DASCH: Bringing 100+ Years of Photographic Data into the 21st Century and Beyond
Peter K. G. Williams
The Harvard College Observatory was the preeminent astronomical data center of the early 20th century: it gathered and archived an enormous collection of glass photographic plates that became, and remains, the largest in the world. For nearly twenty years DASCH (Digital Access to a Sky Century @ Harvard) has been actively digitizing this library using a one-of-a-kind plate scanner. Earlier this year, after 470,000 scans, the DASCH project finished. Now, this unique analog dataset can be integrated into 21st-century, digital analyses. The key DASCH data products include ~350 TB of plate images, ~50 TB of calibrated lightcurves, and a variety of supporting metadata and calibration outputs. Virtually every part of the sky is covered by thousands of DASCH images with a time baseline spanning more than 100 years; most stars brighter than B ~ 15 have hundreds or thousands of detections. I will present the DASCH data release and discuss some of the lessons learned while trying to make data from the previous century accessible in the next century and beyond.