QUESTION:

Hi,

I’m thinking about being an astronomer when I get older, so right now, I’m researching on my own about space, planets and moons etc. This might be a stupid question but I’ll ask anyway. I found out that Saturn’s moons travel the fastest at 932 miles per hour. How fast does Earth’s Moon travel? What about the rest of the planets?

Thank you,

Meggy

REPLY:

Hi Meggy,

Well, astronomy as a profession is certainly looking up (Ha, ha). Seriously, that’s great, and don’t let my terrible humor turn you off.

As for your question, about the Moon: Well, the Moon travels around the earth in a slightly elliptical orbit, so its orbital speed varies depending on whether it is at the point closest to the earth (Perigee) or farthest away (apogee). The Mean orbital speed of the Moon is 0.635 miles per second. When it is closest to Earth, the Moon’s orbital speed is 0.67 miles per second. When it is farthest from Earth, the Moon’s orbital speed is 0.60 miles per second. Of course the Moon orbits the earth, which orbits the Sun (see below)

The planets follow the same rule of orbital speed: the closer a planet is to the Sun, the faster it orbits the Sun. Here’s a list of the planets (in decreasing order from the Sun) with their average orbital speeds:

Mercury: 29.4 miles per second
Venus: 21.8 miles per second
Earth: 18.8 miles per second
Mars: 15.0 miles per second
Jupiter: 8.1 miles per second
Saturn: 6.0 miles per second
Uranus: 4.2 miles per second
Neptune: 3.4 miles per second
Pluto: 2.9 miles per second

Notice the big jump in orbital speed between Mars and Jupiter. That’s because there’s a wide belt of asteroids (minor planets) that lies between the two planets.

Hope this helps!
Steve O’Meara

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