Researchers compile a 45-year map record of sunspots
A dark, snaking line across the lower half of the Sun in this image, from 10 February 2015, shows a filament of solar material hovering above the Sun's surface. Credit: NASA
Source: Space Weather

In 1964, the late solar researcher Patrick McIntosh launched an ambitious effort to track sunspots—relatively cool, dark blotches on the Sun caused by disturbances in the star’s magnetic field. He traced sunspots and other solar surface features from daily photographs, creating a map of the full Sun approximately every 27 days. This led to important advances in the prediction of solar flares and helped to reveal the large-scale organization of the Sun’s magnetic field. Now scientists are working to preserve and digitize McIntosh’s project, a uniquely consistent record of solar activity over 45 years.

The Sun’s magnetic field is driven by the interior flow of hot plasma, or electrified gas, which creates a magnetic generator called a dynamo. McIntosh’s records showed that the location and number of sunspots and filaments—huge arcs of dense plasma that appear as dark lines on the Sun’s surface—are indicators of just how this dynamo works.

By carefully documenting the position and number of sunspots over time, for example, McIntosh’s record illustrated how the Sun’s entire magnetic field flips polarity every 11 years. The number of visible sunspots helps researchers predict this flip: When the Sun emits more X-ray and ultraviolet radiation, a period called the solar maximum, the number of sunspots peaks. When solar activity dwindles during the solar minimum, sunspots dwindle. McIntosh’s maps were unique for also tracking the position of filaments and other features that also change as the magnetic field evolves, drifting poleward or toward the Sun’s equator at different stages of the solar cycle.

Webb et al. scanned and digitally processed the hand-drawn maps that McIntosh created, known as synoptic maps, to create a free, public online archive. Ultimately, they plan to use the data to investigate long-term variations in the Sun’s activity and invite other researchers to use it as well. In recent years, the maps have provided important context for coronal mass ejections, the explosive bursts of solar wind plasma from the Sun that create the northern and southern lights and can pose a threat to Earth’s communication systems and power grid. (Space Weather,, 2017)

—Emily Underwood, Freelance Writer


Underwood, E. (2018), Preserving a 45-year record of sunspots, Eos, 99, Published on 17 January 2018.

Text © 2018. The authors. CC BY-NC-ND 3.0
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