This is What's Trending Today:

"Happy Halloween" is the Number One trending topic on Twitter today.

That is because October 31 is Halloween and people in the United States and elsewhere are excited to celebrate.

Each year on the last day of October, children and adults celebrate the holiday by dressing in cute, frightening or humorous costumes. Young people carry out the Trick-or-Treat tradition to get candy from neighbors.

People also cut faces or designs into pumpkins and light them from inside.

Many people hold Halloween costume parties.

In fact, many Americans were celebrating Halloween all weekend long. The NBA champion Cleveland Cavaliers had a costume party. LeBron James dressed as a character from a 1990s television show.

Even family animals are included. At an event in Boston, one dog came dressed as a Lobster sandwich.

Some costumes are popular every year. Since Halloween honors the dead, people often dress as ghosts or zombies.

Many children like to dress as imaginary characters. Cinderella, Superman, Catwoman, Captain America and Wonder Woman are popular.

But many adults like to represent a person who has been in the news.

For example, many dressed as presidential candidates Hillary Clinton and Donald Trump.

Others chose Ken Bone, the man from Illinois who gained brief fame after he asked a question during the second presidential debate.

Others like to dress as their favorite celebrities or characters from movies and television shows.

The hosts of a popular morning television program dressed like characters from the 1990s. They looked like actor Jerry Seinfeld, singer Baby Spice, former First Lady Barbara Bush and characters from the movie Pulp Fiction.

The singer Usher even posted a photo showing scary-looking doughnuts.

But this year, some scientists made Halloween an educational holiday as well.

The U.S. space agency NASA posted a video explaining a recently discovered kind of star called a "pumpkin star."

And that's What's Trending Today.

I'm Alice Bryant.

Dan Friedell wrote this story for Learning English. Caty Weaver was the editor.