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What does eastward mean ?

  1. Nov 18, 2014 #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
     
  2. jcsd
  3. Nov 18, 2014 #2

    phinds

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    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: Nov 18, 2014
  4. Nov 18, 2014 #3

    davenn

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    again not factual ... it depends on your perspective ( see Phinds's response)
     
  5. Nov 19, 2014 #4

    Drakkith

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    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.

    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.
     
  6. Nov 19, 2014 #5

    Drakkith

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    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.
     
  7. Nov 19, 2014 #6

    phinds

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    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.
     
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