A host of space telescopes and satellites have been launched to study the Sun in recent years. But there are also plenty of observatories back on Earth whose focus is observing our home star. 

One of the major centres for solar studies is on the holiday island of Tenerife, high on the Moon-like landscape of the plateau surrounding Mount Teide called Las Cañadas.

I remember this already being an important observatory way back in the early Seventies when I was a young site-tester on the plateau checking sky conditions for another planned observatory that ended up being built on the neighbouring island of La Palma.

Now a new German solar telescope has been added to the mushrooming number of solar instruments at the site, called the Spanish Observatorio del Teide of the Instituto de Astrofísica de Canarias at Izaña. Called GREGOR, it is the largest solar telescope in Europe and the third biggest in the world.

This telescope, which will be inaugurated on May 21, is unusual because it will also be used at night to observe bright stars and compare their cycle of activity changes with the Sun.

GREGOR has a mirror 1.5 metres across (5ft) and will observe the Sun’s visible surface, called the photosphere, and the lower region of its atmosphere called the chromosphere, in the visible and infrared regions of the spectrum. A range of instruments in neighbouring laboratory rooms will examine the light to study how these solar regions interact with the Sun’s magnetic field and movement of hot plasma.

Like many telescopes nowadays, a system of adaptive optics will compensate for atmospheric disturbances. Together with the large diameter this will allow observation of the Sun in great detail, down to features just 70km across, which the German team claim will be similar to what can be achieved in space.

Another unusual aspect of GREGOR is that it will operate in the open rather than a dome to allow the wind to cool the telescope’s structure and its mirrors. Its protective housing slides away to allow this.

The main mirror, or primary, is relatively lightweight and made from a material that does not change its shape under the heat of the brilliant Sun. It is also has a cooling mechanism added to the back of the primary to prevent it from heating up and producing image-distorting turbulence.

GREGOR, which will be open to use by astronomers from all over the world, was built by a German consortium led by the Kiepenheuer-Institut für Sonnenphysik in Freiburg with partners the Leibniz-Institut für Astrophysik Potsdam and the Max-Planck-Institut für Sonnensystemforschung in Katlenburg/Lindau.

Other contributions were made by the Instituto de Astrofísica de Canarias, the Institut für Astrophysik Göttingen, and the Astronomical Institute of the Academy of Sciences of the Czech Republic.