Move the Moon first, then compare direct sunlight, reflected moonlight and real shadow geometry. Yellow lines are direct sunlight, blue lines are reflected light toward Earth, and translucent cones are shadows.
The Sun is the dominant visible light source in this system. Sunlight arrives from one direction, illuminating the lunar hemisphere that faces the Sun while the opposite hemisphere is in lunar night.
The lunar surface is rough, not a mirror. Incoming sunlight is scattered in many directions; only a small fraction travels toward Earth. That reflected sunlight enters our eyes and is what we call moonlight.
Earth and Moon both cast shadow cones away from the Sun. Normal lunar phases are not made by Earth shadow. Shadows dominate only when Sun, Earth and Moon are nearly aligned and the lunar orbital nodes also line up, producing eclipses.
Controlled by viewing geometry: roughly half of the Moon remains sunlit, while Earth sees a changing fraction of that illuminated hemisphere.
Controlled by shadow: near new Moon the Moon shadow can reach Earth; near full Moon the Moon can enter Earth shadow. The orbital tilt is why this does not happen every month.
Moonlight is reflected sunlight, but the photograph depends on phase, lunar altitude, azimuth, atmosphere and foreground reflectance together. Use the model to understand direction first, then meter the real scene.
For a moonlit landscape, try ISO 400–1600, f/2–f/4 and roughly 2–15 s on a tripod, then adjust for phase, altitude, focal length and star trailing. If the bright lunar disk is in frame, its exposure may differ radically from the foreground, so bracket when needed.
Phase tells you how much illuminated lunar surface faces Earth; altitude and azimuth tell you where that light enters the composition. A low Moon can create long directional shadows, while a high Moon usually gives shorter, flatter relief.
Check sky and foreground histograms separately when possible. Thin cloud can spread moonlight across the sky and erase faint-star contrast. White balance is a rendering choice; physically, moonlight remains sunlight reflected by the lunar surface.
A total lunar eclipse can be far dimmer than a normal full Moon, and brightness changes throughout the event. Do not carry a bright-Moon exposure unchanged into totality; re-meter and watch motion blur as shutter time grows.
Ordinary phases are not Earth’s shadow, the Moon is not a mirror, and eclipse shadow geometry is a special alignment rather than the cause of the monthly phase cycle. Also do not assume moonlight is negligible for faint-sky work.
Plan lunar direction · Understand phase & moonrise · Test exposure · Check dynamic range
Compare a low bright Moon, a high bright Moon and eclipse totality. Before changing any camera setting, predict shadow direction, sky contrast and whether the lunar disk or foreground will set the exposure limit; then compare that prediction with the model.
Reflected moonlight, ordinary phase geometry and eclipse alignment follow NASA Moon references. NASA Moon Phases · NASA Eclipses and the Moon
The model explains directions, lit fractions and eclipse shadows; it does not predict scene luminance. Exposure ranges in the photography section are starting points only and do not model atmospheric extinction, cloud, lunar albedo variation or foreground reflectance.
True physical scale uses mean radii and mean distances: Sun radius ≈ 109.2 Earth radii, Moon radius ≈ 0.273; Earth–Moon distance ≈ 60.336 and Earth–Sun distance ≈ 23,481. Teaching scale compresses distances so all three bodies fit together.
True mode: Earth radius = 1 · Moon ≈ 0.273 · Sun ≈ 109.2 · Earth–Moon ≈ 60.336 · Earth–Sun ≈ 23,481.
