The Universe and Galaxies: The Sun – Magnetic fields and Solar Wind

Discovery Space: Magnetic fields and Solar Wind

The sun’s influence extends far into space. The complex magnetic field of the sun changes continuously within cycles that last several years. These are tied into various phenomena, such as the formation of sunspots.

The hot plasma (gas) of the sun consists of electrically charged particles. The sun rotates faster near its equator than it does near its northern and southern latitudes, and hot plasma rises from the center toward the surface during this rotation, creating electrical currents. These form magnetic fields over the sun, which in turn feed back and affect the electrical currents, resulting in a complex interaction of influences.

The consequence of these processes together is that the magnetic fields of the sun are continuously changing shape. Sometimes, they are similar to those of the Earth, in that the field lines run straight from pole to pole. At other times, due to the sun’s uneven rotation speeds between the equator and poles, the fields become more and more twisted, resulting in their effects being amplified a thousand- fold in several regions of the surface.

Magnetic field lines emerge in these areas, known as sunspots, while retreating in others. Sunspots appear darker in comparison to their surroundings because the emerging magnetic fields block the rising plasma, causing patches of cooler temperature where less energy is being transported to the surface from the interior.

Some plasma is guided along the magnetic field lines creating filaments; these enormous protuberances consist of the sun’s material and can last anywhere from hours to months. When viewed against a dark background they appear as huge prominences that flare outward and loop back toward the surface.

The sunspot cycle

The total number of sun- spots depends on the distortion cycle of the solar magnetic field. During a sunspot minimum, when field lines are straight, there are almost no visible sun- spots. As the fields twist over a period of about 11 years, more develop until the sun-spot maximum, the point at which the solar magnetic field reverses polarity and straightens out.

The previously magnetic north pole is now the magnetic south pole and vice versa. A full cycle of magnetic repolarization therefore includes two sunspot cycles and takes about 22 years.

Solar wind

The thin outer layer of the sun, the corona, reaches far into space. Due to its extreme heat, the sun’s matter is continuously released as solar wind. This wind mainly consists of protons, electrons, and helium nuclei, which are found between the Earth and the sun.

Solar wind often reaches speeds of about 250 miles per second (400 km/s), and sometimes double this. It creates its own magnetic fields, which deform the shape of both the sun and the Earth’s magnetic fields.


THE SUN has a ratio of one million hydro- gen nuclei to 98,000 helium nuclei, and several hundred nuclei of heavier elements.

About 72 percent of the solar mass accounts for the hydrogen mass and about 26 percent for the mass of helium.

EVERY SECOND, the sun loses a mass of about one million metric tons (one billion kg) due to solar wind.