The “Pink Moon” is a popular term for a specific full moon, often leading people to question whether the moon itself displays a rosy hue. This annual event is a recurring fixture in the lunar calendar, with its name rooted in cultural traditions rather than any change in the celestial body’s appearance. Understanding the source of the name and the physics of moonlight clarifies the difference between the cultural label and the visual truth.
The Cultural Origin of the Name
The designation “Pink Moon” is one of many traditional full moon names, popularized by the Old Farmer’s Almanac using Native American conventions. The name is often attributed to the Algonquin tribes of the northeastern United States, who used the full moon to track seasonal changes and agricultural cycles. These names were linked to specific, observable environmental events signaling the changing season.
The Pink Moon name refers to the widespread blooming of the wildflower Phlox subulata in early spring. This plant, commonly known as moss pink or creeping phlox, is native to eastern North America. The flower blankets the ground in a vibrant pink carpet, and its arrival coincided with the full moon occurring in this part of the year.
This naming tradition resulted in the April full moon having several other names reflecting springtime renewal. Other monikers include the Sprouting Grass Moon, the Egg Moon, and the Fish Moon, which marked the time when shad fish began swimming upstream. These alternative names illustrate that the full moon served as a reliable seasonal marker for planting, hunting, and fishing.
The Astronomical Significance
From an astronomical perspective, the Pink Moon is simply the common name for the full moon occurring in April. A full moon phase is reached when the Earth is positioned between the Sun and the Moon, fully illuminating the lunar hemisphere facing Earth. This alignment happens approximately once every 29.5 days, the duration of one complete lunar cycle.
The full moon’s timing also determines the date of Easter in certain religious calendars. In Christianity, the April full moon is designated the Paschal Full Moon, defined as the first full moon on or after the spring equinox. Easter Sunday is then observed on the first Sunday following this Paschal Moon. This highlights how the lunar cycle was integrated into historical timekeeping.
Visual Appearance and Color Misconceptions
Despite its name, the Pink Moon does not appear pink to the naked eye. The moon’s surface is naturally dark gray and white, and its color as seen from Earth is usually a bright, luminous white. Any perception of color—pink, red, orange, or yellow—is a phenomenon of atmospheric physics, not a change in the moon itself.
When the moon is near the horizon, its light travels through a much thicker layer of Earth’s atmosphere. This extended path causes the atmosphere to scatter away shorter wavelengths of light, such as blue and green, via Rayleigh scattering. The longer, warmer wavelengths (red, orange, and yellow) are less scattered and dominate the light reaching our eyes, causing the moon to appear reddish or orange. This effect can happen with any full moon when it is low in the sky.