On Sunday, April 22, people all over the world take time out to appreciate (珍惜) the earth that we all share. It’s Earth Day, a special day to learn about our planet (星球) and how to take care of it.
On Earth Day, some people listen to speeches about the environment. Others help clean up their offices or save water and electricity at home. Your parents may even decide to take a day off from driving their cars.
The idea for Earth Day came from a US Senator (参议员), who was worried about pollution and the health of plants and animals. And the idea quickly caught on (流行起来). In 1970, the first Earth Day was celebrated. More than 20 million people in cities all over the U. S.  took part. Since then, Earth Day has been used to educate people about their role in taking care of our planet.
Now Earth Day has become a global celebration. In 1990, 200 million people from 140 countries took part in clean-ups, tree planting and other environmental events on Earth Day.
根据短文内容，回答下列问题。
When is Earth Day? ___________________________
Who came up with the idea for Earth Day? _______________________
How many people celebrated the first Earth Day in 1970? ________________________
Is Earth Day popular around the world now? _________________________
What is Earth Day?  ____________________________