Illinoyancing with the Stars

When Mom came to town a couple weeks ago, we went on a little tour of campus. On that tour we saw the University of Illinois Astronomical Observatory. I had a vague notion that it had some historical value, but I didn't realize how much until later.

Architect and U of I Professor Charles A. Gunn designed this Observatory built in 1896. He built it in the Colonial Revival style, a somewhat fuzzy term, but I'll explain that in a later post. It served as a location for astronomical research into the late 1950s. Since then the University only uses it for instruction and random events open to the public. The Observatory entered the National Historic Registry in 1989.

The first director of the Observatory, Joel Stebbins, pioneered the science of photoelectric photometry. Yes, I'll explain what that means. Before Stebbins, astronomers measured stars by their apparent magnitude, a fancy name for how bright it looks when you crane your head back at night and look up at the sky. This gave scientists very inaccurate information about stars: the Earth's atmosphere filters a lot of light and it takes no account of distance. One star may be bigger and brighter than another, but if it's farther away than the other star, it looks smaller and dimmer.

In the early 1900s, Stebbins, instead of using his eyes, started recording information with a photoelectric cell. You've seen photoelectric cells on calculators and the roofs of houses. They are the source of solar energy. They absorb light and convert it to electricity. Basically, he directed light coming through the telescope into a photoelectric cell to perform photometry, the measure of electromagnetic radiation.

What is electromagnetic radiation?

Good question. Imagine you're sitting in your bathtub, watching your rubber ducky floating in front of you. If you pat the water, you create these little ripples that make the rubber ducky bob up and down. What happened? You created energy that moved through the water in the form of waves. If you pat the water lightly, you create small waves and if you pat the water vigorously, you create large waves. The size of the waves affect the behavior of the rubber ducky. Small waves make it bob slightly; large waves make it rock like a boat.

That was simple. You can see both the waves and the effects. What about waves you can't see? Clap your hands. You just created waves of energy that move through the air instead of the water. Instead of making a rubber ducky bob up and down, these waves enter your ears as sounds. If you clap lightly, you create small, soft waves. If you clap vigorously, you create large, loud waves.

Here's where it gets crazy. Imagine you're a big yellow ball of fire. We'll call you the Sun. Deep in your belly, you're squishing Hydrogen atoms together to make Helium atoms in an act called Nuclear Fission. Nuclear Fission releases energy in the form of waves that move, not through water or air, but through the electromagnetic field. Just like the size of the waves in the water have different effects on the rubber ducky, the size of the waves coming out of you, the Sun (or any star, for that matter), has very different effects on pretty much everything.

We call very tiny electromagnetic (EM) waves X-rays. These very tiny waves can pass through soft tissue, but not dense bone, so doctors use them to take pictures of fractures. If the waves get a little bigger, they become UV rays, that don't pass through tissue. Instead, your skin absorbs them and burns. When the waves get a little bigger they become visible light. These waves bounce off of just about everything, but they are absorbed by the rods and cones in your eyes.

Going up the scale, we have infrared waves, also known as heat. There's a thin line between infrared waves and visible light, which is why on a summer day, you can see the waves rising from the hot concrete. Also interesting: UV waves are small enough to pass through the windshield of your car. Your car seat absorbs them, then releases them again as infrared waves, which are too large to escape through the glass. This heats up your car in the summer in a process called the Greenhouse Effect.

If you increase the size of the waves again, you have microwaves, which we use to cook popcorn and TV dinners. After microwaves, the huges splashes in the EM field get very exciting. They become radio waves, which we use to watch TV, listen to music, talk on cell phones, and find our ways with Garmins.

Here's a chart that shows the EM Spectrum, all the different wavelengths side by side:

NASA

All of those different types of waves come out of stars. Once Stebbins found a way to accurately measure the EM radiation from stars, scientists gained the ability to determine many characteristics about stars: how big they are, how far away they are, what they're made of, and how bright they are. Instead of apparent magnitude, astronomers could measure absolute magnitude, the actual brightness of a star. Stebbins' practice yielded such precise information, it became the standard practice for all astronomers. Using this technique, scientists were able to position stars on the Hertzsprung-Russell Diagram. You will find an H-R diagram in any Astronomy book. It's like the Periodic Table for astronomers. It lays out all the known stars in the universe by brightness and color.

http://www.eso.org/public/images/

And we know all this about the universe because of work done at the University of Illinois.

Parting Shot
This is just for fun. Everything in space emits some sort of EM radiation. Even planets release radio waves that scientists can record and play back. The video below features a recording of radio waves from the planet Saturn. They've modified the signal a bit to render it audible to human ears, but this is the actual recording they released. The sounds of Saturn: