Sun and Earth

[Brugel]

If all motion is relative then is it just as valid to maintain that the sun goes round the earth as it is to maintain that the earth goes round the sun?

[Loosehead]

Not really with an object as massive as the sun the effect the Earth has is negligable. It does cause a "wobble" however and it's one of the ways that planet spotters detect planets around other stars.

Ok imagine you are in the garden and you swing a small child around. Now the child does cause you to wobble a bit but you wouldn't say you are orbiting the child now repace the child with say a ping pong ball. Although the ball is exerting a tiny force on you it's not noticable. The sun and the earth are in similar proportion mass wise to you and the ping pong ball ie no noticable effect so to answer you question, no.

[landie]

Does it make a difference to your daily life is what you need to ask.

Does day follow night or night follow day?

[Space]

It makes a difference if you try to calculate the planet's movements.
Most of the time, you will want to be in an inertial frame of reference to make your calculations.
Neither earth nor sun 's frames of reference are strictly inertial, but the sun's frame of reference is a better approximation because it doesnt wobble as much as earth's. So it will give more accurate results.

[landie]

Oh, I'm sorry. You thought I was being serious.

[petsim]

Both the Earth and the Sun rotate around a common point. That point happens to be within the circumference of the Sun.

[petsim]

Sorry, hit submit too early. The common point is the centre of gravity of the 2 masses.

[bernardo]

They rotate around the common centre of mass.  The sun is so much more massive than the Earth that the common centre of mass is nearly where the sun is anyway.  But yes, we could imagine the Earth as being fixed and the Sun as going around the Earth, but to do so would make it more difficult to calculate the orbits of all the other planets and moons.  We consider (or imagine) the Sun to be in a fixed point because it makes the calculations easier.  In reality, the Sun is moving around throught he galaxy anyway, and is taking all the planets and moons along with it.

[Hamish]

Yes, However it makes everything else very complicated to work out and describe therefore it is more convenient to think of it as the earth going round the sun. ie it is sensible to chose a frame of referance (a stationary point, relative to the sun, above the solar disk for example) which allowes the simplest description of all the motions of the planets. In this case they would all be described as orbiting the sun in aproximately circular orbits.

[Brugel]

Thanks to everyone who replied. I've a feeling I once saw an extract from a book written by Einstein himself in which he said that there is no contradiction in taking the view that the sun goes round the earth. But I can't be certain.