Oolon Colluphid

Space, as Douglas Adams noted, is big. Really big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the street to the chemist, but that’s just peanuts to space.

Whilst knowing this intellectually, it was brought home to me this evening rather forcefully, so I thought I’d share.

Apollo 13 was on the telly. My not-quite-five-year-old daughter was watching some of it with me. Naturally a lot of questions arose. But she was intrigued by it taking four days to get to the Moon.

So, I got our globe down off the top of the cupboard, and the encyclopedia out. Okay... the globe is 26cm (10 inches) in diameter, and a quick bit of calculation meant that the moon was therefore about the size of a satsuma, on that scale.

So, how far away should I place it, to show the distance? I strongly recommend you try this at home. Get a couple of balls, and measure the diameter of the large one.

The Earth’s equatorial diameter is 12,756km. And the Moon orbits us at an average distance of 384,400km. Divide the latter by the former, and you get how many Earth diameters away the Moon is: how many larger-ball diameters away the satsuma or small ball needs to be. Well, the answer is just over 30.

Doesn’t sound much? If your ball, as my globe is, is just 10 inches in diameter, your little piece of fruit, smaller than a tennis ball, has to be 300 inches away. Still not sound much? It’s twenty-five feet away.

If that doesn’t shock the shit out of you, you are either an astronomer or haven’t tried it out on the floor of your living room. This is only the Moon we’re talking about. Our nearest space neighbour.

The Sun, by contrast, is about 93 million miles, or 150,000,000km, away. On the scale of my ten-inch globe, the Sun is 117,647 inches away. 9,800 feet. 3,268 yards. Well there’s 1760 yards in a mile, so on the scale of a ten-inch globe, the Sun’s 1.8 miles away.

If that doesn’t blow your mind, I’ve either screwed up royally in basic maths, or... I dunno. It’s blown mine.

Cheers, Oolon

sakrilege

My mate has put the planets in our yard to scale with the sun being a 12in softball which is 3.75 in diameter.

Mercury 13' away
Venus 24'
Earth 33', Moon 1' away
Mars 51'
Jupiter 174'
Saturn 319'
Uranus 641' (not quite in the yard anymore & there is 4 acres)
Neptune 1003'
Pluto 1317'

Coragyps

I've done a demonstration for schoolkids for years now along the lines of this. I use a beachball - 14 inches or 35 cm diameter - for the Sun. This puts Earth 125 feet = 37 meters away, and represented by a 1/8 inch (3 mm) ball bearing. Jupiter is a golf ball 625 feet (190 m) from the Sun, and Neptune a marble (.5 inch/12 mm) about a kilometer away.
Now, to get the idea of BIG, talk about the closest star: 12,000 miles away. Don't even calculate how far the scale distance is to the Andromeda Galaxy......

Edit:
Sac, I just saw your post. I desperately would like to get a school project started with kids here in town, with the Sun modelled by the globe-ish water tower, maybe 40 feet diameter. Pluto would be in the next town north, some 40 miles away.

Quantum Ninja

I found a cool little page here:

http://www.exploratorium.edu/ronh/solar_system/

You don't even have to do the math yourself anymore!

Guerrilla

I remember Bill Nye doing something similar to the above. He had scale model planets set up along side the road, and he would bike between planets. I think he traveled several miles before reaching pluto, and earth was only about the size of a tennis ball. If you can get your hands on that episode, I'm sure your daughter would find it very interesting.

Lobstrosity

I think I remember that Bill Nye thing. An analagously interesting demonstration is carrying out the same process for an atom, using perhaps a golf ball to represent the nucleus and a football field to represent the entire atom. It's interesting to note that nearly all of the mass of an atom is in its nucleus, which occupies a volume roughly on the order of a cubic fermi or so (10^-45 to 10^-42 m³). Atoms themselves, however, generally have a volume roughly on the order of a cubic Angstrom (10^-30 m³). That's a lot of empty space in there between the electrons and the nucleus, relatively speaking (a difference four or five orders of magnitude when dealing with radius)!

Coragyps

And to continue flogging this topic, the ball-bearing Earth in my scale model has scale-model humans on it - adults about two hydrogen atoms tall.

goat37

Is the universe truly infinite? Would it matter if it were, or were not?

I was thinking about this, and maybe I could get a good answer. If you need to post in 'math' that's fine, I will understand it.

Here goes:

Even if the universe were not infinite, you could still never get to the 'end of the universe'. I know there are theories out there that the universe is like living on the outside of the globe, and you would just end up at the point you started but...

In order to get moving 'fast' enough to get to the end of the universe, you'd have to travel faster than the speed of light. But at this point (from what I understand) you would end up moving back in time, not forward in space. So before you got to the 'end' of the universe, you would get back to the beginning or the big bang.

Could this be correct?

eh

No, it has nothing to do with the speed of light. Take the image of a curved surface for the globe, and notice how we will never fall off, no matter how far east, west, north or south we go. Then apply that to the universe to get a curved volume. Though we can't imagine what it looks like, we can see how movement along any of the x,y,z axis will never allow us to reach an edge, much as how we can never reach an edge of the earth on the x,y axis.

For all we're concerned, space might as well be infinite.

JP2

Wow, take a look at one of the links on the site that Quantum Ninja provided:

http://www.umpi.maine.edu/info/nmms/solar/index.htm

If the Sun were 49.5' across, the Earth would be 5.5" in diameter and sit 1 mile away. Pluto would be the size of a marble, lying 40 miles away (which explains why it took so long to find - imagine pinpointing a marble, submurged in darkness, from 40 miles away). Doing some quick calculations, Proxima Centauri (the closest star) would - on the same scale - would therefore measure some 7 feet across and lie some 4,000 miles away.

Mind-boggling.