To celebrate Spitzer's 16th birthday, the Hubble Space Telescope team decided to put together a special present for their fellow "observing buddy."
Hubble and Spitzer have observed many of the same astronomical objects over the years; and with Spitzer getting data from infrared, and Hubble getting data from visible, ultraviolet, and some near-infrared, the two telescopes have helped uncover some of the mysteries of the universe.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 126.96.36.199.0