In this scene from the Star Trek episode "The Enemy Within," a transporter malfunction creates an evil Kirk, who proceeds to come aboard the ship.

After the Enterprise crew catch a virus that removes their inhibitions, one crew member rambles angrily about how humans don't belong in space and threatens Sulu with a knife.

In the Star Trek episode "The Enemy Within," the Enterprise crew finally get rid of an evil version of Captain Kirk using the transporter.

Kirk tries to literally slap Spock into helping him save the ship, but Spock, infected with the virus, can only lament about spending a whole lifetime learning to hide his feelings. Suddenly, Kirk also seems to be acting strangely.

Captain Kirk finds himself in Olympus, and face to face with the Greek god, Apollo... or so it would seem! But what might a classical deity want from the stunned and bemused Star Trek crew?

Captain Kirk’s crew has stolen a cloaking device from the Romulans, but when they attempt to hold the Romulan Commander hostage, they find out just how dangerous she is.

A mysterious visitor, Seven, tries to convince Captain Kirk to let him disarm a nuclear missile/warhead that is heading for Earth. With Spock unable to do it himself, the crew is left with no choice but to trust him.

When humanoids with powers to control the ship challenge the order of command, Kirk must maintain his authority and keep them firmly in line, all while calming the nerves of his anxious crew.

Let's find out more about an American activity aimed at school kids: the spelling bee. What is it and how does it work?

Sigrid talks about "The Elementary Spelling Book" by Noah Webster, which was the basis for the American English dictionary and a big part of the development of spelling bees in the United States.

Sigrid explains how a spelling bee normally proceeds. There are fixed rules and there are options.

In recent years, we've seen an increase in the intensity of tropical storms and hurricanes due to global warming. But how and why do hurricanes form? Sigrid provides a basic explanation of this phenomenon.

We continue to explore the phenomenon of hurricanes. Why are they so dangerous? And do they serve any purpose?

Columbus Day has always been a controversial holiday in the United States. In this video, Sigrid goes back in time to get some historical background, which sheds a new light on its significance.

Most Americans don't realize how Columbus Day came to be a national holiday, but it actually doesn't have that much to do with Christopher Columbus, and we might even recognize a connection to present-day events. To recall something Mark Twain once supposedly said, "History doesn't repeat itself, but it often rhymes."