Airmass in FITS Header

I wish to propose that an additional tag for Airmass in the FITS header is inserted. Airmass is an important attribute to whoever who do scientific imaging.

To generate variable star reports, the AAVSO extracts airmass from the FITS headers. However, due to the absence of this feature, the outcome that refers to airmass is zero. Airmass is important to know what kind of atmospheric conditions the observation was carried from.

Regards and thanks for the support to this great program,

MPC171 Flarestar Observatory

I would find this useful as well, as I occasionally do photometric observations as well with SGP.

Airmass and altitude have been added in

Many Thanks Ken. This feature will certainly make SGP more appealing to scientific imagers.

I will recommend SGP to my colleagues.


Sure thing. We do not have a formal background in scientific imaging (other than rudimentary knowledge of who does it and why they do it). If there are other metadata surrounding data collection (making the it more valuable) please let us know and we will do our best to add it in.

Question on the AirMass, just now getting time to play around with the release. I see the OBJCTALT, and the CENTALT keywords, but no AIRMASS. Am I missing something?


Sample Fits header from an image the other night.

SIMPLE = T / file does conform to FITS standard
BITPIX = 16 / number of bits per data pixel
NAXIS = 2 / number of data axes
NAXIS1 = 1391 / length of data axis 1
NAXIS2 = 1039 / length of data axis 2
RA = 274.695632677266 / Object Right Ascension in degrees
TELESCOP= ‘EQMOD ASCOM HEQ5/6’ / Telescope name
DEC = -13.8264494680851 / Object Declination in degrees
CRVAL2 = -13.8264494680851 / DEC at image center in degrees
CRVAL1 = 274.695632677266 / RA at image center in degrees
CCDYBIN = 1 / Camera Y Bin
SET-TEMP= 5.03 / Camera cooler temperature
CCD-TEMP= 5.03 / Camera cooler temperature
XBINNING= 1 / Camera X Bin
YBINNING= 1 / Camera Y Bin
CCDXBIN = 1 / Camera X Bin
PIXSCALE= 2.76294 / Image scale (arcsec / pixel)
SCALE = 2.76294 / Image scale (arcsec / pixel)
XPIXSZ = 6.44999980926514 / pixel size in microns (with binning)
YPIXSZ = 6.44999980926514 / pixel size in microns (with binning)
ANGLE = 8.26999999999998 / Image angle
OBJCTDEC= ‘-13 49 35.218’ / Object Declination in degrees
OBJCTRA = ‘18 18 46.952’ / Object Right Ascension in hms
OBJCTALT= 41.2289170792739 / Altitude of the object
FLIPPED = F / Is image flipped
CENTALT = 41.2289170792739 / Altitude of the object
DATE-LOC= ‘2015-09-03T21:58:03’ / Local observation date
OBJECT = 'M16 ’ / Object name
DATE-OBS= ‘2015-09-04T02:58:03’ / UTC observation date
CREATOR = ‘Sequence Generator Pro v2.4.2.10’ / Capture software
IMAGETYP= 'LIGHT ’ / Type of frame
CTYPE2 = ‘DEC–DEF’ / standard system and projection
BSCALE = 1 / default scaling factor
BZERO = 32768 / offset and data range to that of unsigned short
CRPIX1 = 695 / reference spectrum pixel coordinate for axis 1 CTYPE1 = ‘RA—DEF’ / standard system and projection
CRPIX2 = 519 / reference spectrum pixel coordinate for axis 2
FOCTEMP = 19.4992784992785 / Focuser temperature
FOCPOS = 6123 / Absolute focuser position
FWHEEL = ‘Atik FilterWheel EFW2’ / Filter Wheel name
EXPOSURE= 300 / Exposure time in seconds
FILTER = 'B ’ / Filter name
FOCUSER = ‘Moonlite DRO Focuser Driver’ / Focuser name
SITENAME= ‘Barn Owl Observtory’ / Observatory name
INSTRUME= ‘Atik Camera’ / Instrument name
SITEELEV= 100 / Elevation of the imaging site in meters
SITELONG= ‘95d33m20.000s’ / Longitude of the imaging site in degrees
SITELAT = ‘31d37m17.000s’ / Latitude of the imaging site in degrees

No. Looks like between testing and release, we busted AIRMASS.

Implemented in 2.4.2, fixed in

That fixed my AIRMASS value, its showing up now, thanks.


Yesterday, I had the chance to try out for the first time, the airmass feature added to SGP. AAVSO analysis of the data acquired through the latest SGP release now shows the airmass reference. I wish to convey my thanks to Ken for this valuable feature.

I have attached a sample summary of the results obtained through the observation of superhumps of the cataclysmic variable LQ Pegasi. My previous airmass results were always a strait line (no data) …not any more :smile:

Many Thanks & Regards,

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