Blue Supermoon seen over Vicksburg

Published 1:24 pm Thursday, August 31, 2023

The full moon Vicksburgers experienced Wednesday night was a rare Blue Supermoon.

Why is this Blue Supermoon rare?

This special event is the coincidence of two uncommon moon traits: A supermoon, which occurs when the moon appears larger than usual, and a blue moon, or the second full moon in a month. According to NASA, a blue moon only occurs once every two or three years on average and a blue moon that is also a supermoon is even rarer. While a “super blue moon” can occasionally happen twice within two months, at other times, it could be 20 years before the phenomenon repeats. On average, such an event occurs once per decade, per the agency.

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Why do we have Supermoons?

Astronomy lovers get to experience supermoons because the moon’s orbit around Earth isn’t a perfect circle. As a result, the distance between Earth and the moon varies as it loops around the planet. Roughly three or four times each year, the full moon occurs while the moon is at its closest point to Earth, called the perigee. These supermoons appear 7 percent larger than the average full moon and 14 percent larger than a full moon at its most distant point from Earth, or the apogee.

What is the meaning of the title Blue Moon?
Every 29.53 days, the moon undergoes a complete phase cycle, transitioning from a bright full moon to a dark new moon — and back to a full moon again. Since 29.53 days is relatively close to the lengths of the months in the calendar, most months only have one full moon. But because the calendar is based on the Earth’s motion around the sun, not the phases of the moon, the periods don’t match up exactly. As a result, two full moons are sometimes squeezed into one month. (February, with only 28 or 29 days, can never have a blue moon.) In the early 1900s, in places such as the Maine Farmers’ Almanac, the term “blue moon” was used to refer to a related phenomenon — when four full moons occurred within a given season, instead of the typical three. In these cases, the third full moon was known as “blue.”

What is the rarity of Blue Moons?
While Wednesday’s “super blue moon” will appear large, those expecting to see it glow with an unusual blue color will be disappointed. During a “blue moon,” the lunar surface won’t change its hue but viewers can still appreciate its rarity. The last blue moon happened in August 2021, and after the one this month, a blue moon won’t return again until May 2026.

If anyone missed seeing the rare Blue Supermoon Wednesday night, don’t fret. Even though it might be starting its waning gibbous phase, it will still look almost as large Thursday night as Wednesday night.

Information for this article was gleaned from The Smithsonian Magazine online and from NASA.