Hi!
I've recently become a bit unsure about the variable "Observation time". In setting up a telescope, I choose Observation time to be "Start of observation". This resonates with the Fits keyword "DATE-OBS" that my system sets to be precisely UTC start of observation, see below:
DATE-OBS= '2021-02-14T22:28:49.117' / UTC start date of observation
COMMENT Generated by INDI
JD_SOBS = 2459260.4366795835 / Julian Date at start of exposure
JD_UTC = 2459260.4368531946 / Julian Date (UTC) at mid-exposure
HJD_UTC = 2459260.4383482635 / Heliocentric JD (UTC) at mid-exposure
BJD_UTC = 2459260.439167416 / Barycentric JD (TDB) at mid-exposure
ALT_OBJ = 46.40646191754048 / Target altitude at mid-exposure
AZ_OBJ = 284.3220486102973 / Target azimuth at mid-exposure
HA_OBJ = 4.538689932234526 / Target hour angle at mid-exposure
ZD_OBJ = 43.59353808245952 / Target zenith distance at mid-exposure
RAOBJ2K = 4.4891266666666665 / J2000 right ascension of target (hours)
DECOBJ2K= 43.86745 / J2000 declination of target (degrees)
RA OBJ = 4.5138833699145255 / EOD right ascension of target (hours)
DEC OBJ = 43.9147107307991 / EOD declination of target (degrees)
However, as seen here, there is also a keyword with mid-exposure. Is there a risk of mixing things up here? Should I adjust my keywords or telescope setup? (could not find any detailed information on this in the VPhot user guide)
Magnus
Magnus:
VPhot reads the DATE-OBS header and EXPOSURE header to calculate the mid-exposure time/JD of your image magnitude, which is reported in the aavso report. It does not read the other headers you have in your image, which were input by your imaging software. BTW, what imaging software or other reduction software did you use (AIJ)? So you do not need to worry about these other header times.
The exception to this observation would be IF your software chose to report a mid time or end time in the DATE-OBS header, which is by FITS standard defined as the start time. If you look in your telescope setup window in VPhot, you will note that you can change this condition if needed. In your case, this would not be necessary.
HTH, Ken
Sorry for slow response…
Hi!
Sorry for slow response. Thanks! And yes, I use AIJ for calibration. Imaging with Ekos, calibrate with AIJ and measure and reduce with VPhot. I'd like to learn how to use some other software for reduction that I can run locally, like MPO Canopus, but slow learning there.
Magnus
Magnus:
I'd strongly recommend LesvePhotometry for your local reduction. It is free (shareware) but does require a full version of PinPoint which costs about $140.
Ken
…
Thanks, I'll check it out.
I would, however, prefer something for a Linux environment, since that is what I run on my desktop (Ubuntu). I've been looking at Munipack too, anyone using that?
Magnus