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Vector-Point Diagrams (left panels) and proper-motion component vectors (right panels) for identified member stars in the open clusters Ruprecht 1 and Ruprecht 171. These two previously little-studied open clusters, both at a distance of approximately 1.5 kpc, have been characterized and studied in some detail in the related paper by Çakmak and collaborators, published in this issue e240054.

First-light spectra of the Sun as a star taken by SDI-POL, the Solar Disk Integration POLarimeter feeding the PEPSI night-time spectrograph at the LBT. The top panel shows the full wavelength range (383 - 907 nm) covered by SDI-POL. The color of the Stokes I spectra indicates the individual cross dispersers; dark blue (=CD 1) to dark red (=CD 6). The line at the bottom represents the normalized Stokes V Q & U signal on the same intensity scale as Stokes I. The bottom panel is a zoom into the spectral region around the sodium D lines. The top spectrum is again Stokes I (plotted are dots per CCD pixel connected by a line), the bottom spectra are Stokes V Q U shifted by -0.10 in intensity and expanded by a factor 200 in scale with respect to Stokes I. The I Q U spectrum was taken on UT May 20, 2022, the V-spectrum on UT June 22, 2023. The first-light application detects a clear Stokes V/I profile indicative of a tiny but significant solar disk-averaged line-of-sight net magnetic field of +0.37±0.02 Gauß on Oct. 13, 2023, as reported in the article by Strassmeier et al., this issue, e240033.

This study discusses historical records of Korea that mention “stars” possibly related to astronomical transient events. We selected 19 such records and scrutinized them by cross-checking with records of other countries to identify those events. Ten events were identified as comets based on their described motions and tails. We further confirmed this by comparing them with records from other countries. Five events were classified as meteors based on descriptions of their movements, sizes, and shapes. We speculate that two recordings about “big stars” (大星) are typographical errors for “Mars” (火星), as the descriptions of these big stars seem to be consistent with the properties of the latter. This leaves two unidentified events, and we search lists of astronomical transients for their counterparts. Our work emphasizes the uncertainties and challenges caused by the limited information in the historical records while exploring the usefulness of historical records to enhance the understanding of astrophysical transient events.

Astrophysical accretion discs that carry a significant mass compared with their central object are subject to the effect of self-gravity. In the context of circumstellar discs, this can, for instance, cause fragmentation of the disc gas, and—under suitable conditions—lead to the direct formation of gas-giant planets. If one wants to study these phenomena, the disc's gravitational potential needs to be obtained by solving the Poisson equation. This requires to specify suitable boundary conditions. In the case of a spherical-polar computational mesh, a standard multipole expansion for obtaining boundary values is not practicable. We hence compare two alternative methods for overcoming this limitation. The first method is based on a known Green's function expansion (termed “CCGF”) of the potential, while the second (termed “James' method”) uses a surface screening mass approach with a suitable discrete Green's function. We demonstrate second-order convergence for both methods and test the weak scaling behavior when using thousands of computational cores. Overall, James' method is found superior owing to its favorable algorithmic complexity of $��\sim �O�\left(n^3\right)�$ compared with the $��\sim �O�\left(n^4\right)�$ scaling of the CCGF method.

The Nebra Disk is one of the earliest astronomical manifestations of humanity in Central Europe. We interpret the striking sevenfold stellar group shown on the disk as a celestial conjunction of the five naked-eye visible planets together with Pollux and Castor in the constellation Gemini (happening in 2210BC) and the dominating large, filled circle as a bright supernova, probably corresponding to the remnant 3C58 in Cassiopeia. We believe that a close coincidence of these two extremely rare celestial events, that does never happen more than once in a human lifetime, could have impressed people of that epoch in a way that it was conveyed orally over several generations, until some Bronze Age artist created the Nebra Disk. If this interpretation is correct, it could offer a rather exact dating of a supernova explosion observed about 4200 years ago, more precise than any other dating methods for past supernova events, possibly leading to significant new insights into the underlying physics of supernovae.