I know it takes like 8 minutes for sunlight to reach earth, so does that mean that we experience the eclipse 8 minutes after it happens? I understand that the moon isn’t nearly as far so it’s probably more of just the moon going in front of it, but it confuses me because we still see the ray of sunlight around the moon at totality, so is that light “8 minutes old”?
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Yes, the light is still “8 minutes old” but the eclipse starts when the moon comes between the earth and the sun, not when the photons leave the sun. At the time the light leaves the sun, the moon may not yet be blocking its path, but by the time the light gets there, the moon may be in the way.
The moon is only about 1.2 light-seconds away from the earth, so that’s the actual delay between when the eclipse happens and when you see it.
This question is made complicated by the concept of when does an eclipse “happen” being not well defined. Because it’s an event that takes place when the Moon blocks the Sun from view on Earth, and the Sun and the Moon and the Earth aren’t “in the same time”, which of those times is it really “happening” in?
Did the eclipse “happen” when the observer on Earth saw the sunlight get blocked?
Did the eclipse “happen” when the Sun’s rays that would otherwise hit Earth hit the Moon instead?
Did the eclipse “happen” when the Sun’s rays that will get blocked by the Moon first got emitted from the Sun?
These are 3 different times. And the eclipse is defined as the entire story of events that these 3 things form. It’s .. messy.
All the light you ever see from the Sun is about 8 minutes old. Of course, the exact age depends on how far the Earth is from the sun, which changes throughout the year. But it is always pretty close to 8 minutes, so any photons you see that came from the Sun were emitted by it about 8 minutes ago.
The speed at which the eclipsed area moves across the Earth is not limited by the speed of light, it is limited by the projected speed of the Moon onto the Earth, as you expected. An eclipse is a shadow. The Moon lines up with the Sun and blocks its light from reaching Earth. The Moon is about 1.3 light seconds away from Earth. So when the eclipse is just starting, that last ray of light that reaches you before totality was emitted by the Sun about 8 minutes ago, but passed by the Moon about 1.3 seconds ago. Meaning that you see the eclipse begin and end about 1.3 seconds after the geometrical alignment of the sun, the edge of the moon, and the place you are standing on the Earth.
The Sun’s light took 8 minutes to reach the Earth-Moon system. Some light hits the surface of the Moon, and that light gets interrupted on its journey. We see this happen about 1.2 seconds later because that’s how long it takes for light from the Moon to reach Earth.
We are witnessing the eclipse 1.2s after it happens.
Something like the transit of Mercury across the sun we witness about 5 minutes after it happens because Mercury is so far from the Earth. (Mercury is about 3 light-minutes from the Sun)
The eclipse isn’t the sunlight, it’s the moon casting a shadow on you from the sunlight. So depending on your interpretation, the eclipse could “happen” the moment the shadow falls on you, which is exactly when you experience it, or when sunlight that was going in your exact direction hits the moon, which would be just over 1 second before you would have been in that sunlight.
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