Why is a "pink moon" so called?

A "Pink Moon" refers to a full moon in April. The name does not derive from the colour of the Moon but from traditional Native American names for full moons.

According to the Maine Farmer’s Almanac – which first published the Native American names for the full Moons in the 1930s – the name “Pink Moon” is derived from one of the first flowers to bloom in spring; the wild ground phlox, which also went by the name “moss pink.” The first full moon of April – which also goes by names such as Sprouting Grass Moon, Egg Moon or Fish Moon – is traditionally a sign of both springtime and Easter.

While Pink Moons are not pink, they can appear to change colour very slightly, if viewed from an extreme northern location. The Moon orbits around the Earth in almost exactly same plane as the Earth orbits around the Sun. That means that when the Sun appears highest in the sky near the summer solstice in June, the full Moon opposite the Sun is generally at its lowest in the sky. In places like northern Norway and Finland this means the full Moon shines through more atmosphere than at other times of the year, which can sometimes give it a slight tint.