(CBS SF) — Skywatchers are in for a rare treat this Friday as a Blue Moon takes center stage for a show that happens once every three years.

The saying “once in a Blue Moon,” may hold true for describing uncommon occurrences, but not for depicting the true color of the moon.

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The moon will actually appear gray or silver like any other moon, but its unique timing is what sets this one apart.

The Earth typically experiences 12 full moons, one each month, during most years. This year is an exception with a 13th full moon squeezing into the end of July. These “extra” lunar displays are called Blue Moons.

Two full moons in one month happen about every three years, according to the National Oceanic and Atmospheric Administration.

So where did it get its name? An article written in the 1930’s titled “Once in a Blue Moon” misinterpreted a Farmers Almanac definition of the phenomenon. The term stuck and became a part of popular culture that scientists still use today.

The last Blue Moon was in August 2012 and the next one will return January 2018.

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The Delta Aquarid meteor shower is also taking place this week with the peak expected sometime around July 27-30.

But with the full moon lighting up the night sky, you may have to work extra hard to catch a “shooting star.”

NASA suggests getting as far away from urban light pollution to find a location with a clear view of the night sky.

Here’s where NASA suggests you can view the meteor shower in your area.

Nicole Jones is a digital producer for CBS San Francisco. Follow her musings @nicjonestweets

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