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diff --git a/noao/astutil/doc/setjd.hlp b/noao/astutil/doc/setjd.hlp new file mode 100644 index 00000000..c010d533 --- /dev/null +++ b/noao/astutil/doc/setjd.hlp @@ -0,0 +1,222 @@ +.help setjd Jan92 astutil +.ih +NAME +setjd -- set various Julian dates in image headers +.ih +USAGE +setjd images +.ih +PARAMETERS +.ls images +The list of images for which to compute Julian dates. If the \fIlistonly\fR +parameter is not set the image headers will be modified to add or update +the calculated Julian date values. +.le +.ls observatory = ")_.observatory" +Observatory of observation, used to define the time zone relative to +Greenwich, if not specified in the image header by the keyword OBSERVAT. +The default is a redirection to look in the parameters for the parent +package for a value. The observatory may be one of the observatories in +the observatory database, "observatory" to select the observatory defined +by the environment variable "observatory" or the parameter +\fBobservatory.observatory\fR, or "obspars" to select the current +parameters set in the \fBobservatory\fR task. See \fBobservatory\fR for +additional information. +.le +.ls date = "date-obs" +Date of observation keyword. The value must be in FITS format. +This is one of DD/MM/YY (old FITS format), YYYY-MM-DD (new FITS format), +or YYYY-MM-DDTHH:MM:SS (new FITS format with time). The date should be +in universal time though the \fIutdate\fR parameter can be used if +this is not the case. If a time is included it is used in preference +to the \fItime\fR value. +.le +.ls time = "ut" +Time of observation keyword with value given in decimal hours or HH:MM:SS.S +format. The date may be a local time or universal time as selected by the +\fIuttime\fR parameter. The time is used as is +unless an exposure time keyword is specified, in which case +the time will be corrected to the midpoint of the exposure from the +beginning or end of the exposure. This time is not used if a time +is given in the date keyword. +.le +.ls exposure = "exptime" +Exposure time keyword with value in seconds. If specified the time +is corrected to the midpoint of the exposure. The time is assumed +to be the beginning of the exposure unless +the exposure time keyword name begins with a minus sign, for example +"-exptime", in which case the time is used as the end of the exposure. +.le +.ls ra = "ra", dec = "dec", epoch = "epoch" +If the heliocentric Julian date is requested the right ascension (in hours) +and declination (in degrees) of the observation is determined from these +keywords. The values may be in either decimal or sexagesimal notation. +An epoch keyword is optional and if given is used to precess +the coordinates from the specified epoch to the observation epoch. +If an epoch keyword is given but is not found in the header or can't +be interpreted then it is an error. The epoch keyword value may begin +with 'B' or 'J'. If the value is before 1800 or after 2100 a warning +will be printed though the task will still compute the values. +.le + +.ls jd = "jd" +If specified compute the geocentric Julian day (Greenwich) at the +midpoint of the exposure and record the value in the specified +header keyword. +.le +.ls hjd = "hjd" +If specified compute the heliocentric Julian day (Greenwich) at the +midpoint of the exposure and record the value in the specified +header keyword. +.le +.ls ljd = "ljd" +If specified compute the local Julian day number. This is an integer +number which is constant for all observations made during the same night. +It may be used to group observations by night in such tasks as +\fBrefspectra\fR. +.le + +.ls utdate = yes, uttime = yes +Define whether the date and time of observation are in local standard +time or in universal time. +.le +.ls listonly = no +List the computed values only and do not modify the image headers. +When simply listing the images need not have write permission. +.le +.ih +DESCRIPTION +\fBSetjd\fR computes the geocentric, heliocentric, and integer +local Julian dates from information given in the headers of +the input list of images. This information may simply be listed or +the values may be added or modified in the image headers. Only +those values which have a keyword specified are computed, printed, +and entered in the images. Thus, one need not compute all values +and the dependent image header parameters required for computing them +need not be present. For example, if the coordinates of the +observation are not available one should set the \fIhjd\fR parameter +to an empty string. + +Often the date and time of observation are recorded either at the +beginning or the end of an exposure. To compute the Julian dates +at the midpoint of the exposure the exposure keyword is specified. +A negative sign preceding the keyword name defines correcting from +the end of the exposure otherwise the correction is