Moon Phase Screensaver
The Moon Phase screensaver shows tonight's real lunar phase, calculated from the current date and shaded in 3D against a field of twinkling stars. It computes how far the Moon is through its 29.53-day cycle right now, so the slice of light you see matches the actual sky, and it labels the phase name and percent illuminated. It is free, runs in your browser with no download, and you press ESC to exit.
How the Phase of the Moon screensaver works
The screensaver converts the current time to a Julian date, then measures the Moon's age against a known new moon and the synodic month of 29.53058867 days. Dividing the age by that period gives a phase fraction from 0 (new) through 0.5 (full) back to 1 (new).
That fraction drives the lighting direction. A light vector is derived from the phase angle and used to shade a sphere pixel by pixel: each point's illumination is the dot product of its surface normal with the light, so the lit crescent or gibbous matches the real phase. Because the date is read locally, no internet connection is needed.
Surface detail is faked tastefully — a handful of craters darken small regions and limb darkening dims the edges of the disc for a rounded, three-dimensional look. The lit areas are tinted with the Moon color you choose.
When the label is enabled, it derives a phase name (New, Waxing Crescent, First Quarter, and so on) from the same fraction, computes the illuminated percentage, and prints today's full date underneath.
A worked example
With the defaults — Moon color #e8e6d8, Show phase name on, Glow on, and a Sky color of #05060f — the Moon hangs slightly above center, drifting gently, with its current phase name and a line like "78% illuminated" plus today's date beneath it. The warm off-white disc sits inside a soft halo against the deep-blue night sky. Turn Show phase name off for a clean, label-free Moon, or change the Sky color to recolor the night.
Settings & tips
- Leave Show phase name on to display the phase label, percent illuminated and today's date; turn it off for just the Moon.
- Pick a warmer or cooler Moon color to tint the lit surface to your taste.
- Adjust the Sky color and toggle Glow to set how much the Moon stands out from the night.
Frequently asked questions
- Does the moon phase screensaver show tonight's real moon?
- Yes. It computes the Moon's current age from today's date and the 29.53-day lunar cycle, so the phase shown matches the real Moon in the sky.
- Does the moon phase screensaver need the internet?
- No. The phase is calculated locally from your device's date and clock, so it works fully offline with no connection required.
- Does it show the percent of the moon that is illuminated?
- Yes. When the label is on, it prints the phase name, the percent illuminated, and today's full date beneath the Moon.
- Is the moon phase screensaver free?
- Yes. It is completely free with no download or sign-up. It runs in your browser and you press ESC to exit.
- Can I hide the phase name and percentage?
- Yes. Turn off the Show phase name toggle to display just the shaded Moon with no text labels.