The document summarizes research on the heights of auroras (Northern Lights). It discusses: 1) Early 20th century scientists like Carl Størmer used parallax measurements between observers dozens of kilometers apart to calculate that most nighttime auroras occur between 90-150 kilometers above the Earth. 2) Auroral colors are affected by altitude, with green occurring highest around 120-180km and red occurring even higher, while blue and violet are below 120km. 3) Auroras are caused by collisions between charged solar particles trapped by Earth's magnetic field and atmospheric gases, which emit light as the particles lose energy.

1. Sothern Lights Aurora Australis Presented by Ethan Ross & Tyler Goss

6. Based on more than 20.000 parallactic auroral pictures, aforementioned Størmer and his assistants accurately calculated the average height of the auroras. Most of the night-time auroras within the auroral zones are found between 90 and 150 kilometers. A few auroras may extend up to roughly 500 kilometers . Average altitude is between 100 and 120 kilometers. Average size

7. Altitude affects auroral colour. The strong, green light originates at altitudes of 120 to 180 kilometers. Red northern lights occur at even higher altitudes, while blue and violet occur mostly below 120 kilometers. When the sun is "stormy", red colour occur at altitudes between 90 to 100 kilometers. Entirely red northern lights are sometimes seen, particularly at lower latitudes, and are often mistaken for a fire on the horizon. The main point in the auroral theory is that electrically charged particles excite the atmospheric gases, that is, the electrons begin to circle the nucleus in a different orbit because of an excess of energy. The excited particle is unstable and will give up its excess energy by emitting light. This is what is called aurora. Colours

8. Sound waves are pressure waves which travel about 340 meters per second in air at ground level. At altitudes between 80 and 500 kilometers, where the aurora occurs, we have a near-vacuum, so it is not possible for sound waves to propagate. But since there are a lot of reports of crackling sounds during an aurora display, there may be some sort of physics behind it. Sound

9. Some can last for hours, days, weeks or months depending on the intensity and size of the solar flare. Length

10. http://www.northern-lights.no/english/ http://www.wikipedia.org/ http://www.northern-lights.no/english/what/altitudes.shtml