Why does the sun appear to move eastwards from Earth?

Click For Summary
SUMMARY

The apparent eastward movement of the sun is a result of Earth's anticlockwise rotation, which causes the sun to rise in the east and set in the west. Observers can detect this eastward motion by noting the sun's position against the background constellations, which shifts slightly each day. The misconception that the sun moves westward is clarified by understanding that the sun's position changes relative to the stars, not due to its own motion. The Earth's rotation and revolution around the sun are conventionally described from a north pole perspective, reinforcing the anticlockwise motion.

PREREQUISITES
  • Understanding of Earth's rotation and revolution
  • Familiarity with celestial navigation concepts
  • Basic knowledge of astronomy terminology
  • Awareness of perspective in observational astronomy
NEXT STEPS
  • Research the concept of celestial mechanics and how it affects the perception of celestial bodies
  • Study the movement of stars and planets using tools like Stellarium or SkySafari
  • Learn about the Earth's axial tilt and its impact on seasons
  • Explore the differences between geocentric and heliocentric models of the solar system
USEFUL FOR

Astronomy enthusiasts, students learning about celestial mechanics, educators teaching astronomy concepts, and anyone interested in understanding the dynamics of Earth's motion relative to the sun and stars.

amenhotep
Messages
29
Reaction score
1
Hello,
I've been reading astronomy books for some time now but after leaving things for a while I seem to forget rotation directions.
For example, I know that the Earth spins in the anticlockwise direction. That is easy to see why. They say that motion of the Earth is eastwards. Because of the eastward motion of earth, the sun appears to move westwards from Earth. This means that we can verify this motion by noting that the sun first appears in the east, rises and dips in the west.
Also, the Earth revolves around the sun in an anticlockwise manner. The sun is said to move eastwards with respect to the background constellations when viewed from Earth. So, here are my questions:
1. What does "the sun appears to be moving eastwards" mean? By that, I mean, how can I detect this eastward movement by observing the sky? Is the eastward movement of the sun analogous to the sun's changing altitude in the sky at a given time of the day?
2. Because the Earth spins anticlockwise, the sun appears to move westward. Similarly, the Earth revolves anticlockwise around the sun. By the same token, why doesn't the sun appear to move westward ? If the sun was actually moving westward, what difference would that make ? Is it just reversal of seasons. Like, instead of Spring, Summer, Autumn and Winter, it will be Spring, Winter and Autumn and Summer.

I am learning astronomy purely from textbooks and as you can see I do not have a grasp of the concept of relative motion. I think I might be confusing clockwise motion with westward motion and anticlockwise motion with eastward motion.

Please feel free in being verbose in your answers. There might be many things that I don't fully grasp.

Thanks
 
Astronomy news on Phys.org
amenhotep said:
... I know that the Earth spins in the anticlockwise direction.

A remarkable thing to know, since it isn't true. The spin direction of the Earth is purely dependent on where you are. If you are above the North pole, then it is counterclockwise and if you are above the South Pole, it's clockwise.

EDIT: And in response to your recent post which you apparently deleted, if you are at the sun, you get to choose which way you care to state it since it is neither.
 
Last edited:
amenhotep said:
2. Because the Earth spins anticlockwise, the sun appears to move westward. Similarly, the Earth revolves anticlockwise around the sun. By the same token, why doesn't the sun appear to move westward ?
again not factual ... it depends on your perspective ( see Phinds's response)
 
amenhotep said:
1. What does "the sun appears to be moving eastwards" mean? By that, I mean, how can I detect this eastward movement by observing the sky? Is the eastward movement of the sun analogous to the sun's changing altitude in the sky at a given time of the day?

No, it is the movement of the Sun against the background stars. You can see this by watching the stars in the East every morning just before the Sun rises. Each day the Sun is a little further easterly in the constellations.

amenhotep said:
2. Because the Earth spins anticlockwise, the sun appears to move westward. Similarly, the Earth revolves anticlockwise around the sun. By the same token, why doesn't the sun appear to move westward ? If the sun was actually moving westward, what difference would that make ? Is it just reversal of seasons. Like, instead of Spring, Summer, Autumn and Winter, it will be Spring, Winter and Autumn and Summer.

The seasons would still be in the same order. The coldest part of the year occurs when the north hemisphere is tilted away from the Sun, Spring is next, then Summer then Fall. It makes no difference whether we are orbiting the Sun clockwise or anti-clockwise.
 
phinds said:
A remarkable thing to know, since it isn't true. The spin direction of the Earth is purely dependent on where you are. If you are above the North pole, then it is counterclockwise and if you are above the South Pole, it's clockwise.

Not true? I believe the standard convention is to describe the spin of the Earth and its revolution around the Sun as viewed from the North Pole.
 
Drakkith said:
Not true? I believe the standard convention is to describe the spin of the Earth and its revolution around the Sun as viewed from the North Pole.
Is it? I was not aware of that, but if it is then his statement was reasonable. I see that davenn agreed w/ me. I still think that as a bald, stand-alone statement, it's a bad idea, and if it's a convention, it's a bad one.
 

Similar threads

  • · Replies 17 ·
Replies
17
Views
3K
  • · Replies 7 ·
Replies
7
Views
6K
  • · Replies 2 ·
Replies
2
Views
11K
  • · Replies 10 ·
Replies
10
Views
4K
  • · Replies 56 ·
2
Replies
56
Views
6K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 142 ·
5
Replies
142
Views
135K
Replies
4
Views
3K
  • · Replies 8 ·
Replies
8
Views
5K
  • · Replies 6 ·
Replies
6
Views
4K