In the outermost zone of the Sun there is an area that could be considered as its surface. It does not have a well defined limit, and is formed by a region hundreds of kilometers thick, called photosphere. In the image we can contemplate this area of the solar surface.
The photosphere is the last layer of the star, which we see when we look at the Sun. It is opaque and bright. The drop in density in this area is very fast, so the contours of this region are very regular. It is the reason that the image offered by the solar star has a perfectly defined contour, instead of blurred boundaries.
Despite this, the surface of the Sun is not uniform. In the high resolution image we can verify that the photosphere has a grainy appearance. It consists of millions of grains with an average size of a thousand kilometers, whose life is only a few minutes.
The short life of these grains is due to convection in the layers close to the surface. From the depths of the sun springs hot gas that reaches the surface and grains. The gas, with a temperature above 300 degrees, spreads over the entire surface, cooling at the same time, and then submerges again. This temperature difference is what gives the sun its granular appearance.
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