What do the file names for the images and directories on the Voyager CD-ROMs mean?
On the Voyager imaging CD-ROMs, the top level directories indicate the object name, for example Jupiter, Saturn, Rings, Oberon. Under that lies directories with names like CnnnnXXX and, under each of these directories, lie images with names like Cnnnnmmm. These file names are derived from the actual exposure numbers, which are of the form xxxxx.yy. For the Voyager Imaging Science Subsystem (ISS), each exposure is tagged with the current spacecraft clock time. Because the spacecraft clock time is measured in seconds from launch, the number is quite large and gets larger as time goes by. Rather than having to deal with extraordinarily large numbers, the time is reduced in two ways to come up with the exposure number. First, the time is taken modulo 65,536 (16 bit) to come up with the first five digits of the exposure number (which, padded appropriately with zeros on the left becomes the xxxxx part). Second, the time is taken modulo 60 to come up with the last two digits of the number (th
