Eclipse thoughts
In thinking about the solar eclipse that happened yesterday, one question was on my mind: Why do we need glasses to look at the eclipse? We can glance at the Sun normally and it isn’t described as especially dangerous—but for some reason with the eclipse, there’s all this extra supposed danger; that if you don’t wear special glasses, you can have irreversible eye damage. If you do a search about this topic, you’ll find articles about how you look at the Sun longer than normal during an eclipse, so that’s why it’s dangerous; but that doesn’t seem to be the full story. Is the Sun brighter during an eclipse? What’s going on?
The real story is that the eclipse is a demonstration of Einstein’s theory of relativity—the mass of the Moon causes light to bend. That’s why the eclipse was so important to proving Einstein’s theory over 100 years ago—the famous experiment by astronomer Arthur Eddington was the first real test of Einstein’s theory.
It seems to me that this must be why the eclipse is so much more powerful than normal sunlight—light in bent space appears brighter. Why? The luminosity of the Sun isn’t increasing. The space that the light travels through is bent (light itself doesn’t bend, just the space that light travels in).
The mass of the celestial objects bends space—and when space bends, time also bends—so the light appears closer and brighter to your eye. So glancing at it quickly, as you would at the Sun on a normal day, can do more damage, because the light is occupying bent space that makes it brighter and closer—even though the Sun itself isn’t actually brighter. In fact it is covered up, so it’s darker—that’s the whole point of the eclipse. Paradox.