Picture of the Month

0.000 000 000 5 metre (= 0.5 nanometres = 0.5 nm), this tiny distance is how the two plates made of quartz glass fit together. Over an extension of 25 cm in diameter, the distance between the two plates varies by less than the distance of two neighbouring atoms in a silicon crystal. These two glass plates make up the Fabry-Perot interferometer of the VTF.

Read more

The VTF (Visbile Tuneable Filter) is a two-dimensional high-resolution spectropolarimeter and is currently developed at the Kiepenheuer Institute. As one of the state-of-the-art scientific instruments at the future 4-m-class telescope DKIST on Hawaii it will play a major role in the next decade of solar observations.

The setup of the VTF consists of several Fabry-Pérot interferometers (FPI), a wavelength-dependend narrow pre-filter and a polarization modulator. Due to the requested accuracy of the physical measurements, an investigation of the instrumental impacts on the physical data acquisition was required in advance. Based on the inquired simulations, the requirements for manufacturing were inferred and strategies for the data calibration developed.

Read more

LARS, the Laser Absolute Reference Spectrograph of the Kiepenheuer-Institute is a scientific instrument for the ultramodern observation of the Sun at the Vacuum Tower Telescope (VTT) at the Observatorio del Teide on Tenerife. LARS enables the measurement of the solar spectrum of a selected field-of-view with the high-resolution Echelle-spectrograph of the VTT. Additionally, the emission spectrum of the newly installed Laser Frequency Comb is superimposed with the solar spectrum. Since each emission peak of the comb spectrum represents one well-defined frequency, the solar spectrum can be calibrated on an absolute wavelength scale. Figuratively, the comb serves as a ruler for the spectral lines. The accuracy is of the order of m/s or below and is therefore a multiple better than former devices. The successful upgrade of the Laser Frequency Comb in May 2016 enables the continuous operation of this worldwide unique spectroscopic observation of the Sun.

Read more

In a recently published work, KIS researchers and colleagues from MPS Göttingen present a new spherically geometric method for modelling the effect of flows on travel times of sound waves in the solar interior. This development is necessary for advancing our understanding of large-scale flows in the deep solar interior and thereby to gain insights on the origin of solar activity.

Read more

The exact configuration of this magnetic field is important to understand the different features seen in sunspots. In the umbra, the dark center, the field is oriented perpendicular to the surface, while it is more horizontal in the penumbra, i.e. the surrounding region with narrow radially oriented filaments. Parts of the magnetic field continues into higher regions, while some of it reverses its polarity and returns back into the Sun. In the left panel of the figure we show observation with the Hinode satellite of the penumbra of a sunspot. Regions where the field returns below the surface are colored in red and blue. In the red regions, the polarity reversal is just above the surface, while it occurs in higher layers in the blue regions. The right panel show measurements with the new GREGOR Infrared Spectrograph (GRIS) at the Observatorio del Teide on Tenerife. The amount of red and blue regions in this observation is significantly less than the one found in Hinode data. The reason for this difference is subject of current studies at the KIS.

 

References:...

Read more

On May 9th, Mercury will transit in front of the solar disk. To make this happen Earth has to be in a certain position in its orbit: The intersection points of the two planet’s orbits. They are called nodes. This happens twice a year: Around 8th of May and around 10th of November. In addition Mercury has to be in the corresponding position. This only happens every couple of years. In the 21st century there will be 14 Mercury transits: 5 in May and 9 in November. The last time it was in November 2006 and the next time it will happen in November 2019. Mercury’s angular diameter is too small to be observed by naked eye but the Kiepenheuer-Institute’s solar telescopes on Tenerife will observe the transit. It starts on 13:12 CEST and Mercury leaves the Sun at 20:40 CEST. During that time two kinds of observations will be performed: Mercury will be used as a target to determine optical properties of the telescope. Furthermore there will be measurements of the particle density of sodium close to Mercury’s surface: Various processes including the solar radiation releases a small amount of atoms (e.g. sodium) from the planet forming an extremely faint gas envelope (exosphere) and a tail....

Read more

Today solar science is a diverse and rapidly evolving discipline. But the roots of solar science can be traced back to ancient times and beyond. Especially the observation of dark sunspots has a long tradition. While the oldest plausible record dates back to Chinese astronomers (800 BC), the first sunspot drawing was made in 1128 by the monk John of Worcester observing large sunspot formations visible to the naked eye.

At the beginning of the 17th century, several astronomical milestones were set to modernize the human understanding of the Sun. In 1609, Johannes Kepler expanded the heliocentric system to include elliptical orbits of the planets around the Sun. In the same year, the invention of the telescope became the starting shot in a new era of solar and stellar observations.

Read more

GREGOR is a modern 1.5m solar telescope. It is also highly suitable for observing the planets of our solar system. Recently, a new instrument was built to study certain properties of the planetary atmospheres. It allows for high-precision polarisation measurements of the light reflected by the planets. In order to reach a high spacial resolution, the instrument uses the adaptive-optics system (AO) of the telescope. For this purposes, the AO normally used for solar observations had to be extended with an additional wave-front sensor for observing the much fainter objects at night.

In November 2015, polarisation measurements of Uranus in different spectral ranges were recorded. The picture shows three measurements at 450, 550 and 650nm. The first row (I) shows the normal-intensity image of the planet. In the next two rows (Q/I and U/I), images of the linear polarized part of the light are shown. The black and white pattern indicates that part of the light is polarised parallel to the...

Read more

German-Norwegian team of scientists observes heart-shaped sunspot with GREGOR, the largest European solar telescope.

Read more

The magnetic field of a sunspot guides magnetohydrodynamic waves toward higher atmospheric layers. In the upper photosphere and lower chromosphere, wave modes with periods longer than the acoustic cut-off period become evanescent. The cut-off period essentially changes due to the atmospheric properties, e.g., increases for larger zenith inclinations of the magnetic field. These relations were now employed to develop a novel technique of reconstructing the magnetic field inclination on the basis of the dominating wave periods in the sunspot chromosphere and upper photosphere. 

On 2013 August 21st, an isolated, circular sunspot (NOAA11823) for 58min was observed in a purely spectroscopic multi-wavelength mode with the Interferometric Bidimensional Spectro-polarimeter (IBIS) at the Dunn Solar Telescope. By means of a wavelet power analysis, the dominating wave periods were retrieved to reconstruct the zenith inclinations in the chromosphere and upper photosphere.

The results shown in...

Read more