People who love Star Wars movies do not need a reason to leave a photograph or message on social media.

On any given day, you might see Star Wars-related photos all over Facebook and Twitter. There might be a cat made to look like Darth Vader or a dog in what appears to be the clothing of a storm trooper.

Anytime a Star Wars video comes out online, people watch it. Look at the trailer for the next Star Wars movie, "Rogue One." It came out in April. Just a month later, it has over 35 million views on YouTube.

Star Wars fans do not need a reason to celebrate. But every year they have a special day, anyway.

And that day is May 4!

Do you know why?

Perhaps the most famous saying from all of the Star Wars movies is "May the Force Be With You."

On May 4, people have fun saying "May the Fourth Be With You."

The two sayings sound nearly the same.

That is why May 4 is known as "Star Wars Day." And the hashtag #MayThe4thBeWithYou is trending on Twitter. By Wednesday afternoon, that hashtag was used almost 600,000 times.

Many businesses hoping to promote their products used the hashtag. Volkswagen posted a photo of one of its famous VW buses as one of the AT-AT walkers from the 1980 film "The Empire Strikes Back."

Stars Wars Day leads to all sorts of visual humor. Sports teams use photo editing software to make it look as if their players were in the movies. Perhaps a tennis player or golfer holds a light saber instead of a racquet or golf club.

And that's What's Trending Today.

I'm Anna Matteo. May the Force Be With You.

Dan Friedell wrote this story for Learning English. George Grow was the editor.