Back To CourseBasics of Astronomy
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I think Earth has a magnetic personality. It's beautiful and warm. I even hear this personality is so magnetic that people who see Earth from afar - astronauts - begin to love and nurture Earth even more as they see how beautiful and fragile it is. But enough of the saccharine stuff. Earth really does have some magnetic properties in the astronomical sense. It even has a magnetic tail!
This lesson is all about the outermost part of the Earth's or any other planet's atmosphere, the magnetosphere.
The magnetosphere is filled with just a tiny bit of plasma, but it's dominated by the Earth's magnetic field. Plasma is ionized gas made up of positively-charged ions and negatively-charged electrons. Some of these ionized gases come from Earth's upper atmosphere and others from solar wind particles. The solar wind is a stream of plasma emitted by the sun.
The magnetosphere loves to trap energetic charged particles in regions called Van Allen belts. They are two doughnut-shaped areas centered on the equator where, like a magnet traps metal, the Earth's magnetic field traps charged particles. The outer Van Allen belt, lying about 15,000 kilometers above the surface of the Earth, contains electrons. The inner belt, lying approximately 2,500 kilometers above the Earth's surface, contains protons.
While the diagram on the screen makes it seem like these belts are separate, in reality, they gradually merge with one another. This means the inner belt's energetic protons decrease in number as it merges with the outer belt.
Now, while the magnetosphere has some plasma, there's another kind of plasma I mentioned before, that of the solar wind, which interacts with the magnetosphere. You see, the solar wind rushes from the sun and towards our planet like a stream of water may rush towards an object, like a tree during a flood. As this water rushes towards the tree, you can clearly tell how this sort of bowing effect takes place in front of it.
Well, as the solar wind comes close to the magnetosphere, it begins to slow down, like water slows down in the space in front of the tree. The area of space where the solar wind slows down as it approaches the Earth's magnetosphere is called the bow shock.
Internal to the bow shock is the magnetopause, the outer boundary of the magnetosphere. It's a roughly 100 to 200 kilometer thick boundary between the magnetosphere and solar wind.
The solar wind will flow around the Earth's magnetosphere on the sunward side, the side the solar wind is coming from. This flow will actually compress the magnetosphere on the sunward side.
However, on the night side of Earth, a magnetotail will form. This is part of the magnetosphere located behind a planet that is stretched by the solar wind. It sort of looks like that tail that extends behind the tree, opposite the side from where the water is crashing into it.
Knowing all of this, another way to think of the magnetosphere is as a teardrop-shaped cavity or void in the solar wind, as the solar wind's particles are inconveniently forced to flow around the Earth.
Energy that's carried by this solar wind gets transferred to the charged particles that make up the magnetosphere itself. Like eddies and currents form right behind a tree as water flows past it, it is mainly in the magnetotail where the solar wind creates currents of electrons, that this energy transfer occurs. These currents of high energy electrons make their way into Earth's upper atmosphere close to the Earth's magnetic poles.
Around 100 kilometers (60 miles) above the surface of the Earth, these electrons collide with atoms and molecules in our atmosphere, such as hydrogen, helium, oxygen, and nitrogen. Such collisions result in the emission of different colors, such as red or green when oxygen is excited, red and violet when nitrogen is excited, and blue and purple when hydrogen and helium are excited. We term this glow either as aurora borealis, 'northern lights,' or the aurora australis, 'southern lights.'
Maybe you're wondering how an atom or molecule can produce light. Well, let's say a batter strikes a baseball for a home-run. What does the crowd do? They jump up, higher, off of their seats in excitement. When a high-energy particle strikes an atom or molecule, its energy is transferred to the atom in our example, and electrons in the atom jump up to a higher energy level because they're so excited!
Eventually, when the fans have released all of their energy from excitement, they sit back down. Like an excited fan, an excited atom can't stay excited forever, and they release their excess energy. This happens when the electrons sit back down to their lower energy level. When they do this, their excess energy is released as radiation, electromagnetic radiation that we see as a particular color or beam or wavelength of visible light. Because every gas has a particular collection of energy levels, each gas will give off a particular color, just like every screaming and excited fan has a different sound to their voice.
You can sit back down now from the excitement of this lesson. Let's try to remain calm as we review everything.
The outermost part of the Earth's or any other planet's atmosphere is the magnetosphere. The magnetosphere is dominated by the Earth's magnetic field, but it also contains a very thin amount of plasma. Plasma is ionized gas, made up of positively-charged ions and negatively-charged electrons. The magnetosphere holds on to its energetic particles in its Van Allen belts. The inner belt traps protons, and the outer one traps electrons.
Plasma of the solar wind interacts with the magnetosphere, as well. The area of space where the solar wind slows down as it approaches the Earth's magnetosphere is called the bow shock. Internal to the bow shock is the magnetopause, the outer boundary of the magnetosphere.
On the night side of Earth, a magnetotail will form. This is part of the magnetosphere located behind a planet that is stretched by the solar wind. It is namely in the magnetotail where currents of energetic electrons are whipped up in the magnetosphere by the solar wind. These electrons then interact with atoms in the Earth's atmosphere near the magnetic poles to produce the aurora borealis, 'northern lights,' or the aurora australis, 'southern lights.'
Finish this lesson on the magnetosphere, then:
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Back To CourseBasics of Astronomy
28 chapters | 325 lessons