by MarkBour » Mon Jun 19, 2017 6:25 pm
Both the Sun and the Moon always appear to travel from East to West in the sky over the U.S. This is caused, in actuality, by the daily rotation of the Earth in the opposite direction. If you look at the APOD video, you can see that the eclipse travels in the opposite direction of the advancing Sun and Moon, travelling from West to East. Why is that, you may ask? Because the Moon is orbiting the Earth in the same direction as the Earth rotates (much more slowly, in terms of degrees covered per day). As a result, the Moon appears to track overhead a little slower than the other celestial objects, losing almost an hour a day compared to them. In the coming solar eclipse, when they align, then, the Sun will appear to overtake the Moon in our sky and pass it, in the race from East to West. Since the Moon is going to be between us and the Sun, then, the shadow it casts on Earth's surface will move in the opposite direction of the speeding Sun. That's one way of looking at it, anyway.
Another viewpoint is to consider that, as I said, the Moon is orbiting us moving West to East. Hence, its shadow will move that direction as well. Its shadow will move faster than the Earth is rotating, so it will progress over the surface of the Earth.
Both the Sun and the Moon always appear to travel from East to West in the sky over the U.S. This is caused, in actuality, by the daily rotation of the Earth in the opposite direction. If you look at the APOD video, you can see that the eclipse travels in the opposite direction of the advancing Sun and Moon, travelling from West to East. Why is that, you may ask? Because the Moon is orbiting the Earth in the same direction as the Earth rotates (much more slowly, in terms of degrees covered per day). As a result, the Moon appears to track overhead a little slower than the other celestial objects, losing almost an hour a day compared to them. In the coming solar eclipse, when they align, then, the Sun will appear to overtake the Moon in our sky and pass it, in the race from East to West. Since the Moon is going to be between us and the Sun, then, the shadow it casts on Earth's surface will move in the opposite direction of the speeding Sun. That's one way of looking at it, anyway.
Another viewpoint is to consider that, as I said, the Moon is orbiting us moving West to East. Hence, its shadow will move that direction as well. Its shadow will move faster than the Earth is rotating, so it will progress over the surface of the Earth.