Scales
This is a 16 meter by 16 meter scene. A meter is close in size to a yard, for those of you who still think in English units. And you see someone sitting on a bench.
Next we zoom out and see a scene that is 1 mile square, and you start seeing a city. At 100 miles on a side, you see a landscape. It seems pretty big. You probably wouldn’t want to walk it.
We can back up still further and see the diameter of Earth, 12, 756 km across. Which is big, until you compare it to the distance between the Earth and the moon, 384,000 km. However, it is 150,000,000 km from the Earth to the Sun. If you could take a jumbo jet from the Earth to the Sun, it would take you 17 years to get there! It’s pretty far away!
Now we don’t like having numbers that big. Too many zeros. So, we are going to just change units. We are going to switch from kilometers to astronomical units. Copernicus came up with the Astronomical Unit (AU). He wasn’t sure how far the Sun was from Earth, so he just defined an AU as the average distance between the Earth and the Sun. So, the distance between the Earth and Sun is just 1 AU.
Backing up, at 100 AU across we see the Solar System. This is 100 times the distance between the Earth and Sun! You can see why it takes so long for us to get a spacecraft into the outer solar system.
At 10,000 AU you see the almost empty solar neighborhood. Not even the next closest star to the Sun is that close to us.
So, we back up again to 17 light years across. A light year is a measure of distance, not time. It is the distance light travels in a year. Since light travels very quickly, it goes a long way in one year. In fact, it travels 63,000 AU (10,000,000,000,000 km) in one year. The next closest star to the Sun is Proxima Centauri (visible from the southern hemisphere) at approximately 4.2 light years away.
An interesting thought for you… If Proxima Centauri is 4.2 light years away, how long did it take the light we see from it to get here? (ANS: 4.2 years.) So, are we seeing Proxima Centauri the way it looks right now? (ANS: No! We are seeing what it looked like 4.2 years ago when the light left the star. ) What if you were looking at a star 100 light years away? Would you be seeing it the way it looks now? (ANS: No! You’d be seeing it the way it looked 100 years ago, when the light left the star. The star could’ve blown up since then and you wouldn’t know it.) Looking out in astronomy is like looking into a big time machine. The further out we look, the farther back in time we are looking.
The Sun is only 8 light minutes from us, so we are seeing the Sun as it looked 8 minutes ago. (But don’t look at the Sun! It will hurt your eyes!)
Moving outward still, at 1700 light years across, we see the extended solar neighborhood. You can see our nearest stellar neighbors!
Moving outward, we would be able to see the Milky Way galaxy. Since we are inside the Milky Way, we can’t take a picture from the outside, but our galaxy is a grand design spiral somewhat like the whirlpool galaxy. It measures between 75,000 and 150,000 light years across and only about 2,000 light years thick. That means, if we could see all the way across the disk of the galaxy, we would be seeing stars as they looked about 150,000 years ago! For those of you interested in communicating with aliens on the other side of the galaxy, even if we sent a message at the speed of light to them, it would take up to 150,000 years to get there. If they were on the ball and responded promptly, it would take another 150,000 years to get back. So, 300,000 years after we sent the message we’d get a response. You can see why the distances are daunting in this situation!
Galaxies are grouped in galactic clusters. Our cluster is called The Local Group. At several million light years across, we start to see our group.
Galactic clusters are also found in groups called superclusters. Our supercluster is the Virgo supercluster (not to be confused with Virgo the constellation or Virgo the cluster). Even at the greatest scales, we see structure. Some see a bubble-like structure in the supercluster arrangements.
So, we have looked at huge scales, but what about small scales? Dropping back to our 16 meter campus scene, we then zoom in to a 1 meter scene… of a person sleeping instead of studying.
Zooming in further we see a hand, and then skin, and then very magnified skin. Zooming in further, we find capillaries, lymphocytes, and even coils of DNA! At a nanometer across, we get a clear view of the genetic message in DNA.
Scales are not just for size, but a useful for time, too. If you were to scale the entire history of the universe (all approximately 13.7 billion years of it) down in to 1 year, with the Big Bang at the first moment of January 1, then Earth wasn’t formed until mid-September. The mammals appeared on December 26, and all of human prehistory and history take place in the last half hour of New Year’s Eve. The universe was around a long time before Earth was formed and even longer before humans got here. We are so very young and new in the universe!
So are you feeling small and young?