The Universe and Galaxies: Solar Research

Discovery Space: Solar Research

Many phenomena related to the sun can be observed and studied from Earth. A more detailed investigation of developing solar magnetic fields and flares is, however, made possible by the use of space probes and satellites.

Ancient cultures observed and studied the position of the sun throughout the year, recording important or unusual events such as solar eclipses. But the invention of the telescope around 1600 was the break- through, finally allowing systematic observation of the sun’s surface.

However, specialized equipment must be used for this, as observations of the sun may lead to serious eye damage or even blindness. One of the major advances in solar research in the 19th century was the discovery of dark lines in the solar spectrum of light. In 1814 Joseph von Fraunhofer began to systematically study these lines, which were later named after him.

The composition of the outer gas layers of the sun can be derived from them. The sun was first recognized as a source of energy during the first half of the 20th century, when hydrogen fusion was discovered. Solar radio waves and x-rays were also discovered, and the first solar vibrations were measured during the second half of the century.

This provided much information about the inner structure of the sun. Giant underground detectors were built to measure the level of neutrinos emitted by the sun. Neutrinos, which have no electric charge and can easily pass through solid matter, are generated during solar energy production.

Satellites and space probes

Several satellites observe the sun from orbit. They are especially useful for studying the parts of solar radiation that are blocked by the Earth’s atmosphere, such as ultraviolet radiation and x-rays. Due to the high temperatures and intensive radiation, it is technically challenging to bring space probes close to the sun. In the 1970s, Helios 1 and 2 were sent into elliptical orbits around it, and were able to reach less than one-third of the Earth’s distance in proximity.

The space probe Ulysses has been orbiting around the sun and across its solar poles since 1990. This allows a unique view of the solar magnetic field from the “top” and “bottom” perspectives. The Solar and Heliospheric Observatory (SOHO) has been orbiting along the Earth-Sun line since 1995. The space probe is orbiting the First Lagrangian Point (L1), while the Earth simultaneously orbits the sun. A second satellite called TRACE was sent for support in 1998.

Together, they track the development of magnetic fields, plasma structures, and mass ejections of the sun. They are a major contributing factor in the prediction of solar flares. Two STEREO space probes have been in orbit around the sun since 2006. One of them is traveling ahead of the Earth, while the other one is traveling behind. This allows for three-dimensional measuring of processes taking place within the sun and solar wind.


A spectrograph splits the light according to its wavelength, similarly to the way a glass prism does, but in much more detail. Many parts of sun spectra recorded in this way show dark lines. These are the result of various gases from the photosphere absorbing light of certain wavelengths.

This allows analysis of the sun’s chemical com- position. The magnetic field of the sun can also be measured using the spectrograph method because it splits the lines. Even the light of other stars can be analyzed.


THE SUNS ENERGY SOURCE was not known until the 20th century. Previously it was thought that the sun might consist of glowing coal. A further idea was that the sun might have drawn energy under compression from its own gravity.