The period of the Earth's rotation is constant at any point on its surface, but the same cannot be said for the speed of rotation. Consider an observer at the equator, where the circumference to be traveled in one day is 40070 km. If we approximate the length of the day to be 24 hours, we can calculate the speed at the equator using the formula speed=distance to travel/time. At this point we get a speed of 1670 km/h.
If we move the latitude and imagine that we are at 45° (at the height of Piedmont), the circumference that we have to travel each day is less and consequently the speed at which we move is also less, which is 1180 km/hour.
The speed of rotation decreases as we move towards the North Pole (or, similarly, the South Pole). Of the observatories located at these two points, they are in fact characterized by zero rotation speed.
In addition to rotating on itself, the Earth then moves around the Sun at a constant speed for any observer on the surface. Knowing the semi-major axis of the orbit, one can calculate the circumference of the orbit that our planet travels each year, and dividing this by the duration of the year, one finally obtains the orbital velocity: 107,000 km/h. In one year, the Earth travels 940 million km around the Sun!
The Earth then orbits around the center of the Milky Way, along with all the other objects in the solar system. The Sun, and with it the Earth, moves within our Galaxy at the impressive speed of 200 km/s. Still, it takes us 230 million years to make a complete circle around the center of the Milky Way.
The Milky Way itself, however, is not motionless, and it too, with everything in it, is moving through space toward other galaxies. In particular, the Milky Way is moving toward the Andromeda galaxy at a speed of 112 km/s. The two galaxies will collide and merge in about 4 billion years.
Credits: NASA, JPL, LRO.
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