The following article was written in 1979 in anticipation for the eclipse.
Moscow could provide its residents with prime seating Monday for, one of nature’s most spectacular light shows. The town is in the path of totality, the full moon shadow, for the last solar eclipse to hit the continental U.S. this century.
But access to the action has accompanying hazards as well as advantages.
The eclipse will begin at 7:20 a.m., when the moon just starts to come into view, and end at 9:31 a.m., when the last bit of the sun again becomes visible. Totality, the period when the moon obscures all but the sun’ corona, will be two minutes and eight seconds long, from 8:19:49 to 8:21:57.
Clouds could curtain the spectacle’s most dazzling aspects, but Moscow will still experience daytime darkness. Weather Bureau statistics give Moscow about a one in six chance of clear weather and a one in 10 chance of partly cloudy skies, according to an information sheet from the physics department. The spectator sitting in one place has about a 20 percent chance of viewing the eclipse in a clear sky or through a hole in the clouds. Being prepared to drive around could increase chances to 25 percent.
The phenomenon carries with it the hazard of permanent eye damage. Viewing it isn’t dangerous if one follows proper procedures, but viewing the eclipse unprepared can mean burning a hole in the eye’s retina.
When the moon passes before the sun, the earth in the shadow’s path will be dark. The eye’s lens will open to adjust to the darkness, just as it does outdoors at night or in a dark room.
But, just before the sun is completely covered and just as it reappears, there will be a sliver of sun in view that’s as bright as ever. That sliver can burn a crescent-shaped hole in the eye’s retina.
Several devices can provide safe eclipse watching.
Probably the best method is to project the eclipse image through a pair of binoculars onto a white card. Binoculars must never be used to look directly at the sun. But if the viewer, back to the sun, holds the binoculars about waist level, points the front toward the sun, and holds a white card about 18 inches behind the eye piece, he can watch the eclipse projection on the card.
For the viewer without binoculars, two thicknesses of exposed, developed black and white film make an adequate filter. One thickness isn’t enough. The film must be exposed enough to completely blacken it. Color film won’t do, because it allows infrared light to pass through. The eye won’t see the infrared light or immediately feel the burn, but it will be damaged just the same.
Another protection is a welder’s glass with at least a No. 14 rating, Ingerson said.
No matter what protection the spectator uses, he should not stare at the eclipse.
Devices that should not be used, besides color film, include smoked glass and photographic neutral density filters. Both transmit infrared rays.
While the moon is directly before the sun, the sun’s corona, or outer atmosphere, will be visible. This is the only time the corona is visible to the human eye. The corona will be an eerie purple-blue light around the moon with dancing flames, or projections.
The corona, during the period of totality, may be viewed with the naked eye. But unprotected corona viewing can leave one vulnerable to eye damage when the sun reappears. Seeing the corona is an almost hypnotic experience, Ingerson said. It’s easy for the spectator to become mesmerized and forget to grab his filter before the sun’s edge flashes back into view. It takes as little as 1/100 of a second for retinal damage to occur, Ingerson said.
Photographing an eclipse presents the cameraman with some peculiar difficulties. The camera lens must be covered with an appropriate filter. Either a 5.0 neutral density filter or a No. 14 welder’s glass will work. So will two sheets of exposed, developed black and white film, but they may reduce optical quality. Improper covering can result in a fried camera interior, Ingerson said.
Again, a neutral density filter does not block out infrared rays. Looking through the viewfinder of a single lens reflex camera equipped with such a filter is not safe. Nor is looking through the viewfinders of many other types of cameras without using a proper shield.
The eclipse will present some special phenomena. Since the sun is at a period of sunspot maximum, the corona should be especially large and active. Just before and just after totality, as the light of the sun appears and disappears behind the mountains of the moon, the edge of the moon may be covered briefly with dancing lights called “Bailey’s Beads.” These should not be looked at without a filter or binocular projection.