Friday, August 19, 2011

The Age of the Universe: Part 1

I wrote a bit about the Traveling Creation Museum and its interesting (if not entirely convincing) curator, Sean Meek. I decided that I'd cool off a bit before saying too much and a couple years should be long enough.

Mr. Meek was talking about what astronomers know about the beginnings of the universe and he said that they simply "make things up." With that kind of statement, you might see why I wanted to calm down a bit before commenting further. He said other nonsensical things but this was the one that really got under my collar. He also belittled findings based on radioactive decay dating (potassium-argon decay for one). He tried to dismiss all of science under the blanket idea that because we weren't there, we can't know.

And it's true that there are no living witnesses who can attest to the existence of anything that happened more than 6000 years ago. I'll grant him that. But there is ample evidence that one needs only a brain, some simple math and a few simple scientific instruments that demonstrate that the universe in which we live is several orders of magnitude older than Mr. Meek would have you believe.

First, we figure out the distance to the moon. You can't tell by just looking at it and ancient people might have thought that if you stood on a high enough mountain, you could touch it (legends speak of such things). But determining the distance to the moon is actually pretty elementary. Set up a simple observatory. Set up a similar facility a known distance away (preferably a few hundred miles). Have your astronomers measure the angle between the moon and a nearby star. This gives you the parallax of the moon. Simple trigonometry and you have the distance to the moon, about 240,000 miles.

Second, now that we know how far away the moon is, we measure the distance to the sun. We know it's farther than the moon because it passes behind the moon during solar eclipses. We use the same sort of method we used to determine the distance to the moon. This time, it helps if we have accurate clocks to measure the angles because we can't use the stars (they're not out in the day time). But again, it's a matter of simple trigonometry to determine that the sun is about 93 million miles away.

Now with the work of Johannes Kepler and Isaac Newton, we can figure the orbits and the distances to the planets. We have the scale of the solar system which is about 8 billion miles from side to side (using the orbit of Pluto as sort of an edge... if we use the heliopause, it's bigger still).

Now we only need one observatory to go to our next level of measurement: the distance to the stars. We seek out a nearby star that can be seen in two different seasons, preferably opposite seasons (spring/autumn or summer/winter). Sirius is a good candidate. We measure its position against the background stars when it first starts appearing in the morning skies in August. Then we take a similar measurement the following February. We know that if we take these measurements 6 months apart, the two positions of the Earth will make a straight line with the sun in the middle. That line segment is about 186 million miles. Again, simple trigonometry and we find that Sirius is about 54 trillion miles away. It takes light a bit under 9 years to travel that distance so we say that Sirius is a little under 9 light years away (8.6 give or take 0.04 light years if you want to nitpick). We repeat this procedure for all the stars that are close enough for us to measure this way. That's about 100 light years which is right in our own backyard, celestially speaking. And that's a pretty huge number of stars when we see that there are about 50 stars within 17 light years of our sun.

Part 2 will discuss how we determine the distances to stars that we can't measure in this manner.


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