LST/GST/UTC clock program for Windows, with source

Last updated 2020 May 20

In 1998, I wrote a little C program to show Local Sidereal Time, Greenwich Sidereal Time, or Universal (Greenwich Mean) Time. It was written as a 16-bit program. In late 2007, I got an inquiry about it from a ham radio operator, who was interested in its ability to show Universal Time, but couldn't get it to work in Vista. I made some small revisions that turned it into a 32-bit program.

You can click here to download the source code and executable. lst64.exe is for 64-bit Windows; lst32.exe is for 32-bit Windows.

There is only a system menu; using it, you can switch from LST (the default) to GST or UTC. That's about the only control you have over what the program does.

For correct computation of LST, the program does need to know your longitude. To do this, edit the file lst.txt, and reset the longitude in that file accordingly. (This file also includes directions for adding an arbitrary time offset, useful on systems with odd time zone issues.)