Solar Astrophysics
Our Sun, the star closest to Earth, offers us the opportunity to make detailed observations of the exterior and interior of a typical star in its mid-life phase. In addition, the Sun offers us a natural laboratory for the study of plasmas (high-temperature gases in which atoms have been stripped of their electrons) that are influenced by magnetic fields. From the details of the Sun's behavior, we can address questions about key processes within stars. How do they generate energy through nuclear fusion at their centers? How does that energy pass through hundreds of thousands of kilometers of surrounding layers of gas? How does that energy, released in the form of highly energetic particles and ultraviolet and infrared light waves, affect Earth and the Sun's other planets?
Careful study of the Sun's output of energy as different types of radiation will improve our knowledge of these processes. Better ground-based solar telescopes can reveal conditions on the Sun's surface at scales of distance as small as 70 kilometers - an important scale because the Sun's atmospheric pressure and temperature change noticeably over distances this small. Other solar phenomena, including the temporary cool and dark regions called sunspots, and the violent outbursts visible at and above the Sun's surface, have their origin below the visible layers of the Sun. With specialized instruments, we can deduce the conditions that exist below the surface layers and determine how these transient events arise and develop.
Our Sun continues to pose some difficult questions. How can the solar surface, with temperatures of only about 10,000 degrees Fahrenheit, produce the much hotter chromosphere above it and, above the chromosphere, the still hotter solar corona, where the temperature rises to a million degrees or more? How do the boiling motions in the outer layers of the Sun concentrate magnetic energy? What governs the sudden release of this energy as huge coronal mass ejections and solar flares? These outbursts eject huge numbers of electrons, protons, and other charged atomic nuclei, which disrupt the patterns of Earth's magnetic field when they reach us a few days later. Understanding the details of the Sun's behavior has important applications for both short-and long-term weather forecasting. In addition, solar outbursts disrupt radio, television, radar, and power transmission and create a danger for astronauts; changes in the Sun's energy output, even at a modest level, produce long-term, still poorly understood climate changes on Earth. To the extent that we can better understand how the Sun and its outbursts work, we can take steps to better protect ourselves and our planetary environment.
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