Heliophysics at total solar eclipses

Abstract

Observations during total solar eclipses have revealed many secrets about the solar corona, from its discovery in the 17th century to the measurement of its million-kelvin temperature in the 19th and 20th centuries, to details about its dynamics and its role in the solar-activity cycle in the 21st century. Today's heliophysicists benefit from continued instrumental and theoretical advances, but a solar eclipse still provides a unique occasion to study coronal science. In fact, the region of the corona best observed from the ground at total solar eclipses is not available for view from any space coronagraphs. In addition, eclipse views boast of much higher quality than those obtained with ground-based coronagraphs. On 21 August 2017, the first total solar eclipse visible solely from what is now United States territory since long before George Washington's presidency will occur. This event, which will cross coast-to-coast for the first time in 99 years, will provide an opportunity not only for massive expeditions with state-of-the-art ground-based equipment, but also for observations from aloft in aeroplanes and balloons. This set of eclipse observations will again complement space observations, this time near the minimum of the solar activity cycle. This review explores the past decade of solar eclipse studies, including advances in our understanding of the corona and its coronal mass ejections as well as terrestrial effects. We also discuss some additional bonus effects of eclipse observations, such as recreating the original verification of the general theory of relativity.

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Figure 1: Stereographic map of the 21 August 2017 eclipse.
Figure 2: The most recent total solar eclipse, photographed from Ternate, Indonesia, in 2016.
Figure 3: The 2013 total solar eclipse, observed from Gabon.

© 2013 JAY PASACHOFF, ALLEN DAVIS, VOJTECH RUSIN / © 2014 MILOSLAV DRUCKMULLER

Figure 4: The paths of total and annular solar eclipses between 2001 and 2025.

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Acknowledgements

I thank S. Koutchmy, Z. Qu, H. Kurokawa, I. Kim, T. Chandrasekhar and J. Singh for information about articles from their respective countries. My research on the 2017 eclipse is supported in large part by grants from the Solar Terrestrial Program of the Atmospheric and Geospace Sciences Division of the US National Science Foundation and from the Committee for Research and Exploration of the National Geographic Society.

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M. Pasachoff, J. Heliophysics at total solar eclipses. Nat Astron 1, 0190 (2017). https://doi.org/10.1038/s41550-017-0190

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