Blind Date: Using proper motions to determine the ages of historical images

TL;DR

This paper introduces 'Blind Date', a technique that estimates the date of historical astronomical images by using star proper motions, improving calibration accuracy without prior metadata, and achieving reliable dating within months to a decade.

Contribution

It presents a novel method for dating historical images using proper motions, eliminating the need for prior image metadata and enhancing astrometric calibration accuracy.

Findings

Successfully dated 85% of images within a decade

Achieved date estimates within months for many images

Performance depends on image quality and star signal-to-noise ratios

Abstract

Astrometric calibration is based on patterns of cataloged stars and therefore effectively assumes a particular epoch, which can be substantially incorrect for historical images. With the known proper motions of stars we can "run back the clock" to an approximation of the night sky in any given year, and in principle the year that best fits stellar patterns in any given image is an estimate of the year in which that image was taken. In this paper we use 47 scanned photographic images of M44 spanning years 1910-1975 to demonstrate this technique. We use only the pixel information in the images; we use no prior information or meta-data about image pointing, scale, orientation, or date. Blind Date returns date meta-data for the input images. It also improves the astrometric calibration of the image because the final astrometric calibration is performed at the appropriate epoch. The accuracy and reliability of Blind Date are functions of image size, pointing, angular resolution, and depth; performance is related to the sum of proper-motion signal-to-noise ratios for catalog stars measured in the input image. All of the science-quality images and 85 percent of the low-quality images in our sample of photographic plate images of M44 have their dates reliably determined to within a decade, many to within months.