Question

Could one calculate the relative speed of the Sun viewed from the Earth?

Answer 1

The average distance of the Earth from the Sun is spproximately 150 million km or 1.5×1011m

The orbit of the Earth around the sun is roughly circular (more eliptical really, but let's keep it simple), with a period of roughly 365 days.

So the path that the Earth traverses in 365 days is approximately the circumference of a circle of radius 1.5×1011m.

Use the formula C=2πr to find that this is about 9.4×1011m.

The number of seconds in 365 days is:

365⋅24⋅60⋅60=31536000

So the tangential velocity of the Earth is approximately:

9.4×10113.1536×107≈3×104ms−1
That is 30 km per second.

I hope it helps you.