Vol. Science · Astronomy · Luna

Moon
phases

Drag the dial (or use presets) to walk a synodic month — new through full and back. Illumination here is a simple geometric cartoon for learning names and sky brightness, not a precision ephemeris. Pair with the Campbell / Bay Area local sky and light pollution desk when planning faint-object nights.

Phase angle ≈ age / 29.53 × 360°. Real Moon also librates and has a ~5° orbital tilt (eclipses are special). Figures round NASA educational orders of magnitude.

Interactive · Phase dial

Handy numbers

Synodic month

~29.53 days — new Moon to new Moon as seen from Earth (phase cycle).

Sidereal month

~27.3 days — one orbit relative to the stars; shorter than the phase cycle.

Mean distance

~384,400 km · about 30 Earth diameters · light travel ~1.3 s.

Diameter

~3,475 km · roughly 1/4 Earth’s · gravity ~1/6 g on the surface.

Terminator

Day/night line on the Moon — best contrast for craters near first/last quarter.

Earthshine

Near new, the dark disk can glow faintly from sunlight reflected off Earth.

Observing from the South Bay

Keep going

Educational schematic. Phase names follow common Northern-hemisphere naming. Distances and periods round public NASA / USGS educational figures — not for navigation or eclipse prediction. Earthrise preview image: NASA / Bill Anders (public domain).