Clouds on the Sun?

Vacuum Tower Telescope and ChroTEL                                

The Sun is far from being a boring and homogenous star. It hosts many interesting features, from small bright points to large-scale flare events, as reported the weeks before. Within solar physics, a particular topic are solar filaments or prominences. Both terms refer to the same phenomena, but receive different names depending on where they are observed on the Sun. On the solar disk, they are called filaments, while above the limb, they are called prominences. They are best seen using an H-alpha filter, even with amateur telescopes, and resemble dark clouds which lie in the chromosphere and corona (see image).

However, they are not like clouds on Earth! Filaments are made out of thin plasma threads located inside of large elongated structures. The structure itself is confined due to the magnetic field lines. Filaments are found in the upper layers of the atmosphere, between 2.000 and 10.000 km above the solar surface, have lifetimes of few days to several weeks, and their formation process is still not well understood. Since filaments are rooted in the photosphere, but their main body appears much higher in the atmosphere, they present a coupled system across several heights. Therefore, the EST multi-wavelength capabilities will offer a unique opportunity to better study filaments and shed light on the nature of these intriguing phenomena.

The image was taken with the full-disk Chromospheric Telescope (ChroTel, Tenerife) using an H-alpha filter on 2011 November 15. The lower part shows the same filament observed with a high-resolution telescope (VTT, Tenerife).

Image credit: C. Kuckein (AIP), M. Verma (AIP) and C. Denker (AIP), 2016, A&A, 589, A84