Representations of time coordinates in FITS

Time and relative dimension in space

¹ Harvard-Smithsonian Center for Astrophysics/Smithsonian Astrophysical Observatory, 60 Garden Street MS 67, Cambridge, MA 02138, USA
e-mail: arots@cfa.harvard.edu
² Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
³ CSIRO Astronomy and Space Science, PO Box 76, Epping NSW 1710, Australia
⁴ UCO/Lick Observatory, University of California, Santa Cruz, CA 95064, USA
⁵ Adnet Systems, Inc., NASA Goddard Space Flight Center, Code 671, Greenbelt, MD 20771, USA

Received: 22 July 2014
Accepted: 26 September 2014

Abstract

Context. In a series of three previous papers, formulation and specifics of the representation of world coordinate transformations in FITS data have been presented. This fourth paper deals with encoding time.

Aims. Time on all scales and precisions known in astronomical datasets is to be described in an unambiguous, complete, and self-consistent manner.

Methods. Employing the well-established World Coordinate System (WCS) framework, and maintaining compatibility with the FITS conventions that are currently in use to specify time, the standard is extended to describe rigorously the time coordinate.

Results. World coordinate functions are defined for temporal axes sampled linearly and as specified by a lookup table. The resulting standard is consistent with the existing FITS WCS standards and specifies a metadata set that achieves the aims enunciated above.