Seems odd that they go from not being near one another at all (to partially cover) to suddenly being perfectly lined up.
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The moon moves west to east in Earth’s sky, about 13 degrees per day. The moon and sun are just half a degree across, so the time span of eclipses is short, maybe an hour or so.
Perhaps pictures or video will help you understand.
[The Moon’s shadow moving across the Earth as viewed from space.](https://youtu.be/eTN50Qnzh6Q)
[My own video during the 2017 eclipse.](https://imgur.com/a/dTNpVbs)
I went to Cave-In-Rock State Park in southern Illinois to get in the path of totality. In my short video, it was close to totality with just a small bit of the Sun left to cover by the Moon. You can literally see the Sun quickly getting dimmer. I moved the camera away for a moment so you can see a star or planet (I don’t know which) appear above a tree. Then I moved back to the Sun and you can briefly see a dark spot in the center of the Sun. I was using my camera phone to record so I wasn’t using any filters. And you can safely look at the Sun during the eclipse. If you have the sound on, you’ll hear me exclaiming “Oh my God” repeatedly. There were hundreds of people there and you can hear their exclamations as well. It was a very emotionally moving experience for me. I can understand why people feel a religious experience from it.
The sun moves across the sky by it’s own diameter from our point-of-view in about 15 minutes, and the Moon moves a bit faster (again from our POV). If the Moon orbited more slowly, and the Earth turned more slowly, eclipses would last longer even to the extent of lasting days. And if they moved more quickly, the opposite would be true.
As it is, the Moon is directly opposite the Sun as seen from Earth two weeks prior to a Solar eclipse (the Moon rises at about the same time as the Sun sets), then as the Moon orbits it appears to be “catching up” with the Sun getting closer each day, if you go out and watch the sunrise or sunset you might see the “toenail” Moon in the last day or two before the eclipse, after which it approaches too close the Sun (from our POV) and is lost in the glare. The eclipse is only the two or so hours that it takes the Moon to completely pass the Sun in the sky, but it has been “lining up” for a couple of weeks at that point…lining up, but not covering. The covering only lasts a couple of hours. Then, the next day (or maybe two days) you’ll see the toenail Moon again around sunrise and sunset but it will be way off to the side. If you have a local landmark which is between you and the sunset, like a building or a hill, you can watch and see that both the Moon and Sun will set at the identical spot relative to that landmark in the few days both before and after the eclipse, but a month before or a month after they will set at different spots compared to the same landmark.
This is because the Moon and the Sun trace off-set paths in the sky as seen from Earth. If you imagine a race track with steeply banked corners, the cars sometimes take the curve very high on the bank and sometimes very low. The perspective from Earth is that the Moon and Sun take similar paths high or low, and only occasionally line up — most of the time one is high and the other is low, or vice-versa but every once in a while both take the same course as seen by observers on Earth. On a race track, a car overtaking on a curve would cause a crash if it followed the same line as the one ahead and fortunately that part of the analogy doesn’t translate into orbital mechanics, the Sun and Moon are far enough apart that they only *appear* to be following the same line through the sky and they don’t actually collide; but hopefully the analogy is at least a little bit useful.
Seems like there should be a video of this, a cone showing how the shadow of the moon approaches and moves away from the earth around the time of an eclipse. There’s lots of videos, but few have the shadow penciled in.
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