5. A Magnetic Star

A Magnetic Star

The entire Sun is a giant mass of incandescent gas, unlike anything we know on Earth. The Sun has no surface; its gas just becomes more tenuous the farther out you go. Although we cannot see it with our eyes, very diffuse solar gas extends all the way to the Earth and beyond.

The diaphanous solar atmosphere includes, from its deepest part outward, the photosphere, chromosphere and corona. The Sun’s magnetism plays an important role in molding, shaping and heating the coronal gas.

The visible photosphere, or sphere of light, is the part of the Sun we can watch each day. It is the level of the solar atmosphere from which we get our light and heat. The photosphere contains sunspots, thousands of times more magnetic than the Earth, and the number and position of sunspots varies over the 11-year cycle of solar magnetic activity.

The visible sharp edge of the photosphere is something of an illusion. It is merely the level beyond which the gas in the solar atmosphere becomes thin enough to be transparent. The chromosphere and corona are so rarefied that we look right through them, just as we see through the Earth’s clear air.

The chromosphere is very thin, but the Sun does not stop there. Its atmosphere extends way out in the corona, to the edge of the solar system. The corona’s temperature is a searing million degrees Kelvin, so hot that the corona is forever expanding into space.

The entire solar atmosphere is permeated by intense magnetic fields generated inside the Sun, rooted in the photosphere, and extending into the chromosphere and corona.

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Copyright 2010, Professor Kenneth R. Lang, Tufts University