A longer path through air removes more blue light
When the Moon is near the horizon, its light travels through much more of Earth’s atmosphere than when it is overhead. Molecules and small particles scatter shorter blue and violet wavelengths more efficiently. The direct light that remains is weighted toward yellow, orange, and red.
The same basic scattering process colors sunrise and sunset. The Moon reflects sunlight, so its light is filtered in a similar way on the final path to your eyes.
Why the color varies
A clean atmosphere may produce a pale yellow Moon. Dust, sea salt, humidity, urban aerosols, wildfire smoke, or pollution can deepen the color and reduce brightness. Thin clouds can add halos or diffuse the disk. Conditions differ with direction and altitude, so two observers in the same region may see different color.
This ordinary horizon reddening is not a blood moon. A blood moon is caused by Earth’s atmosphere filtering light into the planet’s shadow during a total lunar eclipse. An orange moonrise needs no eclipse.
When the Moon becomes white again
As the Moon climbs, the atmospheric path shortens. Less blue light is scattered away, and the disk usually becomes brighter and more neutral. Cameras may record a different color from your eyes because automatic white balance attempts to remove warm tones. Locking white balance helps preserve a sequence that shows the real change.
