3D array in FITS data I am an amateur astronomer currently working on Spitzer telescope dataset with python (astropy and aplpy). From the examples in astropy's website, I understood that the FITS data is a way to represent image data with human-readable headers.  However, I now have a fits image ( SPITZER_I2_46469632_0000_0000_2_bcd.fits ) which is a 3D array of dimensions (64, 32, 32). I believe the second and third coordinates to be the length and height of the image in pixels. What about the first dimension? How do I interpret such images and NaNs in the data?
It appears to me that the full Spizter frame should normally be 256x256 but, if observing a very bright source or when requiring high temporal resolution, a different observing mode is performed wherein only 32x32 pixels are read from the CCD. However, what happens is that the exposure times are short and a total of 64 frames are observed in total, creating a data cube of 64x32x32. If you want, you can treat each individial 32x32 frame as its own image, or else stack them all together for the full image.

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