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Solar & Heliospheric Physics

The Sun is the best laboratory we have for studying stars and how they influence the planets orbiting them. Space- and ground-based observatories monitor day-to-day fluctuations in the Sun’s light, atmosphere, and magnetic field. In addition, we have roughly four centuries of historical sunspot data, tracing the history of magnetic activity on the Sun. These observations provide essential information about the physical processes on the Sun, which reveal its history and future. In addition, they reveal the ways the Sun influences Earth and other Solar System bodies, as well as giving us insight into the behavior of other stars throughout the cosmos.

The Mysterious Star We Know Best

The Sun is only 150 million kilometers (93 million miles) away from Earth, which is a tiny distance in cosmic terms. That relative closeness lets us observe the Sun to a level of precision we can’t achieve for any other star.

The field of solar and heliospheric physics enfolds the processes that make the Sun shine, produce its magnetic field, shape its atmosphere, and send particles across the Solar System, which is called the solar wind. Solar physics involves understanding the internal processes of the Sun, which produce its magnetic field, and the dynamics of its atmosphere. The range of influence for the solar wind is called the heliosphere, which extends far past the orbit of Pluto.

  • While we can’t see inside the Sun directly, solar physicists can still infer what’s going on using the sound waves traveling through the interior. These waves produce variations on the Sun’s surface, much like earthquakes. Helioseismology is the study of these waves and what they tell us about the Sun’s interior. [ link to “stellar structure” page ]

  • The Sun generates a powerful magnetic field, which in turn accelerates electrically charged particles — electrons and ions — in its atmosphere to high speeds. The magnetic field’s intensity cycles over a period of eleven years. That produces fluctuating numbers of sunspots, which are dark places on the Sun where the field is particularly intense. At periods of higher activity, the Sun produces more of the outbursts known as coronal mass ejections, which can disrupt communications and power grids on Earth. For that reason, solar physicists study the magnetic cycle to try to predict these events.

  • Perhaps the biggest mystery about the Sun is the temperature of its atmosphere. While the surface is around 5500º C (9900º F), the solar atmosphere rises to millions of degrees for reasons we don’t fully understand. The outermost layer of the atmosphere, the Sun’s corona, is one of the Solar System’s most extreme environments, with high temperatures stripping electrons from atoms and magnetic fields whipping particles to high speeds.

  • The hot atmosphere is too dynamic for the Sun’s gravity to hold in entirely. As a result, the Sun is always shedding charged particles — mostly electrons and protons — which constitute the solar wind. Those particles flow into the Solar System, where they interact with the magnetic fields of planets like Earth, creating auroras. The solar wind also pummels comets, producing their characteristic tails, and bombards asteroids, shifting their orbits and rotation rates. The range of influence of the solar wind extends far beyond the orbit of Pluto, and defines the heliosphere.

 

This artistic depiction of NASA's Parker Solar Probe shows the spacecraft on its approach to the Sun. The probe passes through the outermost layers of the solar atmosphere, collecting particles and taking measurements to understand solar weather.

Credit: NASA