Seeing as how it's snowing again and looks like it's going to be too cloudy to observe for quite some time, I though this might be a good time to talk about weather - space weather, that is.
What is space weather? For the most part it's the Sun throwing stuff at us, and by stuff, I mean charged particles. The Sun is a giant ball of hydrogen and helium gas (to get a sense of the size, imagine shrinking the Earth down to the size of a peppercorn - on that scale the Sun is the size of a basketball) that has a surface temperature of nearly 10,000 degrees Fahrenheit. The gas is so hot that most of the atoms have lost their negatively charged electrons, leaving positively charged ions. At the surface of the Sun these ions are constantly flying off into space creating the solar wind. This isn't a wind like we experience on Earth, but rather a continual flow of these charged particles.
The Earth is surrounded by a magnetic field, and that field acts like a shield against the solar wind. The charged particles can't pass through the field, and are forced to flow around the field. But near the north and south magnetic poles there are "holes" in the magnetic field (see figure), and at these locations the particles leak inside the field where they become trapped in two belts surrounding Earth, call the Van Allen belts (the blue "ears" on either side of Earth in the figure). When two many particles are trapped in the belts, they start to overflow, and the particles stream into the atmosphere around the north and south poles.
The most common yellow-green color results from oxygen atoms being struck by medium energy particles, while red auroras are caused by high energy particles colliding with nitrogen.
What is space weather? For the most part it's the Sun throwing stuff at us, and by stuff, I mean charged particles. The Sun is a giant ball of hydrogen and helium gas (to get a sense of the size, imagine shrinking the Earth down to the size of a peppercorn - on that scale the Sun is the size of a basketball) that has a surface temperature of nearly 10,000 degrees Fahrenheit. The gas is so hot that most of the atoms have lost their negatively charged electrons, leaving positively charged ions. At the surface of the Sun these ions are constantly flying off into space creating the solar wind. This isn't a wind like we experience on Earth, but rather a continual flow of these charged particles.
The Earth is surrounded by a magnetic field, and that field acts like a shield against the solar wind. The charged particles can't pass through the field, and are forced to flow around the field. But near the north and south magnetic poles there are "holes" in the magnetic field (see figure), and at these locations the particles leak inside the field where they become trapped in two belts surrounding Earth, call the Van Allen belts (the blue "ears" on either side of Earth in the figure). When two many particles are trapped in the belts, they start to overflow, and the particles stream into the atmosphere around the north and south poles.
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| Solar wind flowing around Earth's magnetic field |
When this happens, we see the beautiful Aurora, or Northern and Southern lights. Charged particles colliding with gasses in the atmosphere cause those gasses to glow. The different colors of the aurora come from the different gasses in the atmosphere and the energy of the charged particles.
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| The Northern Lights (Image from theguardian.com) |
Like the weather we experience here on Earth, space weather sometimes experiences storms. The surface of the Sun is a very violent and chaotic place. Occasionally a bubble of gasses will "pop" off the surface of the sun and fly off into space (a bit like the bubbles in a pot of boiling liquid). This is called a solar flare, or if it's a really big bubble of gas, a coronal mass ejection. These things can be several times larger than Earth! When one of these bubbles of gas heads for Earth, we're in for a storm! We can expect to see very active auroras, sometimes extending down to lower latitudes. These storms put a lot of energy into the atmosphere and that energy can sometimes disrupt power transformers and shut down power in entire regions (this happened in Quebec in 1989). They're also a danger to satellites and astronauts. The good news is, it takes about three days for solar material to reach Earth and there are several satellites that continually watch the Sun and look for dangerous solar storms. When we see a storm coming, we can protect our satellites, power stations, and astronauts from damage. And then we can go outside and enjoy natures fabulous light show!
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