Spectroscopy and the Chemical Characteristics of Stars

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  • 0:02 Light & Characteristics
  • 0:42 Spectral Lines & Spectroscopy
  • 2:06 Atoms, Electrons,…
  • 5:45 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will explain how astronomers find out the chemical composition of a distant star using spectral lines and spectroscopy, and how this relates to atoms, electrons, and photons.

Light and Characteristics

When you look at the sun, a lamp, or a neon sign, what you see is light being emitted by that object. But I'm going to shed some light on something here. Light can give us a lot of clues as to the characteristics of something. Maybe you've already watched the lesson where I describe how light can clue us in to how hot an object, like a distant star, actually is.

But light can tell us even more than the temperature of something. It can actually reveal a distant star's chemical make-up or the reason why fireworks are a certain color! Who knew that something as simple as the light being emitted by your computer screen right now, can tell us all of this information? I think that's pretty neat.

Spectral Lines and Spectroscopy

And good thing, too. I mean, we don't have the means to travel to distant stars, and even if we did, they would be so hot that we may not even be able to get close to them. Anyways, that's where light comes into play in helping us reveal the characteristics of distant stars, or even that of our own, the sun!

Scientists have known for quite some time that when you burn a chemical, it will light up. The burning of chemicals during experiments may help reveal why scientists are, you know, a bit out there sometimes - those fumes. Anyways, if you pass the light of a burning chemical through a prism, a specific color spectrum will form. A spectrum is an arrangement of electromagnetic radiation (which includes visible light) placed in order of wavelength.

The color spectrum of these chemicals will reveal patterns of thin, bright, or dark lines, called spectral lines. It's like a barcode linked to a specific item, but in color. In our case, it's linked to a chemical substance as opposed to something like a phone, box of cereal, or another thing at the store. The use of unique patterns of spectral lines to identify a chemical substance is known as spectroscopy. These spectral lines and spectroscopy are very important in helping astronomers understand the chemical make-up of a distant star.

Atoms, Electrons, Orbits, and Light

To truly understand how this occurs we need to, unfortunately, get into some nitty gritty details, which I've tried to simplify for you as best as possible. Chemical substances are made up of atoms. An atom, as you probably already know, is made up of protons, neutrons, and electrons. The electrons are found at the outer edges of the atom, the electron orbits (or a.k.a. energy levels). The behavior of electrons in these outer edges of an atom is what actually generates light. Although electrons do not truly move precisely in a circular orbit as that shown on screen below, such a model is best used for an easier understanding of how this happens.

Representation of an electron orbit
representation of an electron orbit

The smallest and most tightly bound orbit, nearest the atom's nucleus, is the one with the lowest energy level (a.k.a. an atom's ground state). If an electron wants to move up in life, it will have to move up to a higher energy level. But the only way to do this is to give the electron some energy, a jolt, to get it moving up a level. Otherwise, electrons would prefer to stay at the lower energy levels instead.

In real life, if you want to move up in life, you have to work hard and you can't work hard without absorbing energy from food to give yourself an energy rush. If you want our cute little electron to move up in life, to a higher orbit, we have to supply it with a jolt of energy as well. Electrons don't care much for absorbing food for energy. Instead, one of the ways they can move up an energy level is by absorbing a photon, a packet of electromagnetic waves with a specific energy.

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