Viewing the Sun Safely
Here's what to look for on the solar surface.
Nothing symbolizes unreachable goals so much as a star. To astronomers, stars are inscrutable, featureless pinpoints that yield their secrets only indirectly. All stars, that is, but one. Even a 3-inch refractor will give a dramatic view of the Sun, laying bare its face in high-resolution detail.
The Sun in a telescope is an awesome sight. In apparent size, it ties with the Moon as the largest bright object in the sky. And though it shows fewer features than the Moon, it's a dynamic, living body, changing unpredictably from day to day. The Sun is also the only body hazardous to the astronomer. Without proper protection, even a glimpse of it through a telescope or binoculars can burn the eye’s retina and leave a permanent blind spot.
Two Safe Methods of Solar Viewing
There are two ways to observe the Sun safely: by direct viewing with a proper filter over the front of the telescope and by projection of the Sun’s image onto a piece of paper.
Aperture filters come in two kinds. The most economical is made of metallized Mylar plastic, which usually turns the Sun blue. (Do not stretch the Mylar to remove wrinkles.) Metal-on-glass filters leave the Sun with a more natural tint, are more durable, and cost more. In either case, the best filters have both sides of the Mylar or glass metallized. This keeps the inevitable tiny scratches and pinholes in a single coating from letting sunlight into the telescope, where it would reduce image contrast and possibly threaten the eye. Hold the filter up to the Sun. If bright pinpoints show through, they should be touched out with opaque paint. If the flaws are many or large, the filter should be rejected.
One last caution: Be sure to attach the filter securely to the front of the telescope so wind or a careless finger can’t dislodge it while you’re gazing at the Sun!