Solar Magnetism

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Solar Magnetism


the aggregate of the phenomena associated with the existence of a magnetic field on the sun. Various magnetic fields are distinguished: the magnetic fields of sunspots, the magnetic fields of active regions outside the sunspots, and the general magnetic field of the sun.

A magnetic field on the sun was first discovered by the American astronomer G. Hale in 1908 from the splitting of absorption lines in the spectra of sunspots (seeZEEMAN EFFECT). Strong magnetic fields are usually measured through the use of a circular-polarization analyzer, which permits the Zeeman components of a line to be observed separately. For a weak magnetic field, measurements with a solar magnetograph are most accurate.

Solar magnetism may be the cause of the heating of the upper solar atmosphere, the acceleration of particles, and their ejection into interplanetary space. A determining role is played by solar magnetism in many phenomena of solar activity, for example, in solar flares. Weak magnetic fields are associated with regions of elevated brightness where gas is heated. Local intensification of the magnetic field above 1,400 oersteds (Oe), however, leads to cooling of the gas and to the formation of sunspots. Sunspots have the strongest magnetic fields (up to 5,000 Oe). These fields obey certain laws governing the change in their polarity with the solar-activity cycle; the length of the magnetic cycle is two 11-year cycles of solar activity, that is, approximately 22 years. The interaction of magnetic fields in sunspot groups is apparently responsible for solar flares. Outside the active regions, weak magnetic fields called background fields are observed. Together with the active regions, they basically determine the structure of the solar corona and the interplanetary medium.

At heliocentric latitudes above 55°, the general magnetic field, which is similar to a dipole field, is measured. Temporary fluctuations are characteristic of the general magnetic field; in some years its distribution with respect to latitude differs sharply from a dipole distribution. The magnetic field has been shown to change sign at the poles at times of maximum solar activity. The Soviet astronomer A. B. Sevemyi has studied the fine structure and statistical character of the general magnetic field. It is concentrated in individual structural elements that have different dimensions and a bipolar magnetic field with a strength of up to approximately 20 Oe. The strength of the averaged general magnetic field is 1–5 Oe.

The overall magnetic field of the entire sun as a star varies with a period of about 27–28 days and an amplitude of approximately 1 Oe. The field usually has two or four sectors of alternating polarity that coincide with the sector structure of the interplanetary magnetic field. The nature of solar magnetism has not yet been thoroughly investigated.


Sevemyi, A. B. “Magnitnye polia Solntsa i zvezd.” Uspekhi fizicheskikh nauk, 1966, vol. 88, issue 1.
Solar Magnetic Fields. Edited by R. Howard. Dordrecht, 1971.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Each pearl is a cross-section of an intense, single fiber of the Sun's magnetic field - the basic building block of the solar magnetism," he said.
Other planets such as Jupiter, Mars and Venus also play a part because their magnetic fields affect solar magnetism.
Some records show that six out of seven cold spells over a 5,000-year period coincided with long-term lulls in solar magnetism. Going back 10,000 years, records from Scandinavia found the same links in 17 out of 19 cold spells.
A period of roughly 2,200 years is suggested by records of solar magnetism from the radiocarbon abundance in bristlecone-pine tree rings that can be traced over several millenniums.
They can be measured in the laboratory from tree rings and ice cores, yielding the history of solar magnetism. Both isotope records confirm that the sharp decrease of sunspots in the 17th century, the Maunder Minimum, indeed matched a very low level of solar magnetic activity.
"The amount of carbon-14 in trees over time maps the history of solar magnetism," she says, and "the tree rings thus provide a timeline of the magnetic history of the sun." One well-known period of low solar magnetism identified from tree-ring studies is the Maunder minimum, which lasted from about A.D.