The aurora borealis, commonly known as the northern lights, are a splendid sight, with their green, red and purple hues. The lights can be seen in Fairbanks and Interior Alaska for about eight months a year, from mid-August to mid-April.
Here are some answers to some common questions about the northern lights.
Q: What is the aurora?
A: The glow in the sky, known as the aurora borealis, is the result of energetic particles entering the upper atmosphere. The specific glow is different from other forms of brightness in the sky, such as scattered sunlight or lightning. Magnetism within the Earth’s atmosphere guide the energetic particles, most often electrons, along field lines to the high-latitude atmosphere.
As the energetic particles penetrate the upper atmosphere, the chance of colliding with an atom or molecule increases the deeper they go. When a collision occurs, the atom or molecule takes some of the energy of the energetic particle and stores it as internal energy while the electron continues on its path at a reduced speed. The release of that stored energy by an atom or molecule, achieved by sending off a photon, produces light.
Q: What makes the color in the aurora?
A: The composition and density of the atmosphere and the altitude of the aurora determine the possible light emissions.
The atmosphere is made up of varying levels of oxygen and nitrogen. Sometimes the photons emitted by the energetic electrons, creating aurora energy, are strong enough to split the molecules of the air around them into oxygen and nitrogen molecules and atoms. This process gives them the signature colors of nitrogen and oxygen storms. Oxygen atoms typically emit green and red colors.
The overall impression is a greenish-whitish glow. An intense aurora can get a purple edge at the bottom, which is a mixture of blue and red emissions from nitrogen molecules.
Q: What is the altitude of the aurora?
A: The bottom edge is typically at 60 miles altitude, but it extends over a large altitude range. An intense aurora from high-energy electrons can be as low as 50 miles.
Q: How often does the aurora appear?
A: There is always some aurora at some place on Earth. You just can’t always see it. When the solar wind is calm, the aurora might be too high and faint to see.
To see the aurora, the sky must be dark and clear, which is why it’s not visible in the Interior until August.
If you are here then, hope for clear skies and head outside for a look.