Table 5
Keywords for specifying time coordinates.
| Keyword description | Section | Global | Images | Table pixel columns | Table vector columns | |||
| Single | Multiple | Primary | Alternate | Primary | Alternate | |||
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| 5.a Informational keywords | ||||||||
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| Date of HDU creationa | 4.4 | DATE | ||||||
| Date/time of observation | 4.4 | DATE-OBS | DOBS n | DOBS n | ||||
| MJD-OBS | MJDOB n | MJDOB n | ||||||
| JEPOCH | ||||||||
| BEPOCH | ||||||||
| Effective date/time of observation | 4.4 | DATE-AVG | DAVG n | DAVG n | ||||
| MJD-AVG | MJDA n | MJDA n | ||||||
| Start date/time of observation | 4.4 | DATE-BEG | ||||||
| MJD-BEG | ||||||||
| TSTART | ||||||||
| End date/time of observation | 4.4 | DATE-END | ||||||
| MJD-END | ||||||||
| TSTOP | ||||||||
| Net exposure time | 4.6 | XPOSURE | ||||||
| Wall clock exposure time | 4.6 | TELAPSE | ||||||
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| 5.b Global time reference frame keywords and their optional context-specific override keywords | ||||||||
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| Time scalec | 4.1.1 | TIMESYS | CTYPE i d | CTYPE ia d | TCTYP n d | TCTY na d | i CTYP n | i CTY na |
| Zero point in MJD | 4.1.2 | MJDREF b | ||||||
| Zero point in JD | 4.1.2 | JDREF b | ||||||
| Zero point in ISO-8601 | 4.1.2 | DATEREF | ||||||
| Reference position | 4.1.3 | TREFPOS | TRPOS n | TRPOS n | ||||
| Reference direction | 4.1.4 | TREFDIR | TRDIR n | TRDIR n | ||||
| Solar System ephemeris | 4.1.5 | PLEPHEM | ||||||
| Time unit | 4.2 | TIMEUNIT | CUNIT i | CUNIT ia | TCUNI n | TCUN na | i CUNI n | i CUN na |
| Time offset | 4.3.1 | TIMEOFFS | ||||||
| Absolute Error | 4.3.2 | TIMSYER | CSYER i | CSYER ia | TCSYE n | TCSY na | i CSYE n | i CSY na |
| Relative Error | 4.3.3 | TIMRDER | CRDER i | CRDER ia | TCRDE n | TCRD na | i CRDE n | i CRD na |
| Time resolution | 4.3.4 | TIMEDEL | ||||||
| Time location in pixel | 4.3.5 | TIMEPIXR | ||||||
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| 5.c Additional context-specific keywords for the time reference frame | ||||||||
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| Time axis name | 6.2 | CNAME i | CNAME ia | TCNAM n | TCNA na | i CNAM n | i CNA na | |
| Time axis reference pixel | 6.2 | CRPIX i | CRPIX ia | TCRPX n | TCRP na | i CRPX n | i CRP na | |
| Time axis reference value | 6.2 | CRVAL i | CRVAL ia | TCRVL n | TCRV na | i CRVL n | i CRV na | |
| Time scaling | 6.2.3 | CDELT i | CDELT ia | TCDLT n | TCDE na | i CDLT n | i CDE na | |
| Period for temporal phasee | 4.5 | CPERI i | CPERI ia | TCPER n | TCPR na | i CPER n | i CPR na | |
| Zero phase timee | 4.5 | CZPHS i | CZPHS ia | TCZPH n | TCZP na | i CZPH n | i CZP na | |
| Transformation matrix | 6.2.3 | CD i _ j | CD i _ ja | TC n _ ka | ij CD na | |||
| Transformation matrix | 6.2.3 | PC i _ j | PC i _ ja | TP n _ ka | ij PC na | |||
Notes.
These keywords maybe split into an integer (MJDREFI or JDREFI) and fractional (MJDREFF or JDREFF) part.
These keywords may also assume the values PHASE, TIMELAG, or FREQUENCY to specify the corresponding time-related coordinate axes (see Sect. 4.5).
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