Solar Sunspots and Flares

The high magnetic fields in the sunspot-producing active regions also give rise to explosions known as solar flares.  When the twisted field lines cross and reconnect, energy explodes outward with a force exceeding that of millions of hydrogen bombs.

Temperatures in the outer layer of the sun, known as the corona, typically fall around a few million kelvins.  As solar flares push through the corona, they heat its gas to anywhere from 10 to 20 million K, occasionally reaching as high as a hundred million.

Because solar flares form in the same active regions as sunspots, they are connected to these smaller, less violent events.  Flares tend to follow the same 11-year cycle. At the peak of the cycle, several flares may occur each day, with an average lifetime of only 10 minutes.

Classification of Solar Flares - NASA/Goddard Space Flight Center


Solar Minimums and Maximums

Solar minimum is the period of very low solar activity of the sun. During this time, sunspot and solar flare activity diminishes, and often do not occur for days at a time.  Solar maximums are periods of great solar activity when there may be hundreds of sunspots.

Early records of sunspots indicate that the Sun went through a period of inactivity in the late 17th century. Very few sunspots were seen on the Sun from about 1645 to 1715.

Sunspot Activity

Although the observations were not as extensive as in later years, the Sun was in fact well observed during this time and this lack of sunspots is well documented.  This period of solar inactivity also corresponds to a climatic period called the "Little Ice Age" when rivers that are normally ice-free froze and snow fields remained year-round at lower altitudes.  The connection between solar activity and terrestrial climate is an area of on-going research.

The Sun Over The Last 48 Hours
Student Project Solar Observation Classroom Activity.
For lesson plans involving the sun and SOHO, click here.