Ask Ellen: What’s a black moon?

Ask Ellen

A generic image of a black moon.

GRAND RAPIDS, Mich. (WOOD) — We’ve all heard the phrase “once in a blue moon,” but have you ever heard of a black moon?

It’s equally rare, and it we technically have one Wednesday night! 

The concept for a black moon is very similar to the one used to define a blue moon, so let’s start there. 

Usually, we only see one full moon each month but because our yearly calendar doesn’t exactly line up with the lunar calendar, we can sometimes see two full moons land in the same month.

When this happens, the second moon of the month is called a blue moon. Its rarity is what gives the saying “once in a blue moon” its strength. 

A blue moon only happens once every two to three years. A black moon is just as infrequent.  

Before we go any further, it is important to know why a full moon and a new moon happen. Both are natural progressions in our lunar cycle and it all has to do with how the sun, moon, and earth are aligned.

The below image from NASA is especially helpful to visualize the cycle:

A full moon happens when the sun’s rays are directly hitting and illuminating the moon. That light then reflects back to planet Earth, making the moon look big and bright. 

A new moon happens when the moon swings in between the earth and the sun. All of the sun’s rays hit the side of the moon facing away from planet Earth, reflecting the light back into outer space.

From our perspective, a new moon looks like a dark shadow in the nighttime sky. New moons happen about once every month — technically about every 29.5 days. 

A new moon already occurred on July 2 of this year. On Wednesday night, we will see a second. Because the moon is the second new moon in the same month, it will be called a black moon.

Other than the fact that we have squeezed two new moons into the same month, there isn’t much special about Wednesday night’s moon. If we want to take the naming game even further, the moon is undergoing a close pass to earth. So, if you wanted to get very technical, we could call tonight’s moon a super black moon. 

Still, names like this are fun to know and can help remind us all to look up, and appreciate the vast beauty, complexity and order that is our universe. 

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