The world should revolve around me

by Alicia
(Sydney, Australia)

I'm doing a maths investigation at the moment and I'm looking at how the speed of one complete rotation around the sun differs for each planet. I was wondering if you would be able to give me the formula in which you need figure this out?

Barry's Response - Good question, Alicia:

It depends on what you already know about them. If you have the planet's year length, in days for instance, and the average distance from the sun, in km. It would go something like this.

Speed = (approximately) pi (3.1415926) x distance from the sun (kilometres) x 2 divided by the number of days.

This will give a pretty good estimate in km per day. Divide by 24 for km per hour OR 86400 to get km per second. If you prefer miles, you can then divide the result by 1.609

It becomes more complicated if you consider the fact that these orbits are not perfect circles. But you probably don't need to worry about that for this exercise. This method gives a good estimate for average speed.

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