Speed is relative. We know how far the Earth is from the Sun, and we know that it takes one year to make a complete circuit. We also know that speed equals distance divided by time, so by dividing the calculated circumference (in kilometers) by the number of hours in a year, we get our speed around the Sun: 107,225 kph (66,630 mph).

However, the sun is also traveling in its orbit around the center of the galaxy. To orbit the sun, we travel a little faster in January (perihelion) and a little slower in July (aphelion). This is called perihelion and it’s the point in the orbit of a planet where it is nearest to the Sun. It’s opposite is called aphelion, which is the point where the orbit of the object is farthest from the Sun. Since equal areas must be covered in equal intervals of time, the planet’s orbit speed has to be the fastest at perihelion and slowest at aphelion.

The Earth averages a speed of 782,460 kph (486,220 mph) relative to the center of our galaxy. That’s not the end of the story, either, because the galaxy is traveling through space, at a speed greater than our orbit around the center of the galaxy:1,987,200 kph (1,234,840 mph). Almost makes you dizzy, doesn’t it?


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