How did scientists determine how fast earth's orbit is around the sun?
The orbital speed of the Earth is easy to calculate using geometry - we can find the circumference (distance) and divide it by a year (time)
The Earth completes one full orbit,
The Earth's orbit is slightly elliptical, but is pretty close to circular. The mean (semi-major) distance from the sun to Earth is 149.6 million km. Remembering our geometry a circle with a radius of 149.6 million km is:
940 million km.
the orbital speed can be calculated using: