A New Astronomical Plate Digitizer at Shanghai Astronomical Observatory

Abstract The advancement of astronomy relies fundamentally on observational data. Between 1850 and 2000, astronomical observatories worldwide produced vast collections of photographic plates that remain invaluable for studying long-term celestial phenomena. However, these plates now face irreversible degradation, threatening their scientific value. Recognizing this urgency, Shanghai Astronomical Observatory (SHAO) developed a new plate digitizer incorporating a reliable air-bearing motion platform, a sophisticated imaging system, a stable illumination system, a design-optimized camera rotation mechanism and a custom-automated plate chamber. The system ensures the stability through active temperature and humidity control and vibration damping, while systematic error analysis and calibration further enhance operational performance. Tests show that the digitizing repeatability in positioning is better than 0.1 μ m, repeatability in photometry is better than 0.01 mag, and the overall digitizing accuracy is about 0.3 μ m in positioning and 0.02 mag in photometry. Currently, SHAO is collaborating internationally to digitize the endangered archives, providing support for the protection of scientific data heritage and research in long-term time-domain astronomy.