GREGOR is the largest European Solar Telescope and recent enhancements in optics have allowed us to observe the Sun in extremely high resolution. The images show two snapshots, taken in August 2018 and the size of the Earth for comparison.

The controller of the Fabry-Perot Etalon for the Visible Tunable Filter instrument (VTF) has reached the demanding requirements for the controller precision and speed. The distance of the 20 kg Etalon plates can now be adjusted within a few milliseconds to the precision of a medium size atom. This is an important milestone towards the realization of the VTF. The multi-level controller was developed at KIS and has been verified on the basis of a full-size model of the Etalon.

The Leibniz-Institute for Solar Physics (KIS) has released a beta version of the new data archive for the GREGOR Infrared Spectrograph (GRIS, Collados et al. 2012, see below). All GRIS data prior to 2018 are in open access and available here: sdc.leibniz-kis.de

The database contains more than 650 data sets recorded in the years between 2014 and 2017. Most of them are single raster scans recorded in spectropolarimetric mode in the 1.08µm and 1.56µm wavelength bands. Some of them are measurements in spectroscopic mode, time sequences capturing the evolution of solar features, sit and stare measurements or observation in other wavelength bands such as 2.2µm.

Currently, the user can access the archive via a web interface. Best performance is achieved using ‘Chrome’ Browser. The initial web page provides the possibility to query by various parameters such as date, wavelength, heliocentric angle, etc. The results are displayed as a list with some information and preview images. For each...

Internal gravity waves (IGWs) are buoyancy-driven waves common in the Earth’s atmosphere and oceans. IGWs have also been observed in the Sun’s atmosphere and are thought to play an important role in the overall dynamics of the solar atmosphere.

Solar spectral lines have different shapes, strengths, asymmetries and wavelength shifts. These differences depend on the chemical element, and on the corresponding excitation state.

At the Vacuum-Tower-Telescope on Tenerife we conducted systematic observations of a number of spectral lines in the visible part of the solar spectrum, and measured the center-to-limb variation of the parameters mentioned above. To allow for a comparison of all the measurements, we used the Laser Absolute Reference Spektrograph.

The outer envelope of the Sun is highly magnetic and vigorously turbulent. We have employed concepts of phenomenological thermodynamics and information-theoretic entropy and discovered new, consistent patterns in evolution of solar magnetic fields.

The European Union's Programme on Research and Innovation, H2020, is funding the SOLARNET project for 4 years under the grant agreement number 824135. The project started on January 1st, 2019, and will end on December 31st, 2022.

The „Visible Tunable Filter“(VTF) is a spectro-polarimeter that is presently being built at KIS, and will be installed at the US-American Daniel K. Inouye Solar Telescope as a focal plane instrument in about two years from now. The VTF will be used to measure magnetic fields with high spatial resolution on the Sun. To this end, the VTF measures precisely the state and the degree of polarization of the incoming solar light.

The boundary between the umbra and the penumbra of sunspots has untill recently been defined by an intensity value only. Using Hinode satellite data, Jurcak et. al 2018 found an empirical law of the magnetic nature of the umbra-penumbra boundary in stable sunspots: an invariant vertical component of the magnetic field.

In the dark umbra of a sunspot, the convective motion is largely suppressed by the strong magnetic field. In the past, numerous studies have reported on negligible convective flows (e.g., Beckers 1977). Based on this, the umbra typically served as the zero-velocity reference for the calculation of Doppler velocities of an active region.