The Sun

Red sunspots on orange sun

The Sun with lots of sunspots as viewed by a NASA satellite in March 2001.


The Sun is the closest star to Earth and is the center of our solar system. A giant, spinning ball of very hot plasma (electrically charged gas), the Sun is fueled by nuclear fusion reactions. Light from the Sun heats our planet and makes life possible.

The amount of light emitted by the Sun is surprisingly steady, varying by less than 1/10th of one percent over periods spanning decades. However, the Sun is not perfectly constant and unchanging. Powerful magnetic disturbances within the Sun produce exotic features such as solar prominences and coronal loops. Sunspots, indicators of strong magnetic fields, come and go in cycles lasting many years. Explosive solar storms, called solar flares and coronal mass ejections (CME), are more common when the Sun's magnetic field is most disturbed at the peak of the sunspot cycle when the spots are plentiful.

Although the Sun doesn't have a solid surface like Earth, scientists still speak about the "parts" or regions of the Sun, including it's surface, interior... and atmosphere! Yes, the Sun has an atmosphere! In fact, the outer atmosphere of the Sun extends millions of kilometers into space, beyond the orbits of Earth and the other planets. Our home planet actually orbits within the atmosphere of a star!

The Sun continuously emits vast quantities of energy as light and other forms of electromagnetic radiation. It also gives off large amounts of matter as particle radiation, mostly in the form of high-energy protons and electrons. This outward flow of particle radiation is called the solar wind. Often when explosions erupt on the surface of the Sun, huge "space weather storms" flow outward with the solar wind, sometimes crashing into Earth. Some of these storms can play havoc with human technologies, but can also produce the beautiful displays of color we call the aurora or Northern and Southern Lights.

© 2012 UCAR