How Far is Far?
We generally measure our world in terms of inches or centimeters, miles
or kilometers. Some of us are better at judging distances and sizes than
others, but usually we are not too far off. A thousand miles or kilometers
may be harder to grasp, but it can be done if we think in terms
of "several days drive" or "several hours flying." But what about space? The universe is an incredibly vast place. What does "distance to the moon" really mean. How far is the Sun? What about the nearest stars and galaxies?
Astronomers soon came to realize that measuring the universe in terms of
miles or kilometers was very impractical. They began using light years.
You may remember that light is the fastest thing in the universe, traveling
at an astounding 186,000 miles per second. Our Sun is about 93
million miles away, and it takes light 8 minutes to reach us. 8 light minutes is easier to think of than 93 million miles. Distances to stars is measured in light years, distances to galaxies are measured in millions of light years! And what of size, how big is Jupiter? How big is a star?
Fortunately there is an easier, and far more amusing way to grasp the vastness of the universe.
In a fanciful
imaginative trip, suppose you could get in your car and drive to the Sun.
How long would it take you? Lets set the speed limit at 65 miles per hour,
and lets give ourselves a never-ending fuel supply. Driving nonstop, it
would take us 163 years to travel the 93 million
miles! I have two friends who, considering their driving habits, could take some years off that number, but it is still longer than a human lifetime. What if we could fly? How about a jet airliner that travels at about 500 miles per hour? Try 21 years! At least that is in one lifetime.
A good analogy to demonstrate the Sun's size and the distance to the planets
is if the Sun were the size of a large navel orange (about 5 inches in
diameter) how big and far would the Earth be? On this scale, the Earth
would be the size of a sesame seed about 49 feet away. Pluto, the
most distant planet, would be the size of a grain of sand, 3400 feet away! The nearest star to the Sun, Proxima Centauri, would be about 2500 miles away.
Jupiter is the largest planet in the solar system. It contains 71 percent of all the mass of all the planets put together. But just how big is that? If the Earth were represented by a dime, Jupiter would be the size of a dinner plate! Jupiter's great red spot, the large storm that has been raging for over 300 years, could swallow up 3 Earths!
And how about the distance to the nearest star? A car trip to one of them
would make that trip to the Sun look like a cruise to the local mini mart.
If we decided to drive to Proxima Centauri, at 55 miles per hour, it would
take a whopping 52 million years. An Apollo spacecraft,
which made the round trip to the moon in 6 days, would take 850,000 years to reach the nearest star. If we decide to go star hopping, clearly, we need something much faster!
And what of our galaxy, the Milky Way, what is our solar system's place in this gigantic myriad of stars? If the sun and all the planets could fit into a coffee cup, the Milky Way galaxy would still be the size of North America. We are truly a speck in the cosmic sea!
Copyright © 2001 Kathy A. Miles and Charles F. Peters II