The name “Pink Moon” refers to April’s full moon, but the celestial body does not glow with a rosy hue. The name is misleading, as the moon’s appearance is consistent with any other full moon throughout the year.
The History Behind the Name
The name “Pink Moon” is not a visual description but a cultural and historical marker tied to the cycles of nature. This designation originates from various Native American traditions, particularly the Algonquin tribes of North America, who named the full moons to mark the passage of seasons and the timing of activities.
The specific reference for the Pink Moon is the moss pink, or creeping phlox (Phlox subulata), a wildflower native to the eastern United States. This plant is one of the earliest and most widespread flowers to bloom, carpeting the ground in vibrant pink in early spring. The full moon in April simply coincides with this springtime bloom, hence its name.
This full moon has also been known by other names that reflect the seasonal changes of early spring, such as the Sprouting Grass Moon, the Egg Moon, or the Fish Moon. These names, like the Pink Moon, served as a communal calendar, indicating the time for activities like planting seeds or when the shad fish began swimming upstream. The custom of using these traditional names was popularized for a general audience by publications like the Old Farmer’s Almanac.
The Actual Visual Appearance
When viewed high in the sky, the Pink Moon presents as a typical full moon, appearing bright white or a pale yellow. Its light is essentially reflected sunlight, which makes the lunar surface appear in shades of gray and white to the naked eye. While the April moon can sometimes be a “supermoon” (closer to Earth, appearing slightly larger and brighter), it is often a “micromoon” (farther away, appearing slightly smaller and dimmer).
However, the moon’s visual color changes significantly when it is low on the horizon, such as just after moonrise or before moonset. In these moments, the moon frequently takes on a golden, amber, or orange color. This color shift is an atmospheric effect and is not unique to the Pink Moon.
The appearance of this warm hue is a function of the moon’s position relative to the observer and the Earth’s atmosphere. Once the moon climbs higher into the night sky, its light passes through less atmospheric interference, causing it to revert to its familiar bright white appearance.
Atmospheric Science and Lunar Hues
Any full moon, including the Pink Moon, appears orange or reddish when near the horizon due to a phenomenon called Rayleigh scattering. This mechanism is the same one that makes sunrises and sunsets appear colorful. When the moon is low, its light must travel through a greater amount of the Earth’s atmosphere to reach the observer.
The atmosphere is filled with tiny molecules of gas that interact with the moonlight. Shorter, high-energy wavelengths of light, such as blue and violet, are scattered away by these particles. This scattering effect removes the blue light from the visual path.
The longer, lower-energy wavelengths, specifically the red and orange light, are less affected by the scattering. Consequently, the moon is left bathed in a warm, reddish glow when it is observed near the horizon. This temporary coloration is a terrestrial effect, not an inherent quality of the lunar surface.