Moon and Darkness Calendar

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Please enter a location or click the "Use My Location" button.

Help and Details

About

This Moon and Darkness Calendar is designed to help astronomers, astrophotographers, and night sky enthusiasts plan their observations. It provides a visual representation of darkness levels and moon phases, helping users identify optimal times for various types of night sky activities.

Each day-row focuses on a night, which is defined as a 24h period from 12:00 (noon) to 12:00 on the next day, while most other tools/tables/websites use calendar-days, so a 24h period from 00:00 to 24:00.

Using the Calendar

  1. Enter a location or use your current location.
  2. Set a start date and number of days to display.
  3. Hover over a day row to see hour-lines and inline times.
  4. Click on a day row to see detailed information for that night.
  5. Use the "Show inline times" option to display key times directly on the bars.
  6. Use the "Show hour lines" option to display vertical hour markers.
  7. Use the "Show max Moon altitude" option to display the Moon's maximum altitude for that night.

Darkness Levels

The darkness levels are calculated using the sun's altitude above the horizon.

  • Day: Sun's altitude > 0°. Full daylight.
  • Civil Twilight: Sun's altitude between 0° and -6°. There's enough light for objects to be clearly distinguishable. Brightest stars become visible.
  • Nautical Twilight: Sun's altitude between -6° and -12°. The horizon is no longer visible. Many stars used for celestial navigation are visible.
  • Astronomical Twilight: Sun's altitude between -12° and -18°. The sky is dark enough for most astronomical observations, but some twilight still interferes with more sensitive observations.
  • Astronomical Night: Sun's altitude < -18°. The darkest part of the night. Ideal for deep-sky observations and astrophotography.

These calculations take into account atmospheric refraction, which causes the sun to appear slightly higher than it actually is.

Moon Information

The moon information includes several key details:

  • Moon Phase: The current phase name, illumination percentage, and moon age in days (based on the 29.53-day lunar cycle).
  • Moonrise: Rise time is when the moon first starts to be visible above the horizon, including its azimuth (direction) and altitude.
  • Moon Culmination: Time when the moon reaches its highest point in the sky, including azimuth and altitude.
  • Moonset: Set time is the moment when the moon appears to vanish below the horizon, including its azimuth and altitude.
  • Moon Distance: The distance between Earth and moon in kilometers, with a percentage comparison to the average distance (384,400 km).

The visual representation in this calendar uses a grayscale gradient to indicate moon brightness, with darker shades representing a less bright moon and lighter shades a brighter moon. The moon is considered "invisible" when it's below the horizon, which is calculated based on the moon's altitude being negative.

Note: Actual visibility can be affected by local conditions such as weather, light pollution, and the observer's dark adaptation, which are not accounted for in these calculations.

Overlap Bar

The green overlap bar indicates periods when both astronomical darkness and moon invisibility occur simultaneously. These are optimal times for deep-sky observation.

Weekend Nights

Weekend nights (Friday and Saturday) are highlighted with a slight green tint for easy identification of potentially more convenient observation times.

Feedback

If you have any suggestions, feature requests, or encounter any issues, please don't hesitate to reach out. You can contact me via astro@dersphere.de

Changelog

  • Version 2.5 (14.11.2024): Add print button and layout for print and saving as PDF.
  • Version 2.4 (12.11.2024): Visually highlight midnight and major hour lines.
  • Version 2.3 (02.11.2024): Added max Moon altitude as inline text, save options in localStorage.
  • Version 2.2 (28.10.2024): Switch to astronomy.browser as the underlying library for more precise moon calculations.
  • Version 2.1 (26.10.2024): Added date to moon times, added moon age. Removed moon illumination angle.
  • Version 2.0 (24.10.2024): Rewrite. Added inline-times, hour-lines, overlap-bar, and replace tooltips with a daily detail section.
  • Version 1.2 (20.10.2024): Added gradient for moon illumination.
  • Version 1.1 (19.10.2024): Added tooltip with times for darkness and moon visibility.
  • Version 1.0 (19.10.2024): Initial release with basic darkness and moon phase calendar functionality.