Imagine yourself on a warm summer's day, lying on a soft grass meadow next to a beautiful tree, looking up at the blue sky. The air smells good and, except for a few chirping birds, it's quiet. You are relaxing, not moving. Your body is as still as it can be. Are you really not moving? Is it ever possible to really stand still?We live on the surface of a nearly round world that spins around its axis, or center of rotation, about once every 24 hours. The distance all the way around the Earth, its circumference, is about 25,000 miles. Therefore, we (at least people on the Earth's equator) are spinning at speed of about 25,000 miles divided by 24 hours, or about 1,042 miles per hour. Not exactly standing still!
In addition to spinning around its own center, the Earth, as the third of nine planets in our solar system, travels in a long, almost circular orbit around the Sun. It takes one year to go all the way around once. To estimate the distance the Earth travels in a year we can use the formula for the circumference of a circle, 2(pi)R, with "R" (the radius) being the distance between the Earth and Sun - approximately 93 million miles. The distance all the way around turns out to be about 584 million miles. The Earth travels this path in about 365 days, or 8,760 hours. Therefore, the speed of the Earth, and all of us on it, as we race around the Sun is about 67,000 miles per hour. Pretty fast for standing still!
Our Sun is near the edge of one of the spiral arms that unwinds from the center of our galaxy, the Milky Way. It is one of hundreds of billions of other suns (stars) in the Milky Way galaxy. Our galaxy is disk shaped, almost circular, and is about 100,000 light years across (its diameter). We are located about 3/5 of the way out from the center, about 30,000 light years. The entire galaxy spins around its center about once every 250 million years. Therefore, we are moving around the galactic nucleus at a very approximate rate of 188,000 light years divided by 250 million years. This turns out to be an hourly speed of about one-half million miles per hour. Definitely moving!
So why don't we feel like we are moving? Because motion is felt relative to the predominant local source of gravity and relative to local surroundings. Our predominant local source of gravity, the Earth, is moving with us. In fact we are riding it on our high speed trip through the universe. Our local surroundings, the air and objects around us, are all moving with the Earth. We don't feel our cosmic movement because most of what we see and touch is coming along for the wild ride. The only way we become aware of our movement is by looking beyond our local surroundings - to the Sun, planets, stars and galaxies.
Is it possible to stand still? Unfortunately, or fortunately, it is something no one on Earth can ever do.
Back to Star Facts Home Page
Send suggestions, astronomy tips, corrections or comments to Pete Harris
via e-mail at odyssey@ccnet.com. Pete is also the creator of the website
The Child
Abuse Prevention Council of Contra Costa County