Darkest Hours Planner

This program calculates when the darkest hours will be. This is the time from (1) the end of evening astronomical twilight to (2) the start of morning astronomical twilight, when (3) the moon is not up, for a given month and location.

These times are absolute, and should be taken with a grain of salt. For example, a two-day-old moon does not spoil the sky darkness much even when it is up!

Directions:
Enter the decimal latitude and longitude of your observing location the boxes below. Also, change the time zone, month and year if the defaults are not suitable. The defaults are the current month and year, and the location of the French Creek observing site near Warwick, PA ,USA.

Note that US daylight savings time is automatically accounted for.