Lunar Co-longitude

Colong.exe is a Windows 95/98/NT/Me/2000/XP program which displays the lunar colongitude (position of the morning terminator) for dates between 1989 and 2020. The program uses the Date and Time Zone settings in Windows 95/98/NT to compute and display local time and UTC, automatically compensating for Daylight Savings Time. (See screen shot at bottom of page)

The program is free, but the author reserves all rights. To minimize download time, Colong.exe is stored as


Colong.exe was named the winner of the 1998 Computing Challenge Award of the Computing Section of the Association of Lunar and Planetary Observers:

Computing Challenge Award

program display

The Firefighter Calendar is now maintained at