planes are tilted some five degrees with respect to each other. Therefore, eclipses can only happen when the Sun and Moon are located along the line where the planes intersect. I've heard of partial eclipses and total eclipses, so what's the difference? A partial eclipse occurs when an observer sees any portion of the Sun blocked by the Moon (the cookie bite). This month that area includes all points in the U.S. south and east of a line between southern California and upper Michigan. There is also a narrow 92 mile-wide (151 km) path in which the Moon will appear to block the entire Sun. This "path of totality" will cross land in the Galapagos Islands, the Panamanian-Columbian border, northern Venezuela, and several Caribbean islands including Aruba, Antigua, and the volcanically active island of Montserrat. Within this "central path" observers experience darkness as stars and planets appear for several minutes. More spectacular will be the rarely seen pearly-white solar corona and dazzling prominences of hydrogen extending outward from the Sun. Prominences look like ruby-red tongues, each larger than the Earth. When was the last time Maryland was in the "central path" of an eclipse? In 1984 Maryland was in the path of an eclipse of the "annular" type. In an annular eclipse the Moon is farther away making its disc appear smaller than the Sun. Therefore when the Moon is directly blocking the Sun observers in the central path see a ring, or annulus, of bright sunlight around the Moon. Thus the beautiful corona and prominences care not visible during annular eclipses. It rained throughout much of the path that day. I observed the eclipse under a clear sky from Greensboro, NC. The last eclipse of the total type anywhere in the continental U.S. was in 1979; coincidentally it was also on February 26! I observed that it from the snow-covered plains of North Dakota near the Canadian border. When will there be another solar eclipse? A total eclipse will be visible in parts of Europe and Asia Minor in August, 1999. Marylanders have to wait until Christmas day in 2000 when a partial solar eclipse will be visible throughout North America. In the continental U.S. there will not be another total solar eclipse until August 2017, more than 38 years since the last one in 1979! The closest the path of totality gets to Maryland will be southwestern North Carolina. In May of 1994 the path of an annular eclipse passed through the Niagara-Buffalo region of New York state. We took the children out of school for a couple days and successfully observed the ring of golden sunlight. Upon their return to school I was dismayed when they reported at their elementary school the children had been kept indoors during the eclipse because of safety concerns. In Maryland the Moon had eclipsed more than 80% of the Sun. Partial eclipses of that magnitude are infrequent and it was unfortunate that such a wonderful experience for so many was lost. With proper supervision the solar eclipse theater described above can become the basis of a project for school-aged children. They can work as a group in its construction, and then share in its practical use. Sketches of their observations can be the basis for later discussion. In addressing the risk parental approval for participation can be requested. If your home or school has access to the World Wide Web you can see a live video feed of the total eclipse from the Caribbean at http://www.solar-eclipse.org/ on "Eclipse!Live". Eclipses provide a marvelous demonstration of motion in the solar system. With guidance it can become a tool of learning rather than a phenomenon to be feared.