Charleston Observatory

The Scale of the Universe

2003-2015 CL Astronomical

The scale of the Universe is simply astounding. The best way for the layperson to understand the distances we are dealing with is not to use words like Parsecs or light years, but rather to use easy to understand analogies.

Analogy #1 - The Earth-Sun Distance

Suppose that our Earth is the ball in the tip of a ball-point pen. How big would the Sun be, and how far away from the pen tip? First, Hold the ball-point pen up in the air. Now hold a ping-pong ball about 15 feet away from the pen tip.

The ping-pong ball represents the sun, and the ball in the tip of the pen represents the earth. This is approximately a size and distance scale model of the Sun and Earth. The moon would be the size of a dust speck beside the ball in the pen. When we observe sun-spots on the sun, these magnetic storms are often larger than the earth itself. Amazing...

moving beyond our sun...

Our sun is a star. The closest star system to our Sun is Proxima Centauri, in the Alpha Centauri complex. If Proxima Centauri were a second ping-pong ball, how far away must we place it from the first, to stay within our scale model?

The answer is, start driving. And be sure to bring some food for the trip, as you must drive some 2300Km away to place the second ping -pong ball in it's correct location to represent Proxima Centauri, while the first ball represents our sun.

That's about the distance from Toronto to Tampa Florida!! This helps us understand why we cannot resolve individual stars into discs from any earth-based telescope, including Hubble. The only reason that we can see them at all is due to the copious amounts of light they emit. Our own sun is no exception, when you consider the light from a full or partial moon, is simply the moon reflecting a very small portion of sunlight back to earth.

other bodies in our solar system...

Continuing with our model, Saturn, within our Solar System, would be about the size of a pea, and would be about 150 feet away from the ping-pong ball representing our Sun, while Jupiter would be about the size of a small marble about 100 feet away from the ping-pong ball.

moving out of our solar system and into our galaxy...

When you look up into the night sky, you can see millions of stars. All the stars you are looking at are within our own Milky Way galaxy, an island of stars and matter in a vast and strange universe. Our Sun and Proxima Centauri are but two of the millions of stars within our own galaxy, The Milky Way. We can see the Milky Way edge on, stretched out across our sky. It is most prominent in the summer in North America, as we are viewing the thickest portion of it. The light that makes the Milky Way glow as a whitish haze is actually the combined light from billions of stars, all further away than Proxima Centauri. Try looking at the Milky Way with a pair of binoculars some night, you'll be amazed at how many stars there are.

Analogy #2 - Milky Way Galaxy - How big is it?

Our Milky Way galaxy is simply huge. To fully comprehend just how large, again we turn to an analogy. Just how big is our galaxy? Let's now pretend that our galaxy is a kid's sandbox, and our sun is a grain of sand in a sandbox. The Earth is a miniscule dust speck near the grain of sand, too small to be seen without a microscope.

If our sun were a grain of sand in this sandbox representing the Milky Way galaxy, the sandbox would be somewhat oval and yet flat, and would be about 20 feet in diameter. The sand would be about 12 inches thick in the center, and thinner towards the edges.

moving out of our own galaxy ...

Now that we have an idea of how large our own galaxy is, we can turn our sights to more distant objects. There are billions of other galaxies in the Universe besides our own. The closest large galaxy to our Milky Way galaxy is the Andromeda Galaxy, just barely visible naked eye from a dark sky site. The space between galaxies is very empty, devoid of stars and even dust. About the only tangible thing that exists between galaxies is light itself.

Now how far away is the Andromeda Galaxy?

Analogy #3 - Milky Way - Andromeda Galaxy Distance

Continuing with our analogy where our Milky Way galaxy is the 20 foot sandbox, we can determine how far away the next closest sandbox be to ours, if that sandbox were to represent the Andromeda Galaxy (or M31).

As in Analogy #1, quite a distance away. The next closest sandbox representing Andromeda would be approximately 2000 ft away, about 1/3 mile away. This sandbox would be quite similar in appearance to our own, perhaps slightly larger. Some piles of sand lay scattered nearby this sandbox, disorderly "mini" galaxies, seen below as M110 (below M31) and M32 (above M31)

Note that the comparative distance between the Milky Way galaxy and Andromeda galaxy is smaller than the comparative distance between the stars within our galaxy. This is exactly the case in reality as well. The galaxies are clumped into groups, and M31 happens to be within our Local Group of galaxies.

moving out of our local group of galaxies...

Analogy #4 - Our Local Group to other Galaxy Groups distances

For this analogy, our Milky Way galaxy will again remain the 20 foot sandbox.

Our Milky Way galaxy and Andromeda are members of the "Local Group" of galaxies, which includes other member such as M33 (Triangulum) as well as the Large and Small Magellanic clouds. The large and small magellanic clouds are akin to disorderly piles of sand that are on the grass about 5 feet from our sandbox, the Milky Way, while Andromeda is another sandbox about 1/3 mile away.

The next groups of galaxies are the M81 group, the Maffei group, the Sculptor Group (including the magnificent NGC253), and the M83 group.

Each of these groups would be like other groupings of sandboxes from about 2 miles to away, perhaps some other schoolyard..

The galactic groupings have been studied extensively, and have been found to be structured into strings and clusters. The Virgo Cluster contains our local group and other nearby galaxy groups, much like cities each with sandboxes may be structured along a river for example.

moving out into the remainder of our Universe...

Analogy #5 - The rest of the Universe

For this analogy, our Milky Way galaxy will again remain the 20 foot sandbox.

The groups of galaxies we looked at in Analogy #4. represented several schoolyards, each with several sandboxes. Now let's see what's left in our observable universe...

The rest of the universe can be represented by our entire earth, with all the continents having thousands upon thousands of "sandboxes", each representing a galaxy. The Earth would have to be filled with sandboxes as well, such that when we sight a line through the earth, multiple galaxies would lie upon our sight line, with some being closer than others.

This is in effect what the Hubble Deep Field revealed, millions of galaxies. The deeper we look, the more galaxies we can see.

In conclusion; by means of analogy, we can see that our earth is but a speck of dust on the side of a grain of sand, in a sandbox that is about 20 feet diameter, with the closest sandbox being about 1/3 mile away, and our local group of galaxies would be but a collection of sandboxes in a space about the size of a small city, and that there are other cities with groups of sandboxes as well, expanding out to the whole earth, with billions of other sandboxes each representing other galaxies, each containing billions of stars.

To be frank, I find it humbling. I also find it amazing that us people, living on that little fleck of dust, can set up a telescope in our backyard and witness this grand scale universe in action, by simply magnifying the view. We also have been given the ability to attempt to comprehend the scale of it all.

Let it be said that it truly is an incredible Universe in which we live.

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2003-2015 CL Astronomical