This is a SAR arc 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
If someone says they saw an aurora, you might picture something like this. There is another type of aurora that we can't see. These aurora are called SAR arcs. The SAR stands for Stable Auroral Red. That basically means that pictures taken of these aurora by special instruments (remember, we can't see these aurora) show a soft glow of red light.
SAR arcs happen about 10% of all nights. So if you're really smart, you can say to your parents while looking up at the night sky, "hey, what's that?" When they don't answer because they don't see anything special, you can say, "maybe it's just an invisible SAR arc!"
Shop Windows to the Universe Science Store!
Our online store
on science education, classroom activities in The Earth Scientist
specimens, and educational games
You might also be interested in:
AU stands for Astronomical Units. It is an easy way to measure large distances in space. It is the distance between the Earth and the Sun, which is about 93 million miles. For really big distances, we...more
The solar wind is formed as the Sun's top layer blows off into space. It carries magnetic fields still attached to the Sun. Streams appear to flow into space as if they are spiraling out from the Sun,...more
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
If someone says they saw an aurora, you might picture something like this. There is another type of aurora that we can't see. These aurora are called SAR arcs. The SAR stands for Stable Auroral Red. That...more
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
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
This picture shows a series of images of the auroral oval as it expands over the an hour's time because of a storm on the Sun. This is an animation of the auroral oval expanding....more