The data files at the NASA Astronomy Data Center are in .gz format. What is this, and how do I use it on a PC?

These files are in compressed binary format, and need to be 'unzipped' using either the UNIX 'tar' utility or the equivalent on VAX\VMS machines. The ADC also offers a CD-ROM set in which the ASCII versions of all catalogs are also present. I believe these ASCII catalog sets are also available online at the National Space Science Data Center located at the NASA Goddard Space Flight Center. Try sending email to the webmaster on the ADC homepage.