1. Allen, S., & Wells, D. 2005, IETF RFC 4047, http://www.ietf.org/rfc/rfc4047.txt
2. ANSI 1977, American National Standard for Information Processing: Code for Information Interchange, ANSI X3.4–1977 (ISO 646), New York: American National Standards Institute, Inc.
3. Bradner, S. 1997, IETF RFC 2119, http://www.ietf.org/rfc/rfc2119.txt
4. Bunclark, P., & Rots, A. 1997, Precise re-definition of DATE-OBS Keyword encompassing the millennium, http://fits.gsfc.nasa.gov/year2000.html
5. Representations of celestial coordinates in FITS