# Speed of the umbra during eclipse vs rate of the Earth's rotation

• I
• imsmooth
imsmooth
The earth rotates faster than the moon orbits. Thus, the moon appears to move from East to West each day. The shadow of the moon during an eclipse as it moves along the curved earth makes it move faster and we see it move West to East.

My question is If a solar eclipse happens near noon and one is directly under the sun-moon alignment, wouldn't the shadow move East to West for a brief moment since the earth rotation is faster at this point? Or is it never faster?

It is never faster. The Earth spin makes the equator move about 500 m/s. The Moon’s orbital speed is about 1 km/s.

FactChecker
To add to that, it is easy to draw this conclusion knowing only the distance to the Moon (ca 384000 km), the radius of the Earth (ca 6300 km) and the periods (28 days and 1 day). As 6300x28 is about 180000, the corresponding equator speed is about half of the Moon’s orbital speed.

Thank you. I should have done the calculation first.

• Astronomy and Astrophysics
Replies
10
Views
2K
• Astronomy and Astrophysics
Replies
3
Views
2K
• Astronomy and Astrophysics
Replies
3
Views
944
• Astronomy and Astrophysics
Replies
8
Views
2K
• Introductory Physics Homework Help
Replies
5
Views
1K
• Astronomy and Astrophysics
Replies
16
Views
2K
• Astronomy and Astrophysics
Replies
17
Views
2K
• Astronomy and Astrophysics
Replies
2
Views
2K
• Astronomy and Astrophysics
Replies
1
Views
4K
• Astronomy and Astrophysics
Replies
20
Views
3K