Eli5, what is the definition of a solid angle in physics?
In: Physics
Here’s a topical example: the solar eclipse.
It’s a remarkable coincidence that the moon is just about the perfect size to almost completely cover the sun when it passes in front of it.
Of course, the sun and the moon are not the same size. The sun is much larger, but it’s much further away. You could also pick up a coin and hold it up at the correct length to cover up the sun, and it is much smaller still. But all three of these take up approximately the same amount of space in your field of view. That is their “solid angle.”
To put it another way: you can measure a two-dimensional angle by imagining a unit circle and measuring what length of arc the angle covers, which we call “radians.” You can measure a three-dimensional solid angle by imagining a unit sphere and measuring how much surface area the angle covers, which is called “steradians.”
Latest Answers