# Thread: If a day is one full rotation of the earth...

1. Member
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## If a day is one full rotation of the earth...

...how is it that daylight only shifts by 5 hours or so throughout the year? If the sun is directly overhead at 12PM in June, then shouldn't the sun be on the exact opposite side of the earth at 12PM in January?

[image="http://www.physics.uwo.ca/everyday-physics/images/earth-orbit.gif"]

2. there is a measurement for the day that takes that into account. I forget what it's called (Sidereal Day?). But the Solar Day, the day we use in our lives most often, is counted roughly relative to the position of the sun, so we don't have 12PM shifting between Noon and sunrise and midnight all year.

3. Order of Kilopi
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Yep, the Earth actually turns through about 361&#186; each day: a full turn, then an extra degree to catch up with the amount the Sun has shifted in the sky as the Earth moves along its orbit. That's a "solar day" of 24 hours.
A single turn of 360&#186; is called a "sidereal day", and it takes a little less than 24 hours.

Grant Hutchison

4. Originally Posted by grant hutchison
Yep, the Earth actually turns through about 361º each day: a full turn, then an extra degree to catch up with the amount the Sun has shifted in the sky as the Earth moves along its orbit. That's a "solar day" of 24 hours.
A single turn of 360º is called a "sidereal day", and it takes a little less than 24 hours.

Grant Hutchison
I got it right! w00t!

5. Member
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Excellent! So, the only really thing left to cause the apparent change in dawn/dusk is the tilt of the earth?

6. Originally Posted by Utwo
Excellent! So, the only really thing left to cause the apparent change in dawn/dusk is the tilt of the earth?
The varying length of the solar day is due to both the eccentricity of the Earth's orbit (i.e., the Earth moves faster when it is nearest the Sun and slower when it is farthest from the Sun) and the axial tilt of the Earth.

http://www.astronomynotes.com/nakedeye/s9.htm

Dave Mitsky

7. hey, Shaggy One..
love the avatar...
ever been Rejected?

hey, Shaggy One..
love the avatar...
ever been Rejected?
Constantly.

9. Member
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My ANUS is BLEEDING

10. Originally Posted by UTwo
My ANUS is BLEEDING
You should get that checked out.

In terms of rotation of the earth, a day is actually 23 hours 56 minutes and a few seconds. The difference between this and the 24 hour solar day results in there actually being 366 1/4 rotations of the earth in a year, while the sun only passes overhead 365 1/4 times.

11. Member
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Does the moon revolve about the earth's equator, such that its orbit is also 23 degrees away from the plane of the solar system?

12. The Moon's orbit is tilted by just over 5 degrees from the ecliptic. So it follows the path of the Sun pretty closely, and a full Moon is high in the sky in winter and low in summer.

BTW what is the meaning of your previous post? Or maybe I'd rather not know?

Fred

13. Member
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Originally Posted by Nowhere Man
The Moon's orbit is tilted by just over 5 degrees from the ecliptic. So it follows the path of the Sun pretty closely, and a full Moon is high in the sky in winter and low in summer.

BTW what is the meaning of your previous post? Or maybe I'd rather not know?

Fred
Hehehe. It has to do with Shaggy's icon. It's a line from an animated short called Rejected, which is hilarious. I'll see if I can find it online somewhere, and if it doesn't violate any copyright laws, I'll send you a link.

14. Originally Posted by Utwo
Hehehe. It has to do with Shaggy's icon. It's a line from an animated short called Rejected, which is hilarious. I'll see if I can find it online somewhere, and if it doesn't violate any copyright laws, I'll send you a link.
Links aren't a problem, dropping an image link is probably not a good thing.

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