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Q & A: Sun putting on some weight

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Most recent answer: 10/22/2007
Q:
If the sun became twice as massive as it is today, would it affect our weight on earth?
- Shannon Lee (age 19)
Enverga University, Philippines
A:
Short answer: no.

We're in free-fall around the sun -- we're "weightless" as an astronaut is in orbit around the Earth. In fact, the only reason we have weight is because the Earth is pushing against our feet with electromagnetic forces, to counteract the gravitational forces pulling down (Newtonian picture). The gravitational force the Sun exerts on us is almost exactly what's required to keep us in an almost circular orbit around the sun. Double the mass of the sun and you change our orbit around the sun, but not the interaction between yourself and the Earth.

But -- something does change a bit! The tides which are due partly by the sun and partly by the moon would change in strength -- the sun's component would double. This effect has a tiny tiny effect on your weight. If the sun's mass were to double without pushing or pulling on the Earth, then the Earth's orbit will change to an ellipse which brings it out to our current radius but spends most of its time closer to the sun. The tides would probably get even stronger then, particularly when our orbit takes us closer to the sun.

Tom

(published on 10/22/2007)

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