solar system

All posts tagged solar system

Credit SiBr4 – CC-BY-SA

We live on a rocky ball about 12,750 kilometers through and 40,050 kilometers around its widest diameter. It has a mass of about six quadrillion megatonnes, which is so ridiculously large compared to things we’re used to that it doesn’t really mean anything to us. Our size compared to Earth’s size is roughly equivalent to the size of viruses compared to us.

That is not to imply that humans are like germs living on Earth. It just provides some perspective on where we are. To go a little further, the next level at the same ratio compares the size of the planet Earth to the size of the whole Solar System. Give or take a few billion kilometers. It’s not an analogy that can stretch forever. (Here’s a link to a video that goes from the very small to the very large – 10 minutes)

And it doesn’t imply that humans are merely an unimportant example of a repeating theme. After all, why is our size one of the levels? We could just as easily be included with all of life to fall between the very small and the very large. As in – subatomic particles – living things – planets and stars. But that’s another analogy that shouldn’t be pushed too hard.

We choose humans as a level because we’re human. We tend to look at things relative to what we’re used to, so we don’t think twice about our size being one of the steps on the ladder. Besides, it was necessary to use something familiar as a point of reference in such a wide array of dimensions.

The dimensions of the physical universe are measured by such huge numbers, both hugely big and hugely small, that they don’t convey much meaning on their own. The very large is measured in billions of light years. Light years are trillions of kilometers each. Even a single kilometer is big compared to us. The small is measured in fractions of meters, changing the numbers from positive to negative right about our size. The very smallest things are such small decimals of a meter that we don’t write them out in full, using special mathematical shorthand instead.

In all that vastness, all that range of realities and possibilities, what is most amazing is that part of it is conscious. A narrow band in the middle has produced something that can look out and try to understand the whole thing.

I think we can justify being a little self-centered.

Photo credit - NOAO

Photo credit – NOAO

The American National Optical Astronomy Observatory has provided a model that can be used to visualize the size of the Solar System. Various objects are used to represent the Sun and planets, such as a ball for the Sun and a peppercorn for Earth. Units will be in inches and yards, since the source is American, with metric equivalents in brackets. For example, the Sun is represented by an eight inch(20 cm) ball, and the peppercorn representing Earth is .08 inches(.20 cm) in diameter.

Three of the planets, Mercury (shown above in transit of the Sun), Mars and Pluto, are pinheads. Mercury’s pinhead is .03 inches(.08 cm) across. Mars is .04 inches(.10 cm) and Pluto is .01 inches(.03 cm.) We’re including Pluto as a planet even though it has recently been reclassified as a Kuiper Belt Object. Two planets, Venus and Earth, are peppercorns at .08 inches(.20 cm) across. Jupiter is a chestnut at .90 inches(2.40 cm.) Saturn is a hazelnut of .75 inches(2.00 cm) diameter. Both Uranus and Neptune are peanuts of .30 inches(.80 cm.)

Now we have one ball, one chestnut, one hazelnut, two peanuts, two peppercorns and three pinheads. Next we need a place to lay them out to show how far apart they are. We can’t do it indoors because there simply wouldn’t be enough room, so we have to go out. The back yard is too small, too. None of the playing fields is big enough, either. The airport just might do it. We’ll put the Sun, the twenty centimeter ball, down at one end of the airport, in the grass near the fence because the paved runway isn’t long enough by itself. Then we’ll pace off the distances to the planets, assuming one yard (a little less than one meter) per pace.

The first planet out from the Sun is Mercury, at ten paces. We’ll put the first pinhead there, and we’d better mark it with a flag so it doesn’t get lost in all that space. Take another nine paces and put down a peppercorn for Venus. Another seven paces and we can mark Earth with the second peppercorn. Then there’s a jump of fourteen paces to get to Mars and its pinhead. We’re forty paces out now and we’ve placed the four inner planets already.

Now we start to cover ground. Jupiter, the largest planet in the Solar System, bigger than the rest combined and almost one tenth of one percent as massive as the Sun, is 95 paces beyond Mars. Put down the chestnut. Saturn the hazelnut is next at 112 more paces. Uranus is another 249 paces and Neptune 281 paces beyond that. Down go the peanuts. All we have left is one pinhead for Pluto, which is another 242 paces. At a total of 1,019 paces, we might still be inside the fence at the far end of the airport. If the Sun wasn’t shining at the other end, we’d never see it.

To put it in perspective, the Moon, which is the farthest any human has gone, is 2.4 inches(6 cm) away from Earth’s peppercorn. Mars, one of the closer planets, is over 200 times as far as that. This model shows how big and empty space really is.

Here’s a bonus photo from NOAO, showing, from top to bottom, the Moon, Venus, the star Spica and Jupiter, in conjunction above an observatory in Chile.

Photo credit - NOAO

Photo credit – NOAO