Image via Wikipedia

To understand what a corona is, we have to know some things about the sun. To begin with, the sun, at least at its surface, is not a solid like the earth. This surface, which is all that we can observe of the sun, is composed of gases.

In fact, the sun is surrounded by four layers of gaseous matter that hide what is underneath. The  innermost of these layers is called the photosphere. The next two layers are known as the reversing layer and the chromosphere. Together they form the sun’s atmosphere. The outermost layer is the corona.

Let’s see what each of these layers of gas is. The photosphere (or “light sphere”) is what we see when we look towards the sun. Most of the time, dark sunspots can be seen on this bright surface. The “reversing layer”, which is made of gaseous vapours, extends several hundreds miles out from the photosphere of the sun. This layer is never seen, but it can be studied by an instrument called the spectrograph.

Image via Wikipedia

Outside the reversing layer is the chromosphere, our color sphere. It is about nine thousand miles thick and is made up mostly of hydrogen and helium gases. At the time of a total eclipse, it shines out around the dark disc with a brilliant scarlet light. From this red border, flame colored clouds of the same material shoots out to great heights, sometimes even as much as one million miles! They are called prominences, and they look like great flames of fire.

Then comes the outer layer, which is called the corona. It is composed of light, gaseous matter, and has two parts. The inner corona, lying next to the red chromosphere, is a band of pale yellow. The outer corona is white, with streamers extending out millions of miles from the edge of the sun.

All of this describes only the layers that surrounds the sun. What is beneath them still remains a mystery!