Solar observatory Einstein Tower -- Data release of the digitized solar full-disk photographic plate archive

TL;DR

This paper presents a digitized archive of solar full-disk photographic images from the Einstein Tower (1943-1991), with calibrated, high-resolution data made publicly available for research and educational purposes.

Contribution

It provides a large, calibrated, and accessible digital archive of historical solar observations, digitized by students, enhancing data availability for solar research.

Findings

Over 3500 images digitized and calibrated

Images cover Solar Cycles 18-22 (1943-1991)

Data freely accessible in FITS format

Abstract

We present solar full-disk observations, which were recorded at the Einstein Tower during the years 1943 - 1991 (Solar Cycles 18 - 22). High-school students from Potsdam and Berlin digitized more than 3500 full-disk images during two- to three-week internships at AIP. The digital images cover a 15 cm $\times$ 15 cm region on photographic plates, which were scanned at a resolution of 7086 $\times$ 7086 pixels. The raw data are monochromatic 8-bit images in the Tagged Image File Format (TIFF). These images were calibrated and saved with improved photometric precision as 16-bit images with 2048 $\times$ 2048 pixels in the Flexible Image Transport System (FITS) format, which contains extensive headers describing the full-disk images and the observations. The various calibration steps include, for example, accurate measurements of the solar radius, determination of the limb-darkening function, and establishing an accurate coordinate system. The contrast-enhanced and limb-darkening corrected images as well as the raw data are freely available to researchers and the general public in publicly accessible repository. The data are published as a special data release of the Archives of Photographic PLates for Astronomical USE (APPLAUSE) project.