Sunday, August 21, 2011

The Age of the Universe: Part 2

Now that we have the local universe mapped pretty well, we can notice some things about the stars themselves. Once again, we use simple devices for measuring and cataloging stars.

One thing we can notice is that stars are different colors ranging from red to yellow to white to blue white. Now suppose we look at two white stars and measure that their color is almost exactly identical. We then figure the distance to these stars. One is twice as far away from Earth as the other. As we see it them from Earth, the more distant is one fourth as bright as the other. This fits in perfectly with the inverse square law of light.

What is the inverse square law of light? Simple, if you have a light source of known brightness (a candle for example) and move it away from the observer, it will dim in a predictable manner that is the inverse of the square of the distance. If a candle is one foot away from you and you move it two feet away from you, it will be one fourth as bright. Move it three feet away from you and it will be one ninth as bright... and so on. For an illustration and in-depth explanation of the inverse square law, click here.

Now by the same token, if you have two sources of light at different distances and they seem to be equally as bright to you the observer, they would have different brightnesses if they were the same distance from you. One candle one foot from you will give the same illumination as four candles two feet from you.

Fortunately, for those of us who want to measure the distances to the stars, we can see the the same law of physics applies to the stars as it does to candles. And the inverse square law of light is a pretty good thing, too. If the star Sirius (which was mentioned in the previous article) were as close as the sun, it would seem more than 23 times brighter.

Knowing that stars of the same kind have an intrinsic brightness gives us a yardstick for measuring the size of our home galaxy, the Milky Way. We could now measure our local universe to distances on the order of 100,000 light years. If we see something 100,000 light years away, we are seeing it as it was 100,000 years ago. This is two orders of magnitude older than the age of the universe as given by creationists. The calculations put forth by James Ussher in 1647 start to become questionable.

We haven't even left our galaxy yet and we can see that the universe is older than creationists would have us believe. We've barely started the journey.

We'll look at other galaxies along with the size and age of the entire universe in part 3.


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