Thursday, September 25, 2014

The grand carousel that actually goes somewhere

When I was a kid, I didn't watch the sun very closely. I saw it rise, and I saw it set and that was enough for me. Oh, sure, I was into astronomy, could tell you the names of all the planets and could tell you some of their orbital periods, their masses, and their order from nearest to the farthest from the sun. Pluto is still a planet. I don't care what anyone else says. There were nine planets when I was a kid, there will still be nine planets in my mind today.

I also learned about how the earth has an axis of rotation that is tilted 23 degrees from the plane of its orbit. This tilt of the earth gives rise to the seasons as we all orbit the sun. The seasons become more noticeable as we move away from the equator, the midpoint of the earth between the poles. But at the poles, the biggest difference we see in the seasons is the complete disappearance of the sun during the winter. Winter at the poles is a very long night, indeed.

I see the sunrise against the mountains, day in and day out. As I gained more experience, I found that it helps to have a point of reference on the horizon. As the weeks pass, I see the sun march back and forth across the horizon at sunrise and sunset. During the early morning and afternoon hours, I note the shift in the reflection of light off buildings and cars over time. We are, it seems, in motion on a grand carousel.

The earth spins at what may seem to be an incredible speed. As Einstein pointed out, speed is relative, so we don't feel it as motion because we're moving with it. Relative to the axis of rotation, though, people at the equator are moving at about 1,070 miles per hour. That speed decreases as you get closer to the poles where you are just spinning rather than experiencing any lateral motion.

In turn, the earth rotates around the sun. Every year, the earth travels 584 million miles around the sun. A year may seem like a long time, but the earth is still traveling very fast by our own standards - at a speed of approximately 67,108 miles per hour, or about 18 miles per second. That's a pretty heady speed, relatively speaking, but since we're moving with the earth, we don't really feel it now, do we?

The sun is a small, mediocre star in a galaxy of 100 to 400 billion stars - the actual number of stars is not really known since we can't see all of the stars in our galaxy. Our galaxy, affectionately known as The Milky Way, is about 100,000 light years across. To put that in perspective, the nearest star to our star is about 4 light years away. One light year is the distance covered by light in a year, or about 5,878,499,810,000 miles. That's 5.8 quadrillion miles. 

Based on a distance of 30,000 light years and a speed of 136 miles per second, the Sun's orbit period around the center of the Milky Way is about 225 million years. That period of time is called a cosmic year. The Sun has orbited the galaxy, more than 20 times during its 5 billion year lifetime. That makes the sun about 20 cosmic years old.

The Milky Way doesn't really orbit anything else, but it is part of what we know as The Local Group. This is a small group of galaxies that orbit around the Milky Way and the Andromeda Galaxy. If anything, the Milky Way is definite going somewhere - towards something called the Shapely Supercluster of galaxies comprising some 74,000 galaxies. The estimated speed of motion of the Milky Way towards that super cluster? About 1.4 million miles per hour.

Dean Martin is not so famously quoted as saying, "You know you're not drunk if you can lay on the floor without holding on." On the other hand, David Byrne says that "the world moves moves on a woman's hips, the world moves as it swivels and bops". Lucky for us, it's all relative so we can still enjoy a great game of billiards. In the meantime, we can relax because the passing of the seasons on the Grand Carousel is something we can all share, on any scale, even if we're actually going somewhere.
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