Free · Find the darkest sky window

Astronomical Darkness Planner

Find when astronomical night starts, ends, and reaches its darkest point.

  • SunCalc 2 astronomy
  • Private in your browser
  • JSON and CSV downloads

Find dark sky time

Use the sample place or enter coordinates. All times use the chosen time zone.

1
Choose place and timeCoordinates stay on this device
2
Read the sky planToronto · America/Toronto
Your local result will appear hereUse the sample place, then press the gold button.

Three simple steps

How to use it

  1. Choose a place and date.
  2. Read the full darkness window.
  3. Check the moon and weather before stargazing.

Your place stays on this device

SunCalc does the sky math inside this browser tab. Bookify does not upload or save coordinates, dates, or times. Results assume a clear, level horizon; terrain, weather, and buildings can change what you see.