Solar Magnetic Fields

Magnetism is the key to understanding the Sun. Magnetism, or magnetic field, is produced on the Sun by the flow of electrically charged ions and electrons. Sunspots are places where very intense magnetic lines of force break through the Sun's surface. The sunspot cycle results from the recycling of magnetic fields by the flow of material in the interior. The prominences seen floating above the surface of the Sun are supported, and threaded through, with magnetic fields. The streamers and loops seen in the corona are shaped by magnetic fields. Magnetic fields are at the root of virtually all of the features we see on and above the Sun. Without magnetic fields the Sun would be a rather boring star.

Measuring Magnetic Fields

Magnetic forces change the direction of motion of moving charged particles like electrons. Because of this, electrons that orbit around a nucleus in one direction will have more energy than electrons that orbit about the nucleus in the opposite direction. This allows us to remotely measure the Sun's magnetic field by observing the difference in the energy of the light emitted as these electrons jump from orbit to orbit. With the proper instrumentation we can determine both the strength and the direction of the magnetic field all across the surface of the Sun.

Modeling Magnetic Fields

Magnetic field lines loop through the solar atmosphere and interior to form a complicated web of magnetic structures. Many of these structures are visible in the chromosphere and corona, the outermost layers of the Sun's atmosphere. However, we usually measure the magnetic field itself in the photosphere, the innermost layer of the Sun's atmosphere. Techniques can be used to mathematically map these magnetic field lines into the outer layers where they can be compared with the observed structures.

Predicting Space Weather

A better understanding of the Sun's magnetic field and its behavior will allow us to make better predictions of space weather. Observations of magnetic fields associated with solar flares show that flares are likely to occur when the magnetic field lines linking two sunspots become sheared or twisted. Observations of the Sun's magnetic field over the last 20 years illustrates its behavior over two sunspot cycles. However, predicting long-range behavior, such as the size of the sunspot cycle, is still based on observing trends and patterns. We hope that in the near future we will understand the Sun well enough to make these predictions based on current conditions and past history using a mathematical model of the actual processes.  (Source: "The Key to Understanding the Sun" from Solar Physics, NASA's Marshall Space Flight Center.)

Topic Image Source

"Deep Roots of the Solar Wind" - The Sun's atmosphere is threaded with magnetic fields (yellow lines). Areas with closed magnetic fields give rise to slow, dense solar wind (short, dashed, red arrows), while areas with open magnetic fields -- so-called "coronal holes" -- yield fast, less dense solar wind streams (longer, solid, red arrows). In addition to the permanent coronal holes at the Sun's poles, coronal holes can sometimes occur closer to the Sun's equator, as shown here just right of center. (Source: 2003 September 18 image from the SOHO Extreme ultraviolet Imaging Telescope (EIT). ESA/NASA.)