You might want to start your Labor Day Weekend with a little star gazing.

We’re scheduled for a ‘blue’ moon tonight, which actually has nothing to do with the color of the moon and isn’t even that rare, despite the saying “once in a blue moon”.

So where does ‘blue’ moon come from?

According to Space.com:

In 1946, Sky and Telescope magazine traced it to the Maine Farmer’s Almanac, where it referred to the third full moon in a season that contains four full moons instead of the usual three.

However, Sky and Telescope get the definition wrong, describing a “blue moon” as the second full moon in a month with two full moons. The incorrect meaning didn’t became widely used until decades later, and was particularly boosted when the board game Trivial Pursuit used it in 1981.

So, under the now commonly-used definition, we’ll have a blue moon tonight because it’s the second full moon of August, after the first one on August 1st.

As for the rarity of blue moons, they’re actually not that uncommon, taking place on average once every 2.7 years.

So if you miss it tonight, it’ll be back in 2015.