No, mom, the moon won't glow green for the first time in 420 years. It's weed day | Miami Herald

Some people may be seeing green on Friday night, but it probably won't be the moon they're looking at.

Rumors have been swirling through Facebook and other social media that a very rare alignment of planets — which only happens once every 420 years — will cause the moon to glow green for 90 minutes.

The astronomy site EarthSky.org reported that "green moon" was the most searched-for term on its site over the last few weeks, and searches across the web have been shooting skyward since March.

Such a fascinating celestial event would be something to see — if it were actually happening.

Unfortunately, there will be no green moon Friday night. The hoax can be traced back all the way to 2016, when people first began sharing it as a joke about April 20, or 'Weed Day.'

Snopes sniffed out the original post, which didn't actually mention April 20 at all and instead suggested Uranus would reflect its light onto the moon in May. The site tracked the joke's spread across the web after people began replacing the the original (fake) reasoning with the new weed-centric joke.

The number 420 has long been associated with marijuana, and so April 20 (4/20) has become a kind of informal holiday for pot enthusiasts.

To those familiar with the connection, the joke was fairly clear. But a lot of Twitter users say their uninitiated parents (or grandparents) are falling for the hoax — and they're the ones having to break the bad news.

But that doesn't actually mean a green moon is impossible. One actually was reported about 135 years ago, according to NASA — but it was caused by the drifting plumes of ash from a violent volcanic eruption, not a rare planetary alignment.