UNIONS brings together more than 200 astronomers from the international community and is a close collaboration of three major Hawaii-based facilities – the Subaru Telescope, Pan-STARRS, and the Canada-France-Hawaii Telescope (CFHT) – to enable a tremendous breadth of new science in the era of survey astronomy. The UNIONS collaboration operates through a memorandum of understanding between:

• CFIS (Canada-France Imaging Survey), a collaboration composed of approximately 150 scientists mostly from Canada and France.
• Pan-STARRS (Panoramic Survey Telescope And Rapid Response System), a small group of astrophysicists at the Institute for Astronomy at the University of Hawaii responsible for the funding and scientific operation of Pan-STARRS including the Pan-STARRS1 and Pan-STARRS2 Telescopes, instruments, and associated cyber-infrastructure.
• WISHES (Wide Imaging with Subaru HSC of the Euclid Sky), a group of approximately 20 Japanese astronomers who submitted, with success, in 2020 a proposal of a Subaru Telescope open use intensive program to observe the northern sky with Subaru Hyper Suprime-Cam in the z-band.

New science is enabled by combining the CFIS u & r from CFHT-MegaCam imaging with i imaging from Pan-STARRS, z imaging from WISHES using Subaru Hyper Suprime-Cam (HSC), and g band imaging using Canadian and University of Hawaii access by UNIONS co-leads to Subaru HSC through the Waterloo Hawaii IfA G-band Survey (WHIGS). The Canadian Astronomy Data Centre (CADC) provides logistic support for processing and distributing the UNIONS products, from raw images to advanced catalogs.

A critical part of the original motivation to obtain these data was provided by opportunities relating to the Euclid mission. However, UNIONS exists as an entirely separate entity from Euclid, and has a strategic purpose and expected impact extending far beyond the Euclid mission.