Imagine Home  |   Ask an Astrophysicist  |

## The Question

(Submitted October 28, 1997)

How fast does the Earth move around the Sun? Why, when the Earth moves at such a high rate of speed, don't we feel it?

Earth's average distance to the Sun is 150,000,000 km (93 million miles), therefore the distance it travels as it circles the Sun in one year is that radius x 2 x pi, or 942,000,000 million kilometers in a year of 24 hours/day x 365 1/4 = 8,766 hours so you divide to get 107,000 km/h or about 67,000 mph.

You could also say the Earth moves around the Sun at 30 km/s. The Sun circles the center of our Galaxy at about 250 km/s. Our Galaxy is moving relative to the 'average velocity of the Universe' at 600 km/second ( http://antwrp.gsfc.nasa.gov/apod/ap960205.html)

As to why you can't feel this speed: it's because you have no 'speed organs' which can sense absolute speed, you can only tell how fast you are going relative to something else, and you can sense changes in velocity (accelerations). Scientists have no instruments which can sense absolute speed either, and so they deny that the concept of absolute speed has any meaning.

Suppose you are in a car traveling down the road. How can you tell how fast you are going? The speedometer tells you how fast your wheels are turning, but you could be standing dead still, spinning your wheels trying to get off a patch of ice, so put black tape over the speedometer. The car vibrates because it's working so hard, not necessarily because it's moving, so get a solidly built car that doesn't vibrate, and use a vibration absorbing seat cushion so you can't feel anything. The air whips noisily past your window as you drive through it, or maybe you're sitting still in a windstorm (was that a cow flying by?), use earplugs so that doesn't distract you. Outside you can see the scenery whizzing by, but it's actually a rear-projection screen that 'they' are showing moving images on to confuse you. Don't believe it--paint the windows black.

OK, now, how fast are you going? You have no way to tell. You don't feel like you're moving. You feel just as you would if you were standing still!

Now scrape off the paint off your windows before you run into a tree (or a tree runs into you).

David Palmer
for Ask an Astrophysicist

##### Questions on this topic are no longer responded to by the "Ask an Astrophysicist" service. See http://imagine.gsfc.nasa.gov/docs/ask_astro/ask_an_astronomer.html for help on other astronomy Q&A services.

 Prev Main Next