Once again: like hiking in the woods, riding a bicycle, or cooking on an outdoor grill, eclipse viewing is safe, enjoyable and worthwhile if you equip yourself with some basic information and take simple precautions.
It is never safe to stare directly at the bright disk of the Sun. Too much of the Sun’s direct light can damage your eyes without your knowing it, because the retina, the part of the eye that detects light, has no pain receptors.
Safe solar viewing methods
1. Looking through specially-made solar filters or “glasses”
The only safe way to look directly at the uneclipsed or partially eclipsed Sun is through special-purpose solar filters, such as “eclipse glasses” (like those for sale at RMSC while supplies last) or handheld solar viewers. Homemade filters or ordinary sunglasses, even very dark ones, are not safe for looking at the Sun. Check your glasses or viewer for a label saying that the filter material conforms to ISO 12312-2, the international standard for filters for direct observation of the Sun. (Celestron, a reputable maker of telescopes and binoculars, uses a “Solar Safe” logo to represent its compliance with ISO 12312-2.) Some solar viewing filters are black, others are silver in appearance. Here are some materials that are NOT safe for solar viewing:
- CDs – not safe for solar viewing
- Mylar party balloons – not safe for solar viewing
- Laser show or fireworks glasses – not safe for solar viewing
- 3D glasses (red-blue or any other kind) – not safe for solar viewing
RMSC has ISO 12312-2-compliant eclipse glasses for sale while supplies last.
2. Looking at a projected image of the Sun
Any small hole will project an image of the Sun on a light-colored screen. Try this: use a no.2 pencil point, a knitting needle, or the point on a school compass to poke a hole in a card. That’s your “pinhole.” Hold another card that is white or light-colored (your projection screen) in the shadow of your pinhole card about an arm’s length away. Look for a little circle on the screen. That is an image of the Sun. During the partial eclipse, that circle will become a crescent. You will probably find the image to be washed out by ambient light from the sky and your surroundings. You can use some kind of box to hold the pinhole at one end and the projection screen at the other end. The box gives shade on the projection screen, making the image easier to see.
Before eclipse day, experiment with different-sized holes and with different distances to the screen. What combination gives you the brightest image? The sharpest image? To make a very small pinhole, try puncturing a small piece of aluminum foil. Then tape that over a bigger hole in the cardboard. If you are in a big, open building, such as a barn, with tiny holes or vents in the roof, look for Sun images on the floor. If the roof is high above the floor, the images will be large and sharp. A straw hat, kitchen colander, or anything else with many small holes will project a pattern of crescents during the eclipse.
SOLAR VIEWING WITH SOPHISTICATED EQUIPMENT
Experienced amateur and professional astronomers have ways of using telescopes and other equipment to view or project the Sun safely. Telescopes are designed to concentrate light, and concentrated sunlight can be dangerous if not handled knowledgeably. So you may hear about neutral-density filters, Sun stops, hydrogen-alpha filters, and other solar observing technologies. Volunteer amateur astronomers, including folks from the Astronomy Section of the Rochester Academy of Science, plan to set up a few such devices at RMSC on eclipse day – so you don’t have to!
When pinhole-projected, the size of the Sun’s image will always be about 1/100 of the distance from the pinhole to the surface where you see the image. So, for example, if the surface is 100 inches (about 8 feet) from the pinhole, the Sun’s image will be about 1 inch wide.
The shape of the pinhole doesn’t matter much, as long as the hole is small and not too close to the screen. The hole can be a triangle or a square; it will still make a circular image of the Sun’s disk.
The Sun’s outer atmosphere, called the corona, is safe to look at, but only when the Sun is totally eclipsed.