The Principal Investigator (PI) and her collaborators will take multi-spectral observations during several upcoming solar eclipses in order to map the ion abundance, electron temperature, and direction of the coronal magnetic field in the inner corona. The team plans to study the distribution of neutral hydrogen and helium in the solar corona, as well as to investigate the properties of dust grains in the near-Sun environment. Data will be obtained in the spectral lines of ionized iron, sulfur, and silicon, as well as in neutral helium and hydrogen. Coupled with laboratory experiments, these observations will enable detection of fluorescence signatures of interplanetary dust grains present in the solar corona.

This project will exploit the complementary diagnostic techniques of resonant scattering and polarization to follow the evolution of ions and neutrals in the solar corona. Heavy ions and traces of lighter neutral atoms (such as hydrogen and helium) in the inner corona serve as local probes of the physical processes that heat the solar atmosphere to over one million degrees and accelerate the solar wind. While ions are tied to coronal magnetic fields, neutrals reflect the fate of cooler material from solar as well as interstellar origin. As ions and neutrals expand away from the Sun, they interact and evolve under the influence of the local magnetic field, the local electron temperature, and through collisions. This research will enhance our understanding of these phenomena.

In previous eclipse expeditions, members of the research team have been successful in raising public awareness of scientific research in general and of solar physics in particular. Their prior efforts have proved to be engaging for the imagination and intellect of younger students specifically. The research team represents a fruitful collaboration involving small and large universities led by a senior female scientist. The eclipse expeditions will involve graduate students, postdoctoral fellows, and a K-12 teacher, with an emphasis on education.

Project Report

Total solar eclipses remain one of Nature's most beautiful displays. These events occur when the Moon totally blocks the bright disk of the Sun and casts a shadow on Earth. It is at that moment that one can see the outer atmosphere of the Sun, called the solar corona, or crown. In fact, the discovery of the solar corona was made possible by this particular astronomical alignment of the Sun, the Moon and Earth, that occurs almost once every year to year and a half. The shadow band on Earth is about 100 miles wide, and is cast over different parts of the world at each eclipse, depending on this alignment. In 2010, the path of totality traversed a few atolls (very tiny islands) in French Polynesia, as well as Easter Island, and lasted for almost 5 minutes. Despite the proliferation of satellites observing the Sun from space, in different parts of the solar spectrum, observations carried out during total solar eclipses remain scientifically invaluable. The simple reason being that the field of view of the solar corona that can be imaged during a total solar eclipse far surpasses what can be achieved from space, starting from the visible surface of the Sun out to several solar radii. The Solar Wind Sherpas, as my group is called, consists of colleagues from different institutions across the United States and from Europe. We have been imaging the solar corona for several decades. The improvement of technology and image processing techniques have led us to new discoveries regarding the physical properties of the solar corona. Our knowledge of all astronomical objects goes back to the analysis of the different components of light originating from the object and detected by our cameras and telescopes. Each color of light corresponds to a different element. Iron, Fe, produces the largest number of colors (which we also refer to as spectral lines) in the solar corona.The presence of different ionized states of Fe led to the discovery in the early 1900's that the solar corona had a temperature exceeding one million degrees, at least 100 times fold the 5800 degrees surface temperature of the Sun. The big mystery that persists until present is what causes this outer atmosphere to be so hot. The first image shows the solar corona in white light, as the naked eye would see it. The white light emission is produced by the free electrons streaming away from the Sun and reflecting the light from the solar disk in all directions.This image has been processed to reveal the intricate details of the structures in the solar corona. These structures delineate the intricate paths that the magnetic field takes as it emerges from the solar surface. As charged particles follow the magnetic field paths, or lines, they provide a very nice probe of how these, otherwise invisible, field lines are emerging from the solar surface and expanding into interplanetary space, eventually interacting with the magnetic fields of planets, and most importantly for us, with the Earth's magnetic field.These intricate details are a reflection of the origin of the field lines from different parts of the solar surface, as well as a snapshot of the disturbances propagating through the corona. Observing the Sun in different colors, such as shown in the second and third images, enables us to explore the behavior of different elemental species present in the solar atmosphere, such as iron (Fe), nickel (Ni), .... What we found is that the corona 'appears' very different depending on the color and the element in which it is observed. All features in the corona that look like arches are the hottest, at two million degrees (see green color), and what is streaming away from the Sun is cooler at one million degrees (red). This two-temperature distribution is evident in all the eclipse observations, and seems to be independent of the magnetic activity cycle of the Sun with time. We also discovered that in some regions of the solar corona, different charge states can become trapped and produce an enhanced emission. Total solar eclipses provide unique opportunities for scientific investigations. But they also provide fascinating opportunities for the public if properly prepared for the occasion. The challenge with the preparation is for people to protect their eyes during the partial phases of totality as the Moon seems to traverse the disk of the Sun, until totality, when the solar disk is totally covered by the Moon and the corona is fully exposed. At that moment, no protective measures for the eyes are necessary. The fourth image shows children and their parents in Tatakoto getting ready for the eclipse. The path of the total solar eclipse of 21 August 2017 will traverse the US continent from northwest to southeast, and provides a not-to-be missed opportunity.

National Science Foundation (NSF)
Division of Atmospheric and Geospace Sciences (AGS)
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Paul Bellaire
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University of Hawaii
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