The green lights above the Earth's surface are the aurora as seen from the International Space Station on July 25, 2010. (Click for larger version.)
Credit: Image Science & Analysis Laboratory, NASA Johnson Space Center
Have you ever seen the dazzling, dancing lights of the aurora? Only visible at high latitudes, and at certain times, not everyone can see the aurora. However, photographs let us all know what it looks like. For example, the photograph at right shows what the aurora looked like from the International Space Station on July 25, 2010.
Over a century ago, on January 5, 1892, German physicist Martin Brendel successfully took a photograph of the aurora in northern Scandinavia. The photo was black and white and it wasn’t very clear, but when the photo was printed in a magazine it gave many people their first glimpse of an aurora.
After taking the photo, Martin Brendel spent two months living at the Arctic Circle during the darkest and coldest part of the year in order to study the science of the aurora. Today we know that these breathtaking displays of color are a natural interplay between the solar wind and Earth's atmosphere. Here’s how it works:
Our Sun generates a strong solar wind, which carries about one million tons of plasma (electrons, protons, and other particles) away from the Sun every second. The plasma is hot - nearly 200,000 degrees Fahrenheit (about 100,000 degrees Celsius).
When the solar wind flows past the Earth, it crashes into and flows around our planet's magnetic field. Some of the electrically charged particles move inward, toward the stronger field and become trapped in the Earth's inner magnetosphere. They bounce from the North Pole to the South Pole and back again. Atoms and molecules in the atmosphere hold onto extra energy when the solar wind particles bump into them. With this extra energy the atoms and molecules are in an excited state. When the atoms and molecules "de-excite," they release the extra energy, which creates bright colored light at high altitudes. We call this phenomenon the aurora borealis in the Northern Hemisphere. It’s also known as the Northern Lights. In the Southern Hemisphere it’s known as the Southern Lights or aurora australis.
- Teachers: Check out the Sun Teaching Box for curriculum that gets students exploring our star.