The Building Blocks of the Universe


“The Building Blocks of the Universe.” When you put it that way, atoms sound less like a topic specifically for a chemistry class and more like something astronomers might discuss.

They really are. I’ve got a fantastic reason to include atoms under astronomy, and its name is stellar spectra.

We’ve encountered stellar spectra before in these astronomy posts. When I wrote about the spectrograph, an instrument astronomers use to study data, I talked about spectral lines. I also promised we’d come back to elaborate on that later.

We’re not actually going to talk about the spectrograph in this post. I’m saving that for another time. For now, I’m going to cover atoms in a little more detail.

That way, we’ll have a better understanding of how they interact with light later on—and that will help us understand the spectrograph.

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Tycho Brahe, the Observer


It is surprisingly difficult to find a flattering image of Tycho Brahe.

Honestly. Do me a favor and do a Google image search for the guy. It’ll come up with all sorts of disfigured images, mostly because his nose got messed up in a sword fight…

I know what you’re thinking. A classical astronomer in a sword fight? Suddenly these people seem less like heroes of modern-day science and more like human beings with lives of their own.

Tycho certainly fits the trend. He’s known for being quite the unpopular sort. Bad-tempered and vain, there were few who respected him for more than just his astronomical accomplishments—and even those were few.

So why is he even important, then?

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The Ptolemaic Universe

Ptolemy Retrograde Motion.jpg

Claudius Ptolemy lived about five centuries after the Greek philosopher Aristotle’s time. Aristotle’s model for the universe—the first geocentric model, with Earth at the center—was still widely accepted, and Ptolemy sought to improve it.

Ptolemy was one of the first of the ancient Greeks to be a true astronomer and mathematician, rather than a philosopher.

Where Aristotle, Plato, Thales, and Pythagoras before him had tried to use “pure thought” to understand the nature of the heavens, Ptolemy set about to perfect the geocentric model mathematically.

This was a huge step forward for science as a whole, as science today relies heavily on mathematics.

In Ptolemy’s time, science didn’t really exist yet. The Greeks preferred to just think through problems logically and reasonably, and if the logic they used was based on untrue assumptions…well, no one was the wiser.

But Ptolemy came up with the wonderful idea to line up observations of the sky with mathematics. And even though Aristotle’s view of the universe shackled him, he moved science forward with great strides.

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The Celestial Sphere

When you look up at the night sky on a clear, dark night, it seems as if the stars are glittering like bright thumbtacks on a great canvas above you. (You can get a similar effect–with less light pollution–from a planetarium like the one above!)

In reality, space is not like a canvas, and stars are not like thumbtacks. It would be more accurate to describe us Earthlings as floating in a vast, cosmic ocean.

Astronomers know this. But still, it’s helpful to map the sky in exactly the way it appears to us: as a sphere around the Earth. And so we use a model called the celestial sphere.

Telescopes operate solely based on the celestial sphere: the mechanism that aims the telescope doesn’t need to know anything about how far away an object actually is in the cosmic sea, just where it is in the sky.

That makes the celestial sphere a useful reference tool. Researchers need to communicate with telescope operators and say, “Let’s look over there now.”

And so, everything is mapped on a spherical model that pretends the night sky is a finite globe, inside which the Earth hovers like a bubble.

So…what exactly is the celestial sphere?

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