Stable auroral red (SAR) arc emission observed over North America from space by the Dynamics Explorer 1 satellite.
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Image provided courtesy of L. Frank and J. Craven from the Dynamics Explorer 1
The SAR Arc
The aurora we are most familiar with is the polar aurora. This is what people are talking about when they say the northern or southern lights. But there are other less-known aurora, such as SAR arcs. The SAR arcs or Stable Auroral Red arcs were discovered in 1956.
The reason that SAR arcs were discovered so late compared to polar aurora is that SAR arcs aren't usually visible. So, humans have to use instruments to tell that they are there (see image to left). SAR arcs can stretch across the entire sky.
Scientists have only known that SAR arcs existed for last 50 years. So, there are still debates as to exactly what produces SAR arcs. It is likely that this faint red glow is caused by the release of energy by the Earth's ring current system.
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