The Ska engineering telemetry archive tools support a wide range of formats for representing date-time stamps. Note that within this and other documents for this tool suite, the words ‘time’ and ‘date’ are used interchangably to mean a date-time stamp.

The available formats are listed in the table below:

Format	Description	System
secs	Elapsed seconds since 1998-01-01T00:00:00	tt
numday	DDDD:hh:mm:ss.ss… Elapsed days and time	utc
jd*	Julian Day	utc
mjd*	Modified Julian Day = JD - 2400000.5	utc
date	YYYY:DDD:hh:mm:ss.ss..	utc
caldate	YYYYMonDD at hh:mm:ss.ss..	utc
fits	FITS date/time format YYYY-MM-DDThh:mm:ss.ss..	tt
unix*	Unix time (since 1970.0)	utc
greta	YYYYDDD.hhmmss[sss]	utc

* Ambiguous for input parsing and only available as output formats.

For the date format one can supply only YYYY:DDD in which case 12:00:00.000 is implied.

The default time “System” for the different formats is either tt (Terrestrial Time) or utc (UTC). Since TT differs from UTC by around 64 seconds it is important to be consistent in specifying the time format.