March 21 is World Sleep Day. Here are some facts about sleep.
Sleep at advised times
In 2021, the Ministry of Education（MOE）advised that junior and senior high school students should go to bed before 10 pm and 11 pm respectively（分别的）.
How do astronauts sleep?
Just like on Earth, a person in space goes to bed at night and then wakes up the next day. But in space there is no up or down, and you do not feel the pull of gravity（重力）. As a result, astronauts usually sleep in fixed sleeping bags.
Earworms happen while sleeping
Some people enjoy listening to music a lot. While we' re awake, the music we know well keeps ringing in our ears, which is called earworms（耳虫现象）. This can happen during sleep as well, which could cause problems in getting to sleep and staying asleep.
Sleep with your pet?
Pets, like dogs and cats, do not sleep continuously and they will often get up and walk on the bed, which can make you sleep even worse.
But recent studies found that having pets in the bed may help people who are often worried. The pets, like soft toys, can help cut down their worry.
Socks can help us sleep
Studies have shown that wearing socks to bed can help you fall asleep faster!
Hands and feet help exchange（交换）heat between the far ends of the body and the heart. Wearing socks means an increase of blood to your hands and feet, which cuts down your core（核心的）body temperature. The lower the core body temperature is, the faster you fall asleep.
