The Aurora Borealis, also known as the Northern Lights, are an amazing natural phenomenon that involves the Sun, the Earth’s core, and the Earth’s atmosphere.
Let’s start with the Sun. Our Sun is a star that emits heat and light, but it also emits a constant stream of charged particles. These charged particles consist of negatively charged electrons and positively charged atoms streaming through space at about one million miles per hour! Collectively, these charged particles streaming from the Sun is called the solar wind. The solar wind is always present, but there are times when the solar wind is more active and more energetic. This occurs when the surface of the Sun is more active with solar storms that can eject above average amounts of heat, light, and charged particles into space. Regions of the Sun where solar storms are currently present can located by looking for solar prominences, solar flares, and sunspots.
If the solar wind were to constantly interact with the Earth’s atmosphere, it would be disastrous. The solar wind would strip away a significant portion of the atmosphere in about 1000 years, leaving the Earth with a wispy atmosphere like Mars and unable to support life on Earth as we know it. But the Earth has a mechanism that protects the Earth from the solar wind – it’s magnetosphere. The magnetosphere is a magnetic field that surrounds the Earth, and it doesn’t so much have a sphere-shape as it has a warped bubble-like shape that is a squashed on the side of the Earth facing the Sun and a long tail on the side of the Earth away from the Sun. The magnetosphere is generated by the outer liquid iron core that surrounds the inner solid iron core of the Earth. This super-hot and electrically charged iron in the liquid core rotates around the center of the Earth, acting like a dynamo and generating a magnetic field.
As the solar wind interacts with the magnetosphere, the magnetosphere protects the Earth by redirecting the charged particles harmlessly away from the atmosphere. But the shape of the magnetosphere does have a couple of “soft spots” where charged particles can get close enough to interact with upper atmosphere of the Earth. These soft spots are located at the magnetic north and south poles of the Earth, which are near but not exactly at the same locations as the geographic north and south poles. There are not enough charged particles entering these soft spots to cause any permanent damage to the atmosphere, but when they do interact, they energize the oxygen and nitrogen in the atmosphere, causing them to fluoresce, and producing what we in the northern hemisphere call the Northern Lights. The lights generated near the south magnetic pole are called the Aurora Australis, or the Southern Lights.
The colors of the lights are determined by the altitude of the elements in the atmosphere being fluoresced, and how far from the magnetic poles these lights can be seen are determined by the activity of the Sun. Our Sun is particularly active right now, so the Northern and Southern Lights can be seen more often and at latitudes closer to the equator.
If you would like to learn more about the Sun, the Earth, aurora, and other amazing objects and phenomena out in our Universe, come visit your local planetarium! www.wsc.edu/planetarium
