McA FITS Format

FITS data

  • main fits image data (2d array), cropped to extend 0-360 degrees in longitude (only data from one CROT). Can be used for analysis in conjunction with header information as described below
  • fits extension 1 (extname='FULL') Uncropped image data (2d array). Longitude range (-30: 390) -- includes 30 degrees longitude data from preceding and following CROTs (used in some plot choices)
  • fits extension 2 (extname='LONG') Longitude data: array of 421 values which contain grid location of longitudes from -30 to 390 (degrees inclusive). Defines horizontal axis of 2d grid in uncropped image data.
  • fits extension 3 (extname='LAT') Latitude data: array of 181 values which contain grid location of latitudes from 0 to 180 (degrees inclusive). Defines vertical axis of 2d grid in uncropped image data.
  • fits extension 4 (extname='POL') Polarity data: 2d array of polarity (-1, 0, +1) corresponding to each point in the uncropped image data ('FULL')

Note: most images are scaled to a uniform no-resolution-lost scale. However, some cases from early in SC23 are not scaled, although they have very similar resolution to the uniform choice. This will not affect analysis since the header contains all the information necessary to do the analysis.

 

Standard FITS header variables

cunit1:'degrees'
cunit2:'degrees'
ctype1:'Longitude'
ctype2:'Latitude'
cdelt1: (1/pixel size horizontal)
cdelt2: (1/pixel size horizontal)
crpix1: bottom left pixel horizontal position (set to 0)
crpix2: bottom left pixel vertical position (set to 0)
crval1: bottom left pixel horizontal value degrees longitude (set to 0)
crval2: bottom left pixel vertical value degrees latitude (set to -90)
naxis1: number of array points horizontal dimension (varies)
naxis2: number of array points vertical dimension (varies)
origin: fits file name
date_obs: Carrington rotation begin date
B0: Solar B angle Carrington rotation begin date
L0: Carrington longitude Carrington rotation begin date
r_sun: Distance to Sun Carrington rotation begin date
rsun: Same as r_sun -- FITS headers differ on convention for this name so using both

 

Additional FITS header variables

angledeg: this is angle in degrees original was rotated
northint: this is vertical distance in original scan pixels to top edge of map from bottom of (rotated) scanned image
southint: this is vertical distance in original scan pixels to bottom edge of map from bottom of scanned image
eastint: this is horizontal distance in original scan pixels to right edge of map from left of scanned image
westint: this is horizontal distance in original scan pixels to left edge of map from left of (rotated) scanned image
scalingx: ratio of standard horizontal pixel to original scanned pixel
scalingy: ratio of standard verticall pixel to original scanned pixel
scaling: average of scalingx and scalingy
northinter_scale: vertical intercept distance for a scaled map. For most cases this will identical to northinter, however, if not, it indicates an image that has not been scaled to the standard uniform scaling. Note that the only difference this makes to the maps is that the size of boundary lines will be slightly different for unscaled maps, since they were scaled to image pixel in Photoshop. It is a small effect, and does not affect lat-lon position of features and so should not affect analysis at all.
tm6060, tm60300, tm90180, tm12060, tm120300: average latitude position of pixels lying in the vicinity of latitude 60, longitude 60 (etc) in original grid (can be used along with others to follow to measure distortion in scan)
ts6060, ts60300, ts90180, ts12060, ts120300: standard deviation of latitude of pixels lying in the vicinity of latitude 60, longitude 60 (etc) in original grid
nm6060, nm60300, nm90180, nm12060, nm120300: average of longitude of pixels lying in the vicinity of latitude 60, longitude 60 (etc) in original grid
ns6060, ns60300, ns90180, ns12060, ns120300: standard deviation of longitude of pixels lying in the vicinity of latitude 60, longitude 60 (etc) in original grid

 

FITS extensions header variables

fullax1: number of pixels in extended image (horizontal)
fullax1: number of pixels in extended image (vertical)