The Evolution of Sunspots: Changes in Morphology and Magnetic Field Strength Over Time

A series of images of the Sun taken at NSO (Sunspot, NM) during the period March 7-17 1989 shows the evolution of a sunspot group as it moves around the Sun. The upper sequence, taken in white light, shows the more usual representation of the solar surface. Below, the same sunspot region is followed from magnetogram studies, where black and white regions show different magnetic polarity. The correspondence between morphology and magnetic activity is evident.


The atmosphere is the Sun is a maelstrom of hot gases, charged particles, and magnetic fields. Earth is affected not only by light from the Sun, but also by ejection of the solar wind and huge masses of energetic particles that buffet Earth’s magnetosphere, sometimes wreaking havoc on our sensitive electrical systems. Variations in the Sun’s cycle also profoundly influence Earth’s weather. While astronomers have made great advances in recent years in their understanding of magnetism as the heart of most solar processes, many important connections pertaining to the Sun’s magnetic field remain a mystery. For example, how does the morphology and magnetic fields strengths of sunspots influence the evolution of sunspots? How do these quantities change over time?


Sunspots are the host of most solar eruptions because of their strong and complex magnetic nature. They indicate the magnetic activity level of the Sun. Detailed studies of sunspots not only are necessary for understanding the basic principle of magnetic field evolution in the Sun, but also may provide clues on how the energy builds up and is transported during solar eruptions.

The research question being asked at the McMath-Pierce solar telescope and with the solar archival data:

What is the short and long term evolution of sunspots?

The way we are going to address the question is by studying sunspot morphology and magnetic field strength on short (a few days) and long (a couple weeks) timescales. Ultimately it is the study over timescales of years, which contributes best toward the understanding sunspot evolution—a study your students may wish to undertake back in your classroom!

Why are we interested in the question asked above? Because solar scientists are interested in answering:

In this project, you will take infrared spectra of sunspots using the McMath-Pierce solar telescope, the largest in the world. You will examine lines split by the Zeeman Effect to determine the spatial and temporal changes in the near-surface solar magnetic field. Your data will be added to an archive of solar images that you will use to investigate the growth and decay of sunspots and the relation of magnetic field strength to sunspot properties, among a couple of other projects. The database of solar images includes maps of the magnetic field strength, the continuum data, and the velocity field. Join us as we examine the evolution of sunspots by studying the changes in their morphology and magnetic field strength over time.

Solar Data

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The Astronomy RBSE program is administered by the National Optical Astronomy Observatory with funds from the National Science Foundation.