Solar flares were discovered by Carrington (1859) and Hodgson (1859) through their white-light emissions. Although the emission mechanism of white-light flares is still not understood today, we now know that such radiation is produced at the footpoints of flaring magnetic loops. Compared to the pre-flare variability of the Sun in the optical range, white light flares only locally enhance the emission. White light flare sources therefore are clearest seen in large flares but could be possibly present in all flares. Joint observations in the optical, X-ray, and gamma ray range reveal that the white light flare emission process is somehow linked to the energy deposition of flare-accelerated electrons and ions as they interact and heat the lower layers of the solar atmosphere. In this talk, I will give first an introduction to white light solar flares and then show new results obtained by the hard X-ray telescope STIX onboard Solar Orbiter and AIA/HMI.
A new era of solar physics commences with observations of the quiet Sun using the 4-metre Daniel K. Inouye Solar Telescope/Visible Spectropolarimeter (DKIST/ViSP). We present full-Stokes observations taken during DKIST’s cycle 1, in the Fe I 630.1/630.2 nm lines, allowing us to examine small-scale magnetism in the photosphere. We use the Stokes Inversion based on Response functions (SIR) code to invert the Fe I line pair. We reveal the existence of a serpentine magnetic element for the first time. A statistical analysis is undertaken, comparing inversions of DKIST data with Hinode data. A novel machine learning technique is used to characterise and contrast the shapes of circular polarisation signals found in the ground-based and space-based data, and synthetic observations produced from MANCHA simulations are used to aid our understanding of the differences between datasets.
After recalling the textbook narrative of why the quantum-mechanical approach to radiating atoms is not satisfactory (at the end of which the reader is usually referred to quantum field theory for a more satisfactory approach), we present a novel quantum-mechanical approach to the problem that succeeds in some crucial aspects where the traditional approach fails, and which holds the promise to be developed into a mathematically simpler alternative to so-called non-relativistic QED (a.k.a. the standard model of everyday matter and its radiation). Important ingredients in this novel formulation are two of Max Born's key insights into the physical meaning of Schroedinger's Psi function, combined with some related insights of de Broglie, and subsequent ones by Pauli, and by Dirac, all from the 1920s.