CD1_1		 x degrees/pixel
CD2_2		 y degrees/pixel
CTYPE1 = RA-projection
CTYPE2 = DEC-projection
CRVAL_1	 degrees in ra
CRVAL_2		  degrees in dec
CRPIX1				   x coordinate reference pixel
CRPIX2				      y coordinate reference pixel


ORIENT
CROTA
ROTATE

KEYWORD:    ORIENTAT
REFERENCE:  STScI    
HDU:        image
DATATYPE:   real
COMMENT:    position angle of image y axis (deg. E of N)
DEFINITION: The value field shall contain a floating point number giving
the position angle of the y axis of the detector projected on the sky,
in degrees east of north. This keyword is synonymous with the CROTA2 WCS
keyword.