There will be a full moon in the skies over the Chicago area this week, but it is a rare spectacle that brings two unique events together on one night.
According to scientists at NASA, the full moon will be a super blue moon, and will be the first in a series of so-called “Supermoons” in coming months.
So what makes this moon so interesting and special? Here’s a breakdown.
What is a “Supermoon”?
A “supermoon” is a full or new moon that occurs when the moon is within 90% of its closest distance to the Earth. The closer proximity of the moon to Earth makes for somewhat bigger and brighter full moons, according to astronomers.
According to NASA, this will mark the first of four consecutive “supermoons,” with September and October both occurring when the moon is even closer in its orbit of the Earth.
What is a “blue moon”?
Most Americans know a “blue moon” is the second full moon within a calendar month, but that definition is actually much newer than the original meaning of the phrase, according to NASA.
The original definition of a “blue moon” was the third full moon in a season that has four total full moons, according to NASA. There will be a total of four full moons during astronomical summer, with the final one taking to the skies in September.
Most Americans also know that a “blue moon” usually isn’t blue in hue.
Just how rare is a “Super Blue Moon”?
Given that there are differences in definition of both a supermoon (based on how close the moon is to Earth) and a blue moon (whether referring to two full moons in a month or the third full moon of a four-full moon season), it’s tricky to mathematically express just how rare a “Super Blue Moon” is.
However, according to USA Today, by the definitions being used by NASA for this week’s event, it can roughly be estimated that a “super blue moon” of this type will only occur once every 10 years on average, though the gap can be substantially longer than that.
The gap between “super blue moons” won’t be quite so wide this time. According to “Full Moon,” there will be seasonal blue moons on May 20, 2027 and Dec. 20, 2029, but the next seasonal “Super Blue Moon” will occur on Sept. 19, 2032.