In France, the Sun is actively observed at Meudon, at the Pic du Midi and in Nançay in the radio spectrum. In order to take advantage of the good observational conditions at the Izana site (2400m altitude) on the island of Tenerife (one of the Canarian Islands), the construction of the solar telescope THEMIS (Telescope Heliographic for the Study of Magnetism and Instabilities of the Solar atmosphere) was undertaken by France, Italy and Spain to measure the polarization of the spectrum solar lines with high spatial, spectral and temporal resolution. The telescope was put into service in 1999.
The Sun is a very special star: it is the only star close to Earth. To observe it, it is necessary to have specific observatories and telescopes to solve problems that we do not encounter by observing the other stars. The enemy of solar observation is the atmospheric turbulence and the heating of the air and of the telescope. To avoid this, the THEMIS telescope (90cm in diameter) is placed under vacuum. The secondary mirror and the receivers are further cooled.