# Why does the moon move faster across the sky than sun?

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#1
I came across a question putting the sun, moon and stars in the order of slwoest to fastest in terms of their movement across the sky. I thought that if something is closer to you then it will seem to move across the sky quicker. I put 2 pens in front of me and then just simply rotated my head and the pen closer to me appeared to move across my vision quicker and that pen was the moon as the moon is closer than the sun. Thanks for answering in advance
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6 years ago
#2
Not exactly sure but perhaps because, we are moving around the sun. Yet the moon moves around us as we rotate. Perhaps the two motions together, of us rotating and it orbiting us, makes it appear to move faster.

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6 years ago
#3
The moon orbits the earth once every 27 days.

The earth orbits the sun once every 365 days.

Therefore the position of the moon relative to the sun will appear to cross the sky around 13.5 times faster than the sun. (365/27 = 13.5)
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6 years ago
#4
(Original post by dont-have-a-name)
I came across a question putting the sun, moon and stars in the order of slwoest to fastest in terms of their movement across the sky. I thought that if something is closer to you then it will seem to move across the sky quicker. I put 2 pens in front of me and then just simply rotated my head and the pen closer to me appeared to move across my vision quicker and that pen was the moon as the moon is closer than the sun. Thanks for answering in advance
I'm a bit confused? So in your results from your mini pen experiment matched with your initial thoughts didn't they? Doesn't that kind of explain it.

But it's all relative. We are orbiting the sun whilst rotating and the moon is orbiting us.
If both we and the moon were not orbiting, everything will be still (in terms of orbiting) and everything will look the same. The fact we rotate just means that everything( the moon and sun) will move across the sky at the same pace.
But since we are orbiting the Sun slower (in terms of angle/longer period) than the moon is orbiting us, I guess this is the reason why the moon would move quicker across the sky than the sun.
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6 years ago
#5
(Original post by uberteknik)
The moon orbits the earth once every 27 days.

The earth orbits the sun once every 365 days.

Therefore the position of the moon relative to the sun will appear to cross the sky around 13.5 times faster than the sun. (365/27 = 13.5)
But you're assuming that the rotation of the earth has no effect on this? The sun appears to orbit the earth once every day when seen from the equator doesn't it?

(Original post by Foo.mp3)
The rate at which the sun appears to move across the sky is a function of the earth's rotation. The rate at which the moon appears to move across the sky is a function of the same plus the non-stationary orbit of the moon around the earth (a positive addition as the moon orbits the earth in the same direction as the earth rotates [counter-clockwise if you take the north pole as the top of the earth]
When the moon is orbiting in the same direction as the earth rotates then it should be a subtraction shouldn't it?

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6 years ago
#6
(Original post by RoyalBlue7)
But you're assuming that the rotation of the earth has no effect on this? The sun appears to orbit the earth once every day when seen from the equator doesn't it?

When the moon is orbiting in the same direction as the earth rotates then it should be a subtraction shouldn't it?

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The problem is indeed one of interpretation.

The OP made a general statement which left more questions than answers."I came across a question putting the sun, moon and stars in the order of slowest to fastest in terms of their movement across the sky."

b) is this referring to the observation during a single day or over a many years?
c) is the observation made wrt the sun and the moon during an eclipse?
d) is the observation made wrt the rising and setting times of the sun, moon and stars etc?

We are all making assumptions and breaking the primary rule of physics - no assumptions.

So the request to the OP should be: can you please provide more information on the context for this question. Without it any answer will be through assumption and based on individual interpretation which will be different for different observers.
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6 years ago
#7
(Original post by uberteknik)
..
Fair enough. Yes, there has to be more information before an explanation could be thought up

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3 years ago
#8
The explanations is the earth being flat, motionless, and all outer body's revolve around us,It all works when we make the sun small and local like our moon, it takes 365 days for the sun to do a full annual orbit above earth doing a circle motion from north equator to south eqauter and back, while taking a circle rotation of earth every 24hours, this would explain the still moon and all other bodys,,, as no sphere is rotating, to my knowledge a gaint planet like Jupiter would rotate slower than earth but it only takes 9 hours , therefore it isnt a sphere rotating alone , but is a object rotating according to what and how the firmament is rotating around us, clealry we will only see the same face of Jupiter and that same face does a full rotation of earth in 9 hours, therefore everything is moving around us and we are still motionless God is great
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1 year ago
#9
Correct
Last edited by Jusdan; 1 year ago
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