Why can the Hunter’s Moon look orange as it rises?

Moonlight is sunlight reflected by gray lunar rock, so it carries every color. On its way to you, it meets air molecules. They scatter short wavelengths, like blue, far more than long ones, like red.

When the Moon is high, its light crosses a thin slice of atmosphere, and plenty of blue gets through. Near the horizon, the path runs almost sideways through the air. By the air-mass formula Sunset Lab uses, it is up to about 38 times longer. Much of the blue is scattered away. What is left looks yellow, orange or red.

NASA explains the longer path near the horizon, and dust or smoke can deepen the effect. Photographs by Emma Pezzi on USRA’s Earth Science Picture of the Day show it well: the same Moon, in different colors at different heights.

We have no Moon color model, but Sunset Lab shows the same scattering with the Sun. Sunlight and moonlight lose their blue the same way.

1. 1 See

   Tap Noon · 60°. Most of every color gets through, so the light stays nearly white.

2. 2 Change

   Now tap Sunset · 0°. The air crossed jumps to about 31 times the overhead path.

3. 3 Understand

   Almost none of the blue is left, while about a tenth of the red still arrives. Picture that beam as moonlight.

Sunset Lab models clean air, so its colors are illustrative, not a forecast. On a clear evening near full Moon, compare the Moon at moonrise with an hour or two later.

A full Moon sits opposite the Sun in our sky. So as the Sun sets in the west, the full Moon rises in the east. It is near the horizon in the evening, when many people look up and its light crosses the most air.

Moon Phase Lab shows the geometry. Sunlight always lights half the Moon, and a full Moon is when that half faces us. It answers why the Moon is full, not why it looks orange. NASA’s phase guide covers the same idea.

The name comes from the calendar, not from optics. In the Northern Hemisphere tradition, the Harvest Moon is the full Moon closest to the September equinox. The Hunter’s Moon is the full Moon after it. Nothing about its light is special. Any full Moon can look orange near the horizon, and a high Hunter’s Moon looks as pale as any other.

No. Phases come from viewing angle, not Earth’s shadow. A lunar eclipse happens only when a full Moon also passes through Earth’s shadow, which its tilted orbit usually avoids. Then the only sunlight reaching the Moon has crossed Earth’s atmosphere. That light has lost much of its blue on the way, so the Moon can glow coppery red. NASA’s eclipse guide explains the geometry.