The Sun is just there, without us thinking much more about it. But because it affects us so much, it is essential that we learn more about it. As strange as it sounds, there is a lot we do not know about this star that keeps us alive. Issues involved in studies of the Sun today range from how the first stars were created, to how solar winds can knock out electrical systems on Earth, such as data and air traffic.

Grant for studying the chromosphere
Like Earth, the Sun has several atmospheric layers, and the lowest layer, the photosphere, corresponds to the visible solar surface. The upper atmosphere is divided into two, the chromosphere and corona which are located further out.


Sunspots Photo Göran Scharmer


Earlier this month, Göran Scharmer, professor at the Department of Astronomy at Stockholm University and the Royal Academy of Sciences, received SEK 26.3 million from the Knut and Alice Wallenberg Foundation. The grant is for installing a custom-made filter system on the Swedish Solar Telescope (SST) on the Canary Island of La Palma in order to study heating and gas movements in the chromosphere. The density of the chromosphere is so low that it is not visible in normal light, but it is hotter than the lower layers and radiates a lot of energy. Using the filter, researchers will try to find out where the energy comes from.

“Our starting point is the best possible. We have a world-leading telescope that can capture smaller details on the Sun than other telescopes. The grant from the Knut and Alice Wallenberg Foundation enables us to equip the telescope with a filter system by which we can measure the temperature and the speed of gas in the chromosphere with unprecedented detail. In addition, the grant covers the costs for researchers, graduate students and technicians who will implement the project. Grants are of utmost importance for our future research in solar physics,” says Göran Scharmer.

Another exciting aspect that the researchers will investigate is how the chromosphere interacts with the much hotter corona surrounding the chromosphere. The corona is the outermost layer of the Sun’s atmosphere, with a temperature of over a million degrees Celsius, and it extends millions of kilometers into space. The corona is clearly visible from Earth only at a total solar eclipse, i.e. when the Moon completely covers the Sun and the corona radiates outside the shadow of totality. The corona cannot be studied particularly well with ground-based telescopes because its radiation of energy consists of an ultraviolet light which is absorbed by the atmosphere. For such observations, a space telescope, IRIS, is used, and coordinated observations are made with the Swedish Solar Telescope.

Text: Per Nordström