On March 14, math and science lovers around the world celebrated a special day: Pi Day.

Pi is equal (平等的) to about 3.14, but the number is endless. It is sometimes written in Greek. With the help of computers, mathematicians have been able to work pi out to over a trillion (万亿) decimal (小数的) places, but there is still no end to the number. This makes pi confusing, even for the most famous scientists and mathematicians.

Pi Day is celebrated around the world on March 14, since how we write this date, 3/14, looks just like the number pi.

For some people, the attraction of Pi Day goes far beyond math and science. Pi shows up throughout popular culture. You can see it in movies, comics, music and more. “In modern movies, any time the filmmaker wants to evoke (唤起) a sense of mystery, often the symbol pi is used,” said David Blatner, a Jewish-American writer of The Joy of Pi.

People also love trying to memorize the digits (数字) of pi and competing against others to see who can remember the most. Many teachers hold class contests to see how many numbers their students can memorize. The Guinness World Record for reciting (背诵) the most digits of pi is held by Lyu Chao of China, who successfully recited pi out to nearly 67,890 decimal places.

Above all, Pi Day is about having fun with the number. People celebrate Pi Day by eating or throwing pie and with fun pi-related games and activities. In 2016, Princeton, New Jersey, held a birthday party for Albert Einstein whose birthday also falls on March 14. There was also a “Walk a Pi Event” where people walked 3.14 miles together. Just like the number itself, the possibilities for Pi Day are truly endless.

Dr. Chip Taylor teaches biology at a university in the United States. He studies one kind of North American butterfly. During the late summer or autumn, this butterfly travels from Northern USA and Southern Canada to Mexico, covering thousands of miles. Fantastic facts about the butterfly have been drawing Dr. Taylor’s attention.

In Mexico, the butterflies always return to the same small piece of forest, which is only 20 kilometers wide. Here, as many as 230 million butterflies spend the winter. They cover some trees almost completely. The butterflies that return to the south are the great-great grandchildren of the butteries that left for the north. When they begin to travel north in spring, the females lay eggs. They lay eggs on only one plant: milkweed.

But in Mexico, people cut down the trees that the butterflies need to rest on because they want more land for farming. In the United States and Canada, farmers use chemicals that kill milkweed. This worries Dr. Taylor a lot.

Now things are improving. Mexico has begun to protect parts of its forests. The United States and Canada have encouraged farmers to use fewer chemicals.

Scientists still don’t understand how the butterflies know when to fly south. If they are even a few days late, they will freeze (冻僵). And how do all the great-great grandchildren find the same forest in Mexico every year? This is both puzzling and interesting for many scientists.

There are many mysteries yet to be discovered by those interested in science. Would you like to study biology?

Are you bored with your daily life? Here are some things you should try before you are 18, because after that it’s too late.

Learn to swim

Seriously, this is so important that it can save your life. lf you can’t swim well, you won’t be able to do water sports like water skiing, surfing and diving. Even taking a boat trip will be dangerous for you. Make sure you do it.

Try at least one kind of team sports

Being a good team player is an important skill in life. You can’t just think of yourself, but have to work well with other people. Other advantages of team sports like basketball, football and baseball are that they keep you fit and healthy, and they are also great fun. Teams usually have a good social life too—you’ll go to lots of parties and make many friends.

Collect something

One of the best hobbies for under-18s is collecting things. You can collect different kinds of stamps, or you can collect things that make you remember what you have done, just like cinema tickets for films you have seen or emails from friends. The best way to collect is to have a special album to put your collection in and to write what each thing means to you. That way you won’t forget.