Description:
This routine retrieves the UTSTART and UTDATE values from the FITS array and calculates the MJD
from these. It can corrects for the time taken before beginning the observation by comparing the LST
stored in the header (written when the observation begins and before the telescope gets on source)
and the reference LST supplied to the routine (which is assumed to be the LST when the data
acquisition starts).
Invocation
CALL SCULIB_GET_MJD(N_FITS, FITS, MJD, STATUS)
Arguments
N_FITS =
_INTEGER (Given)
Size of FITS array
FITS = _CHARACTER (Given)
FITS values
LST_REF = DOUBLE PRECISION (Given)
Reference LST. This is the LST at which data
acquisition begins. The MJD should be calculated for the start of data taking rather than the
time the telescope begain its slew. This number is normally read from the LST_STRT array
and should be in radians. If a negative value or a zero value is given it is assumed that no
correction should be applied. This does mean that LST_REF can never be exactly zero but that
is thought be a remarkably unlikely event.
MJD = DOUBLE PRECISION (Returned)
Modified Julian date of observation
EPOCH = _REAL (Returned)
Epoch of observation
STARTUP_TIME = REAL (Returned)
The time taken, in seconds, for the observation to
begin. If the time stored in the STSTART is larger than LST_REF the assumption is that a
day boundary has been crossed since the LST_REF should always be more recent than
STSTART (the data can not be taken before the observation starts). A startup time longer than 5
minutes or so should be treated with suspicion. If the startup time is longer than 10 minutes
it is not used for the MJD calculation since this should never be the case. Set to zero if
LST_REF was negative.
STATUS = _INTEGER (Given & Returned)
Global status
Notes:
Uses the UTDATE and UTSTART and STSTART FITS headers. These must be present.
-
The date must be stored in UTDATE in format YYYY:M:D
-
The time must be stored in UTSTART in format HH:MM:SS.SS
-
The MJD is calculated for the start of data taking rather than simply using the values stored in
UTSTART. This is because there is always a delay between writing the FITS headers and taking data.
Copyright
Copyright ©1995-2000 Particle Physics and Astronomy Research Council. All Rights
Reserved.