Question: How often do you get to see four full moons in any given season? Answer: Once in a blue moon. Now the only question is, what constitutes a blue moon? A blue moon will be on display tonight through Wednesday morning, so let's look at the history of blue moons.

Though the modern definition of a blue moon describes it as the appearance of two full moons in the same month, that is not entirely accurate. For those who are wondering, a blue moon also has nothing to do with its color.

Rather, the term blue moon came about to describe the third of four full moons in any given season. Since seasons usually only have three full moons, this was quite a rare event. In fact, a true blue moon happens only 7 times every 19 years. 

"[T]his definition actually preceded the more modern definition of a Blue Moon as being the second of two full moons to occur in one calendar month," writes Earth Sky.

What's also interesting to note is that the modern definition of a blue moon occurs with the exact same frequency as the original definition. That is because such a concentration of full moons in any given month inevitably leads to four in a season.

But blue moon history doesn't stop there, skygazers. There was actually a time in human civilization when the moon actually did appear blue. For that, however, we have to go 130 years back in time.

"There was a time, not long ago, when people saw blue moons almost every night. Full moons, half moons, crescent moons - they were all blue, except some nights when they were green," notes NASA's Tony Phillips. "The year was 1883, the year an Indonesian volcano named Krakatoa exploded."

The ash from the volcano's eruption  covered much of the atmosphere, turning the moon blue in the process by acting as a filter for blue light. Similar phenomena have been noted after other major volcano eruptions.

So while the moon won't actually be blue tonight, rest easy knowing that tonight is still a relatively rare event astronomically speaking. If you would like to actually see the moon turn blue, a strong forest fire could create enough ash to do the trick, though it is not recommended that you take such actions.