Earth and the Moon
What is the best way to observe a solar eclipse?
The Sun’s light is so powerful that looking at it for too long, even during any part of a partial solar eclipse, can cause permanent eye damage. Do not ever look directly at the crescent of a nearly total solar eclipse without proper eye protection. Special sun viewing glasses or filters made of thick Mylar or welder’s glass can be used, but be absolutely sure those filters are properly rated for viewing the Sun, and that they are not damaged in any way.
One safe, indirect way to look at a partial solar eclipse—or the Sun at any other time, for that matter—is by using a simple pinhole camera. Take two pieces of cardboard, one of which has a white surface. Make a small hole in one card by piercing it with a pin. Turn your back to the Sun and hold the card with the pinhole up so that sunlight enters the hole. Now hold the other card, with the white surface facing up, below the first card so that the image of the sunlight through the pinhole lands on the surface. Adjust the distance between the two cards, and bring the Sun’s image into focus. Now you can watch the bottom card to follow the progression of the eclipse behind you.
The one time it is safe to look directly at the Sun without eye protection is during totality of a total solar eclipse. It will only be a few minutes at most, but if you are lucky enough to be there, enjoy the view! Take lots of pictures too, if you have the chance. During totality, ordinary unfiltered cameras will also be unharmed.