Astronomers use telescopes that are based all around the world and even in space. Every telescope is different but the data that they take is the same. A lot of these files are now stored online in archives. These bring together observations from telescopes around the world. There are millions of images which can be accessed by anyone for free.

To help researchers to use lots of different telescopes from all over the globe, a special kind of computer file was made. It is called a FITS file, which stands for the Flexible Image Transport System.

FITS files are usually a few megabytes in size. Even though it has the word 'image' in its name, you cannot open a FITS using common photo editing software. It may make more sense to think of a FITS as a document. As well as arrays of pixel data, it contains lots of other information. 

So how do you open a FITS to see your image? You need to use software or applications designed to read FITS files. We have created our own software that you can use free. But there are others you can use, including Makali'i.

In addition to the image itself, your FITS will contain the FITS header. This part of the file contains all the details about your observation. If you need to know what filters were used or what time your observation was taken, look in the FITS header. It may even include what the weather was like. 

The FITS header can contain pretty much whatever the astronomer wants. So bear in mind that different FITS headers may not all contain the same categories or levels of detail.These files store the actual images. FITS images can be used together with image display and photometry software.