The term “Super Blue Moon” describes a single astronomical event combining two distinct concepts related to the Moon’s appearance and timing. This convergence can be confusing, as it involves orbital mechanics and a calendrical definition. Understanding the visual outcome requires separating the two components: the “Blue Moon” and the “Supermoon.” This article clarifies the visual effect of this rare full moon.
Deconstructing the Blue Moon
The “Blue Moon” designation is a naming convention based on timing, having nothing to do with the Moon’s actual color. One common definition is the occurrence of the second full moon within a single calendar month. Since the lunar cycle is approximately 29.5 days long, a full moon appearing early in the month allows for a second full moon to occur. This happens roughly once every two to three years.
A separate, older definition refers to the third full moon in an astronomical season that contains four full moons. Seasons typically have only three full moons, so the appearance of a fourth requires naming the third one a Blue Moon.
Understanding the Supermoon
The “Supermoon” relates to the Moon’s distance from Earth, which directly impacts its apparent size and brightness. The Moon’s orbit is an ellipse, meaning the distance varies throughout the month. The closest point in the orbit is called perigee, and the farthest point is apogee.
A Supermoon occurs when a full moon aligns closely with perigee. This proximity makes the Moon appear noticeably larger and brighter than an average full moon. A Supermoon can appear up to 14% larger and approximately 30% brighter than a full moon occurring at apogee, sometimes called a micromoon.
The Combined Visual Effect
A Super Blue Moon is the coincidence of these two phenomena: a full moon that is the second in a month (or third in a season) and is also near its perigee. The most common misconception is that the Moon will actually appear blue in color due to the name. The Moon will not look blue, but will instead maintain its typical silvery-grey or white coloration.
The Moon can only temporarily appear blue under extremely unusual atmospheric conditions. This happens when fine particles, such as those from a massive volcanic eruption or large wildfire smoke, scatter red light effectively. This scattering allows blue light to pass through to the observer.
Without such atmospheric interference, the Super Blue Moon’s appearance is defined entirely by the Supermoon component. It will look distinctly larger and more luminous than a typical full moon, especially when observed near the horizon. While the size difference of 14% may be subtle to the casual observer, the combined effect of increased size and 30% greater brightness makes it a striking sight. The Super Blue Moon is a rare event, as the timing of the “Blue Moon” definition must align with the Moon’s closest orbital approach. Observers will be treated to one of the most brilliant full moons of the year.