National Astronomical Observatory of Japan | 2020 Oct 12
New research shows that sunspots and other active regions can change the overall solar emissions. The sunspots cause some emissions to dim and others to brighten; the timing of the changes also varies between different types of emissions. This knowledge will help astronomers characterize the conditions of stars, which has important implications for finding exoplanets around those stars.
An international research team led by Shin Toriumi at the Japan Aerospace Exploration Agency added up the different types of emissions observed by a fleet of satellites including Hinode and the Solar Dynamics Observatory to see what the Sun would look like if observed from far away as a single dot of light like other stars.
The team investigated how features like sunspots change the overall picture. They found that when a sunspot is near the middle of the side of the Sun facing us, it causes the total amount of visible light to dim. In contrast, when the sunspots are near the edge of the Sun the total visible light brightens because at that viewing angle bright structures known as faculae surrounding the sunspots are more visible than the dark centers.
In addition, X-rays which are produced in the corona above the solar surface grow brighter when a sunspot is visible. The coronal loops extending above the sunspots are magnetically heated, so this brightening appears before the sunspot itself rotates into view and persists even after the sunspot has rotated out of view. ...
Studying the Sun as a Distant Star: Contributions to
Investigations of Massive Flares and Exoplanet Habitability
Institute of Space and Astronautical Science | Japan Aerospace Exploration Agency | 2020 Oct 12
Sun-as-a-Star Spectral Irradiance Observations of Transiting Active Regions ~ S. Toriumi et al