Is the earth drifting away from the Sun?

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Curiosity Science Physics Is the earth drifting away from the Sun?

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  • Today is my over-thinking day! Sorry for such a basic question! Is the earth really getting farther from Sun?

  • I’m not sure about your question. If you are asking about the position of Earth right now, the answer is both. Earth’s orbit is elliptical. So the earth moves closer to the sun at its orbit’s perihelion (closest point) and away from sun at the aphelion(farthest point). Right now, the earth is approaching towards its aphelion.

    Earth is about 147.1 million kilometers from the Sun at perihelion in early January, in contrast to about 152.1 million kilometers at aphelion in early July.

    If your question is about the orbital drift, the answer is yes, the earth is getting away from sun, but very slowly. At the sun’s core, the nuclear fusion is constantly converting the mass of the sun into energy. As this happens over a period of time, the sun will lose mass and eventually affect the earth’s orbit by expanding it. A rough estimate is around 1.5 to 2cm per year.

    • I was asking about the orbit part. Sorry! I should have mentioned that! So what is the case with the moon then? Is the Sun’s nuclear fusion affecting the moon’s orbit too?

    • If the earth’s orbit is affected, then the moon’s orbit will be affected too. Moon is actually drifting away at 3.8 cm per year rate. This is however due to the tidal effects on the earth due to moon’s gravity. Such effects causes earth to bulge at its surface (causing tides) on both ends. But as the earth has larger water and it rotates faster than the moon, the bulge recedes a little compared to the crust. The water mass then exerts a pull on the moon and accelerates it. The moon now steals the earth’s energy and angular momentum here and goes to a slightly higher orbit. The moon’s gravity in turn pulls on the bulge and creates a friction to slow down the earth’s rotation. If you further read about the tidal forces between Earth, Moon and Sun and you will understand this better. This will be a good start.

    • I get it all, except the part where you mentioned about the Moon stealing the angular momentum! I don’t get it. How can moon steal gain energy and angular momentum? I do understand that the angular momentum should be conserved. But how?

    • Appreciate your question! Earth’s rotation is slowing down. I hope you get this part. Now think about this. If the earth slows down, where would the angular momentum of the earth go? Of course, to the massive object that is being pulled towards the earth. There it is! The angular momentum gets added to the moon by the acceleration due to the impulse (pull) the moon experiences.

    • Adding to @dr_cave’s explanation, you should note that the bulge isn’t literally a bulge in water mass. In fact, the bulge is created due to the squeezing of the two other perpendicular spots on the surface of the Earth.

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