What's the strangest thing about our Sun?

The outermost layer of our Sun is a real puzzle. This layer is known as the corona (the "crown"). Because the surface of the Sun (the photosphere) is so bright, we normally can't see the faint corona.

X Ray Image of Sun

Solar Eclipse Image

Photograph of X-Rays
coming from the Sun

Photograph taken during eclipse
showing solar corona

The corona is millions of degrees hotter than the surface of our Sun. The mystery is that astronomers don't know why the corona is so hot!!!

One way the corona can be studied is by using X-ray sensing satellites. This is because the corona is the only layer of the Sun that is hot enough to emit X-rays. The picture on the left comes from the Yohkoh Satellite.

Another way to look at the corona is to artificially block the bright light of the photosphere, to create the same effect as an eclipse. This is done using an instrument called a coronagraph, which produces images similar to that shown above on the right. Using a coronagraph means that we don't have to sit around and wait for solar eclipses.

Coronagraphs allow us to see only the outer parts of the corona, because the instrument blocks our view of the inner corona. X-ray images can show us the parts closer to the Sun, because there's no need to block out the solar disk.

More info:

At the end of this tour why not check out some links to more technical descriptions of the different layers of the Sun?

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Image Credits:
X-Ray Sun: Yohkoh Science Team
Solar Eclipse: HAO/NCAR