Atmosphere on the Sun

by Jeanette Cain

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The Sun's surface, or photosphere, normally hides the faint, thin solar atmosphere, and can only be seen during a total eclipse. Once the Moon passes in front of the Sun, it's atmosphere is made visible to those on Earth. The chromosphere and the corona are the two main regions of the Sun's atmosphere, and have not only explosions, but huge explosions called flares and prominences. The corona is hundreds of times hotter than the photosphere, resulting in the Sun's atmosphere evaporating at a million tons every second into the surrounding space.

The corona, the Sun's outermost region, extends millions of kilometers into space, and is above the chromosphere. Its temperature may rise above three million degrees Centigrade, even when the corona seems to be faint, due to the thinness of the gas. Billions of tons of gas are held within bubbles that erupt from the corona, which bubbles send shock waves into the solar wind.

Earth receives solar winds at speeds from three hundred to eight hundred kilometers per second. The magnetic field on Earth will deflect most of the solar wind, but a trade-off is made-the field becomes squeezed and drawn into a lengthy tail.

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The chromosphere is just above the photosphere, and consists of a dense layer of helium and hydrogen gas, about 5,000 kilometers thick. The temperature closer to the photosphere is around 4,000 degrees Centigrade, but over 500,000 degrees Centigrade at the top area when merging with the corona. The chromosphere sends gas and spicule jets into the corona, where they are lifted from the edges of the convection cells of hot gas from the Sun's interior, and then withdraws beneath the surface.

A release of magnetic energy from explosions in the chromosphere are called solar flares. These emissions of high-energy particles and radiation are bursting with interference for radio communications (also dangerous to space astronauts) on the Earth as they hit the ionosphere. The ionosphere is Earth's electrically charged atmospheric layer. When solar wind particles become trapped by the magnetic field on Earth, and collide with air molecules in the upper atmosphere, the aurora becomes the star of the show. The auroras are the colored lights over Earth's magnetic poles.

In 1990, NASA launched Ulysses for the ESA (European Space Agency) to study the solar wind. Its orbit will be over the Sun's polar regions for detecting high-speed particle streams not usually making it to Earth. In 1995, SOHO (Solar and Heliospheric Observatory) was launched by ESA-NASA to observe the corona and solar oscillations about 1.5 million kilometers from Earth. TRACE (Transition Region and Coronal Explorer) was launched in 1998 by NASA for study of the corona and the boundary between the corona and the chromosphere.


1. Couper, Heather and Nigel Henbest. Space Encyclopedia DK Publishing, Inc.: NY 1999

2. Editors. Secrets of the Universe. International Master Publishing: US. 1999