Back To CourseBasics of Astronomy
28 chapters | 325 lessons
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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.
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.
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.
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.
Only a certain photon, one with exactly the right amount of energy, can move a unique atom's electron from one energy level to a higher one. Otherwise, the atom will not be able to absorb a photon if the photon provides too much or too little energy. That's sort of like saying if you really under eat or overeat, you won't be able to move around much. In either case, you won't be able to move up in life. And since the energy of a particular photon depends on its wavelength, this means that only precisely matched wavelengths of light will be absorbed by a specific atom.
Now, as you know, if you get an energy or sugar rush, you won't have it for long. You won't be able to work hard and stay excited forever. An excited atom, one with an electron that's moved to a higher energy level, can't stay excited forever either. Excited atoms are unstable, like some people on a sugar rush are just a bit unstable, if you know what I mean. And just like a person eventually crashes after a sugar rush, an excited atom's electron eventually moves down an energy level. As it moves down an energy level, it will release energy equal to the difference between the levels it moves down.
This specific energy is emitted as a photon. A photon that has a unique wavelength that corresponds to that specific amount of energy, meaning the incoming and outgoing photons have the save wavelengths. Since each atom is unique, with unique energy levels, each atom will absorb and emit light with unique wavelengths visible as a color spectrum. This helps astronomers, and scientists in general, identify the elements that make up something, like a distant star.
A spectrum is an arrangement of electromagnetic radiation (which includes visible light) placed in order of wavelength. The color spectrum can reveal patterns of thin, bright, or dark lines, called spectral lines. The use of unique patterns of spectral lines to identify a chemical substance is known as spectroscopy. The way astronomers can use spectroscopy to identify the elements of something like a faraway star's gaseous makeup can be summarized as follows:
An atom's electron is energized by absorbing only a specific kind of incoming photon. The energy of a photon depends on its wavelength. This means a certain atom will only absorb specific kinds of wavelengths. Because the electron doesn't like to be energized for long, it comes back down an energy level very quickly after absorbing this photon. This causes an atom to release, or emit, its energy in the form of a photon, one that has a particular wavelength of light visible on the color spectrum.
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Back To CourseBasics of Astronomy
28 chapters | 325 lessons