Super strands of galaxies
Copyright ©2014 by Ralph Couey
This calendrical thing we call "a year" is, of course, the calculation of the time it takes for the Earth to complete on lap (or orbit, if you prefer) around our star. That's 365 days, measured as a fraction over 24 hours, the time it takes for the Earth itself to make a complete spin on its axis. Those days are broken into 12 months which at first were established according to the phases of the moon. Nearly everyone knows this.
I was thinking the other day (admittedly a hazardous undertaking) about time and space and a question occurred to me.
How do we really know we've made the lap?
If I'm going to take my dog Tweeter for a walk around the block, I have a fixed point for starting and ending. But space has no fixed reference point because everything is in motion.
The Earth orbits the sun, which in turn orbits the center of the Milky Way galaxy. The Galaxy moves in a complex gravitational dance with other galaxies within the local group. The local group, arrayed as part of a larger strand and superstrand of thousands of other galaxies moves in response to their interactive gravitational fields. And the whole ball of wax continues to expand outward from that mysterious point in space and time where the Big Bang brought it all into existence. Here on the surface of this planet, reference points on land are fixed and recognizable. (Yes, I know the continents are drifting around on the mantle, but let's not megger this thing up any worse, okay?)
So if there are no reference points, how do we know we've made that circle? There's no finish line, and since the sun's surface is a constantly changing oatmeal-looking mass of incandescent gas and magnetic fields, no one can point to a place that might be used as a start/finish line. It would seem that trying to determine a finish line in space would be like trying to find your car in a shopping mall parking lot while someone is driving it around. The only clue really are the cycle of the seasons.
As earth orbits the sun, tilted at it's 23.5 degrees, the angle of the sun's rays changes. In the northern hemisphere winter, Earth is closer to the sun. But with the surface tilted away, the suns rays, and therefore heat, hit the surface at a shallow angle. During northern hemisphere summer, the Earth is at the far point of its orbit, but the surface is tilted towards the sun, its rays hitting the surface at a more direct angle. That makes things warmer. We cycle through four seasons, one hot, one cold, and two in-between, and somebody has decided that such a cycle constitutes a year.
Thanks primarily to the Moon, Earth's tilt is stable, not shifting by more than 5 degrees in the last 130 million years, so this cycle will likely not change, at least as long as humans can be reasonably expected to inhabit this planet.
To determine how fast we move, you have to add up a lot of velocities. I won't bore you with the process, but according to some science-oriented websites, in the 365 days it takes for the Earth to make it's one lap around the sun, the entire solar system has traveled some 23.6 billion miles through space.
You could become the office nerd with this knowledge. When a colleague returns from two weeks of vacation and you ask, "Where did you go?" and they answer, "Nowhere. Just stayed around home." you could quickly point out that in actuality that during that two-week time span, they actually traveled some 909.6 million miles. And then end up eating lunch by yourself, wondering why everyone now calls you "Sheldon."
This isn't really useful or practical knowledge. It's not going to pay the mortgage, or file your tax return, or return the DVD back to the Red Box. Some might even term such contemplation a waste of time. However, I contend that such contemplation of the larger universe helps to put a lot of things in perspective, not the least of which is the disquieting notion that throughout the hundreds of billions of light years that encompass the known universe, this small, blue planet could be the only island of life. And in all that space, there's only one of you.
Kinda makes you feel special, doesn't it?