How to use Sun/Moon Times & Dark Window

Tool walkthrough · 0:45 · silent, with on-screen words

A walkthrough of the Dark Window tool at Georgetown, recorded from the real tool: a new-Moon night with nearly ten dark hours, against a Full Moon night with none.

The video file (MP4, 2017 kB)

Shows the Dark Window tool at Georgetown for the nights of 10 October 2026 (new Moon) and 25 October 2026 (Full Moon), Guyana time.

Chapters

  1. 0:04 Place and date
  2. 0:10 Sunset and twilight
  3. 0:17 The dark window
  4. 0:25 A Full Moon night

From the lesson How to Use Sun/Moon Times & Dark Window.

What the video shows, in words

A silent walkthrough recorded from the real Sun/Moon Times & Dark Window tool on this site, for Georgetown, Guyana, in Guyana time, with the cursor and on-screen words showing each step.

On 10 Oct 2026 (New Moon · 0% lit) the Sun sets at 5:40 PM, astronomical darkness runs from 6:49 PM to 4:30 AM, and the dark window is 9h 41m, from 6:49 PM to 4:30 AM. On 25 Oct 2026 (Full Moon · 100% lit, rising at 5:08 PM, before sunset at 5:34 PM) there is no moonless astronomical darkness.

  1. 0:00 The Dark Window tool finds the hours each night when the sky is fully dark and the Moon is down.
  2. 0:04 Pick the place and the night. Here: Georgetown, the night of 10 Oct 2026.
  3. 0:10 The Sun sets at 5:40 PM; astronomical darkness, the Sun 18° down, starts at 6:49 PM and ends at 4:30 AM.
  4. 0:17 With a New Moon the whole astronomical night is moonless: 9h 41m, from 6:49 PM to 4:30 AM.
  5. 0:25 Use today jumps to the frozen date, 25 Oct 2026: a Full Moon, 100% lit, rising at 5:08 PM.
  6. 0:34 A Full Moon is up all night, so there is no moonless darkness at all: plan deep-sky nights near new Moon.
  7. 0:41 Check the dark window before you drive out, and add it to your calendar.

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