h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

due to the convo on the dawkins thread at the moment, they are discussing the earth going round the sun and frames of reference

question

IF the sun went round the earth(all sizes and distances the same)

how fast would it be moving???

same as the Earth is going round the Sun

no!!!

because the earth does one orbit at a distance of 1AU in 365.25 days

the sun would have to do the same distance in 24 hours!!!!

The Sun does go around the Earth. They are in binary orbit. It's just that the relative mass of the Sun is so huge that it moves very little compared to the Earth.

None of Post 3 makes the slightest sense to me.

B

Take a sidereal year of 365.242
Take Earth's mean orbital velocity in km/h of 107,218
Multiplying those together you get an orbital velocity for Sol in a geocentric orbit of 39,160,561.756 km/h

Which is about 15 times faster than any hypervelocity star yet observed. About 1/28th the speed of light.

thank you jack

A bit of a stretch, MB. I'm pretty sure the centre of gravity of the Earth/Sun system is within the sun. Hardly a binary orbit.

plus all the other binary orbits in the solar system, just gives the sun a wobble

You could say that the earth is spinning on its axis once a day and the sun is going around it once every year; or you could say that the earth is fixed, and all the rest of the universe rotates around it once a day. This is the view that Ptolemy, in the absence of any evidence either way, took, as he reasoned that things in the sky must be very light since they didn't fall to the ground. So it should be easier for them to move at speed, than for the whole earth, which he knew was very heavy, to move.