Stable auroral red (SAR) arc emission observed over North America from space by the Dynamics Explorer 1 satellite.
Click on image for full size
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.


You might also be interested in:

Cool It! Game

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

AU

AU stands for Astronomical Units. It is a useful way to measure the distances in interplanetary space. It is the distance between the Earth and the Sun, which is about 93 million miles. For reference,...more

The Spiral of the IMF

The solar wind is formed as the Sun's top layer blows off into space, carrying magnetic fields still attached to the Sun. Gusts form in the solar wind associated with violent events on the Sun. Particles...more

Spiral Path of Material

For a planet to be affected by a blob of material being ejected by the sun, the planet must be in the path of the blob, as shown in this picture. The Earth and its magnetosphere are shown in the bottom...more

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....more

The Effect of Aurora on the Atmosphere

This figure shows the effect of the aurora on the atmosphere. When FAC's enter the atmosphere and create the aurora, they heat the atmosphere suddenly and abruptly. This creates an impulse which travels...more

The forming Aurora

This picture shows the flowing of particles into and out of the auroral zone, as Field-Aligned currents (FAC's) take at short-cut through the atmosphere. Some of the particles entering the auroral zone...more

The Expanding Auroral Oval

This figure shows a series of images of the auroral oval as it expands over the course of about an hour in response to a geomagnetic storm. This is an animation of the auroral oval expanding....more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA