What is a FITS Image File? I have few astronomical photos on my computer that have FITS Image File format. How do I view it? Are there FITS Image Viewer that are available for free on the internet?

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The Universe is full of magical things patiently waiting for our wits to grow sharper.

It stands for Flexible Image Transport System and is the main scientific file format for images though I've seen other types of data handled by it as well.

For amateur use it is the main format for CCD imaging. Usually in the form of 16 or 32 unsigned bit format.

To read up on it see:
http://fits.gsfc.nasa.gov/fits_intro.html

IRIS is a free CCD image processing program you can download that would display a image file.
http://www.astrosurf.com/buil/us/iris/iris.htm

If you have Adobe Elements (any version) or Photoshop you can use a free plugin called FITS Liberator.
http://www.spacetelescope.org/projects/fits_liberator/

Note that sometimes images loaded by these programs will be mirror reversed due to reading the file from the bottom instead of the top or visa versa. Just do a vertical flip when this happens.

Rick

You can try one of these http://www.nrao.edu/software/fitsview/

The GIMP as it is called, also reads FITS and allows you to read or convert about any image format currently in use today as well as lots of manipulations such as stacking, animations, enhancements, filtering, etc.

http://www.gimp.org/

Best regards,
Veeger