from the +beginning of the exposure. The exposure time must be in seconds and +there is no allowance made for exposures which are interrupted. +See also the task \fBsetairmass\fR which may be used to compute a +universal time midexposure value. + +The date and time of observations should be given either in universal +time. However, if they are given in local standard time (there is no +provisions for daylight savings times) the \fIutdate\fR and \fIuttime\fR +parameters may be used. Conversion between local and universal times, as +well as the computation of the local integer date, requires the time zone +in (positive) hours behind Greenwich or (negative) hours ahead of +Greenwich. This information is determined from the observatory at which +the observations were made. If the observatory is specified in the image +header under the keyword OBSERVAT with a value which has an entry in the +NOAO, local, or user observatory database then the value from the database +is used. This is the safest way since the observatory is tied to the +actual image. Otherwise, the \fIobservatory\fR parameter defines the +observatory. The special value "observatory" allows defining a default +observatory with an environment variable or the \fBobservatory\fR task. +Explicitly use the parameter \fIobservatory.timezone\fR use the value +"obspars". For more information see help under \fBobservatory\fR. + +The heliocentric Julian date is computed by defining a keyword for +this value and also defining the keywords for the right ascension (in hours) +and declination (in degrees). An optional epoch keyword may be +used if the RA and DEC are not for the observation epoch. + +The local integer Julian day number is the Julian date which begins at +local noon. Thus, all observations made during a night will have the +same day number. This day number may be useful in grouping +observations by nights. Note that in some time zones the UT +date of observation may also be constant over a night. + +Among the uses for this task is to define keywords to be used by the task +\fBrefspectra\fR. In particular, the exposure midpoint geocentric Julian +date makes a good sort parameter and the local Julian day number makes a +good group parameter. +.ih +EXAMPLES +1. Compute all the Julian date quantities for 4 arc exposures with +header parameters given below. + +.nf + demoarc1: + OBSERVAT= 'KPNO ' / observatory + EXPTIME = 60. / actual integration time + DATE-OBS= '26/11/91 ' / date (dd/mm/yy) of obs. + UT = '12:11:30.00 ' / universal time + RA = '06:37:02.00 ' / right ascension + DEC = '06:09:03.00 ' / declination + EPOCH = 1991.9 / epoch of ra and dec + + demoarc2: + OBSERVAT= 'KPNO ' / observatory + EXPTIME = 60. / actual integration time + DATE-OBS= '26/11/91 ' / date (dd/mm/yy) of obs. + UT = '12:41:30.00 ' / universal time + RA = '06:37:02.00 ' / right ascension + DEC = '06:09:03.00 ' / declination + EPOCH = 1991.9 / epoch of ra and dec + + demoarc3: + OBSERVAT= 'CTIO ' / observatory + EXPTIME = 60. / actual integration time + DATE-OBS= '27/11/91 ' / date (dd/mm/yy) of obs. + UT = '11:11:30.00 ' / universal time + RA = '06:37:02.00 ' / right ascension + DEC = '06:09:03.00 ' / declination + EPOCH = 1991.9 / epoch of ra and dec + + demoarc4: + OBSERVAT= 'CTIO ' / observatory + EXPTIME = 60. / actual integration time + DATE-OBS= '27/11/91 ' / date (dd/mm/yy) of obs. + UT = '12:21:30.00 ' / universal time + RA = '06:37:02.00 ' / right ascension + DEC = '06:09:03.00 ' / declination + EPOCH = 1991.9 / epoch of ra and dec + + cl> setjd demoarc?.imh + # SETJD: Observatory parameters for Kitt Peak ... + # Image JD HJD LOCALJD + demoarc1.imh 2448587.0083 2448587.0127 2448586 + demoarc2.imh 2448587.0292 2448587.0336 2448586 + # SETJD: Observatory parameters for Cerro Tololo ... + demoarc3.imh 2448587.9667 2448587.9711 2448587 + demoarc4.imh 2448588.0153 2448588.0197 2448587 +.fi + +Note the use of the observatory parameter to switch observatories and +the local Julian day number which is constant over a night even though +the Julian date may change during the observations. + +2. To compute only the geocentric Julian date from the "DATE" and +"TIME" keywords in an image, + +.nf + cl> setjd obs1 date=date time=time exp="" hjd="" ljd="" +.fi +.ih +REVISIONS +.ls SETJD V2.11.2 +Y2K update: Updated to use the new FITS format for the date. If the +time is given in the date keyword it is used in preference to the +time keyword. +.le +.ls SETJD V2.11 +The checking of the epoch keyword value was improved. Previously if +there was a problem with the keyword value (missing or malformed) the +task would use the epoch of the observation. Now it is an error +if an epoch keyword is specified but the epoch value can't be determined. +Also a leading 'B' or 'J' is allowed and a warning will be given if +the epoch value is unlikely. +.le +.ih +SEE ALSO +setairmass, hedit, refspectra, observatory +.endhelp |