The actual time scale used: TT, TAI, UTC, TDB, etc. astronTime may be expressed in ISO8601 or as a double relative to a reference time; or it may be provided in an entity refered to by the Reference element Only a limited subset of ISO 8601 is allowed: yyyy-mm-ddThh:mm:ss.sss... Note that this time may require precision that exceeds that of a double Note that this time may require precision that exceeds that of a double Relative time needs a time reference (a zero point) which should not be in relative time The time unit; only 's' (second - default) or 'd' (day) are allowed The reference time needs to be ISO8601, JD, or MJD; note: only a limited subset of ISO 8601 is allowed: yyyy-mm-ddThh:mm:ss.sss... Note that this time may require precision that exceeds that of a double Note that this time may require precision that exceeds that of a double The time unit has only meaning if relative time is used in the reference; only 's' (second - default) or 'd' (day) are allowed and a RefTime is required The time unit has only meaning if relative time is used in the reference; only 's' (second - default) or 'd' (day) are allowed The reference time needs to be ISO8601, JD, or MJD; only needed if time_base="relative" Note that this time may require precision that exceeds that of a double Note that this time may require precision that exceeds that of a double For vector coordinates we need arrays of doubles Coordinate units may be angular (degrees, radians, hours, arcmins, arcsecs), linear (meters, km, mm, AUs, parsecs, kpc, Mpc, lightyears), or empty (i.e., dimensionless) Angular coordinate units may be degrees, radians, hours, arcmins, arcsecs Velocity units are a posUnitType / velTimeType; the latter may be second, day, hour, year (a or yr), century, or empty Spectral units may be frequency (Hz, kHz, MHz, GHz), wavelength (meters, mm, micron, nm, Angstrom), or energy(eV, keV, MeV, GeV) A scalar time coordinate value consists of a double or a reference to an entity (that should contain a double) A scalar time coordinate value consists of a double or a reference to an entity (that should contain a double) A scalar coordinate value consists of a double, a sexagesimal string (requiring ':' separators), or a reference to an entity (that should contain a double or sexagesimal string) A coordinate vector of length 2 consists of either two doubles or two references (that should each contain one double) For vector coordinates we need arrays of doubles If empty, the value of pos1_unit is inherited; note that this construct is necessary: RA and Dec may have different units, such as h and deg A size (ellipse) in two coordinates contains: two doubles or two IDREFs, each with optional position angle; or a 2x2 matrix defining the ellipse For vector coordinates we need arrays of doubles For vector coordinates we need arrays of doubles If empty, the value of pos1_unit is inherited A coordinate vector of length 3 consists of either three doubles or three references (that should each contain one double) For vector coordinates we need arrays of doubles If empty, the value of pos1_unit is inherited If empty, the value of pos1_unit is inherited A size (ellipsoid) in three coordinates contains: three doubles or three IDREFs, each with two optional position angles; or a 3x3 matrix defining the ellipsoid For vector coordinates we need arrays of doubles For vector coordinates we need arrays of doubles For vector coordinates we need arrays of doubles If empty, the value of pos1_unit is inherited If empty, the value of pos1_unit is inherited This contains all the elements of a time coordinate: value, error, resolution, size, pixel size, unit, and name astronTime may be expressed in ISO8601 or as a double relative to a reference time; or it may be provided in an entity refered to by the Reference element A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) This contains all the elements of a spectral coordinate: value, error, resolution, size, pixel size, unit, and name astronTime may be expressed in ISO8601 or as a double relative to a reference time; or it may be provided in an entity refered to by the Reference element A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) This is the time part in the velocity unit; it is the same for al elements of the velocity coordinate This contains all the elements of a scalar coordinate: value, error, resolution, size, pixel size, unit, and name A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) This contains all the elements of a coordinate vector of length 2: value, error, resolution, size, pixelsize, unit, and names A coordinate vector of length 2 consists of either two doubles or two references (that should each contain one double) A size (ellipse) in two coordinates contains: two doubles or two IDREFs, each with optional position angle; or a 2x2 matrix defining the ellipse A size (ellipse) in two coordinates contains: two doubles or two IDREFs, each with optional position angle; or a 2x2 matrix defining the ellipse A size (ellipse) in two coordinates contains: two doubles or two IDREFs, each with optional position angle; or a 2x2 matrix defining the ellipse A size (ellipse) in two coordinates contains: two doubles or two IDREFs, each with optional position angle; or a 2x2 matrix defining the ellipse Unit of all position angles This contains all the elements of a coordinate vector of length 3: value, error, resolution, size, pixelsize, unit, and names A coordinate vector of length 3 consists of either three doubles or three references (that should each contain one double) A size (ellipsoid) in three coordinates contains: three doubles or three IDREFs, each with two optional position angles; or a 3x3 matrix defining the ellipsoid A size (ellipsoid) in three coordinates contains: three doubles or three IDREFs, each with two optional position angles; or a 3x3 matrix defining the ellipsoid A size (ellipsoid) in three coordinates contains: three doubles or three IDREFs, each with two optional position angles; or a 3x3 matrix defining the ellipsoid A size (ellipsoid) in three coordinates contains: three doubles or three IDREFs, each with two optional position angles; or a 3x3 matrix defining the ellipsoid Unit for all position angles This contains all the elements of a scalar coordinate: value, error, resolution, size, pixel size, unit, and name A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) A scalar coordinate value consists of a double or a reference to an entity (that should contain a double) This contains all the elements of a coordinate vector of length 2: value, error, resolution, size, pixelsize, unit, and names A coordinate vector of length 2 consists of either two doubles or two references (that should each contain one double) A size (ellipse) in two coordinates contains: two doubles or two IDREFs, each with optional position angle; or a 2x2 matrix defining the ellipse A size (ellipse) in two coordinates contains: two doubles or two IDREFs, each with optional position angle; or a 2x2 matrix defining the ellipse A size (ellipse) in two coordinates contains: two doubles or two IDREFs, each with optional position angle; or a 2x2 matrix defining the ellipse A size (ellipse) in two coordinates contains: two doubles or two IDREFs, each with optional position angle; or a 2x2 matrix defining the ellipse Unit for all position angles This contains all the elements of a coordinate vector of length 3: value, error, resolution, size, pixelsize, unit, and names A coordinate vector of length 3 consists of either three doubles or three references (that should each contain one double) A size (ellipsoid) in three coordinates contains: three doubles or three IDREFs, each with two optional position angles; or a 3x3 matrix defining the ellipsoid A size (ellipsoid) in three coordinates contains: three doubles or three IDREFs, each with two optional position angles; or a 3x3 matrix defining the ellipsoid A size (ellipsoid) in three coordinates contains: three doubles or three IDREFs, each with two optional position angles; or a 3x3 matrix defining the ellipsoid A size (ellipsoid) in three coordinates contains: three doubles or three IDREFs, each with two optional position angles; or a 3x3 matrix defining the ellipsoid Unit for all position angles The coordinate element consists either of a coordinate file or a sequence of time element, spatial coordinate element, velocity element, and redshift element; the spatial and velocity elements may be scalar or vector; it needs to refer to a coordinate system This contains all the elements of a time coordinate: value, error, resolution, size, pixel size, unit, and name This contains all the elements of the redshift coordinate: value, error, resolution, size, pixel size, unit, and name This contains all the elements of the spectral coordinate: value, error, resolution, size, pixel size, unit, and name