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Why Does The Eclipse Move From West To East?

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We’ve been getting a lot of questions about the upcoming Great American Solar Eclipse, and one question in particular — why does the shadow move from west to east when we know the “Sun rises in the east and sets in the west”?

It’s all related to the Earth’s counter-clockwise rotation around the Sun, and the Moon’s counter-clockwise rotation around the Earth. Take a look.

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1 Susan Higgins { 08.24.17 at 4:32 pm }

Hi July, we asked Joe Rao your question and here is his response. We will also email you this information:
“In answer to question #1, it depends on the time of the year. In the summertime, the Earth’s Northern Hemisphere is tilted toward the Sun . . . in the winter it is tilted away. Also, it depends on the node — that point in the sky where the New Moon intersects the ecliptic (the Sun’s path against the background stars). For this most recent eclipse, the Moon arrived at its ascending node, but had it occurred at the descending node, the path traced across the Earth would have appeared a bit different.
In answer to question #2, almost always, the dark shadow cone of the Moon (the umbra) first strikes the Earth at local sunrise. The shadow then streaks rapidly across the Earth at thousands of miles per hour until it leaves the Earth’s surface some 8 or 10 miles away to the east at local sunset. In our recent eclipse, the shadow first touched the Earth about 1,500 miles northwest of Hawaii where the Sun was rising over the Pacific Ocean. It left the Earth’s surface just over three hours later a few hundred miles to the west of the Cape Verde Islands, in the Atlantic Ocean, where the Sun was setting.
And along the way, it passed over the United States around the middle of the day.”

2 July { 08.24.17 at 5:13 am }

Hey, I was just wondering howcome the totality of the Solar Eclipse changes path directions each time, like this time it taking a Southeasterly motion across the US, and next time in April 2024, taking more of a Northeasterly motion from the looks of it, as some examples? I know the moon moves in the same direction as the earth from west to east, but just not sure why the path of the Solar Eclipse Totality doesn’t just go straight from West to East each time in any given location on the planet earth. I been trying to look for an answer by typing in that question on google and not getting the best results yet, so I figured I tried to see on here if possible. Quite awesome tho!

I’m also wondering, do Solar Eclipses generally begin at the start of the day of the new moon like during Sunrise wherever the path begins and end at Sunset the day of the new moon where the totality path ends, or does it usually vary each time? This applies from start to finish altogether, even while out to sea. I’d be interested in knowing more about that one as well.


3 Susan Higgins { 08.23.17 at 4:21 pm }

Hi Derrick, Hopefully you saw yesterday’s eclipse, and the coverage of it. The shadow started in the west, in Oregon, and swept across the United States in a swath that took about 90 minutes, until it finished up in South Carolina. That is a west-to-east path. Unfortunately, we can’t debate this with you over our web site, and what occurred before our very eyes; if the video was not helpful, perhaps you can consult an astronomer that you trust.

4 Derrick { 08.23.17 at 1:47 pm }

since the moon travels east to block the sun to create the eclipse, the shadow of the moon will start in the west then travel east. BUT the earth rotates way faster than the moon orbit so we will always see the shadow from east to west. No matter what!

So the only way for the moon to cast a shadow from west to east is if
1. The earth and sun didn’t rotate and the moon was between the two orbiting east
2. The earth doesn’t rotate and the sun and moon orbit the earth west with the sun orbiting faster.
3. The earth, all of a sudden, started rotating west with the moon orbiting east around the earth with both orbiting the sun east. Which is impossible cause the sun and moon rise in the east and sets in the west.

Since none of those thing are possible I’d say there’s something strange going on about what we’ve been taught all our life and it took this one incident to bring it to light…stay woke.

Don’t overcomplicate things by talking about standing high over the North Pole and other nonsense.
Use the information the scientific community gave you and you can clearly see without a doubt, that it is not possible for the moon to cast a shadow from west to east. It’s just common sense.

5 Ken W. { 08.21.17 at 11:01 am }

A pretty great lesson in relativity, actually. We think of the moon and sun as traveling the sky from east to west because it’s not typically useful to us to think of the earth spinning beneath our feet, or the position of the earth in its orbit around the sun. Where an eclipse is concerned, those motions become relevant — and we need to change our point of reference.

6 Phil { 08.20.17 at 9:09 pm }

John’s explanation nails it for me much better than the videos. It makes since to me if I just think of the moon as a giant tree.

7 Laughing out loud { 08.20.17 at 3:07 pm }

This made absolutely no sense. Tony is right. They need to pick a position. The shadow is in question, not the source. Notice how they stopped the Earth from spinning to illustrate the shadow going west to east.

8 Susan Higgins { 08.20.17 at 11:47 pm }

Hi Tony, the shadow will go west to east. It will start in Oregon and move eastward. The video explains why this happens. You are correct though about the Moon’s speed. This is also addressed in the video.

9 Tony Reynolds { 08.20.17 at 11:27 am }

The shadow would not go west to east. The Earth rotates faster then the moons orbit around the Earth. So the shadow should be falling behind, appearing from East to West.

10 John { 08.19.17 at 6:49 pm }

Got the Answer!!! Why is the eclipse moving from west to east? Because the Earth rotates the moon “rises” in the east just like the sun. The moon is going around the Earth in the same direction as the Earth is rotating. This is why the moon goes around the Earth every 29 days but by our view it is every 28 days. I know it is like if you drive north and pass a car that is going north slower, it looks like that car is moving backwards. So what is the difference between the rotation of the Earth and us seeing the moon (moonrise) and the rotation of the Earth, and us seeing the moon between Earth and the sun. If moonrise is always in the east why is the eclipse, the shadow of the moon, starting in the west? Not clear to me and I have the same number of degrees as the Professor on Gilligan’s Island.
Ok Possible answer. None of the YouTube videos made this point. They talked and talked and sounded so smart but didn’t really answer the question. Then I remembered telling kids that if you know the path of the Sun, it will help you find a good place to park. Shadows move from left to right – west to east – with the shortest shadow pointing north. The Sun travels in a southerly arc so the north side of a house will get no direct sunlight. This is why it is said, somewhat correctly, that moss grows on the north side of a tree. So the shadow of the moon like the shadow of the top of a tree will move from west to east as the moon, moving slower than the rotation of the Earth, casts a shadow. Well, it seems clear to me now. I think even Gilligan could get it.

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