In the universe, as we all know, there is the sun, the moon, the earth and a good many stars. Through our geography lessons, we know the earth goes around the sun, and the moon goes around the earth. We have day and night because the earth keeps turning all the time. When our part of the earth turns to the sun, it is day. When our part of the earth turns away from the sun, it is night.

    Just because the moon is closer to the earth than the sun, it looks much bigger than the sun. Big things will look smaller when they are further, and small things also look bigger when they are nearer.

    The sun is big enough to give out very strong light. The moon can't give any light at all, but it looks quite bright, too. Why? In fact, the light from the moon comes from the sun. The moon looks much bigger and brighter than the stars. But actually (事实上) the stars are much bigger and brighter than the moon. They look smaller than the moon also because they are further away from the earth.

    There are many other planets in the universe. But of all the planets, only on the earth there are living things and people can only live on the earth, too. But at 9:00 a.m. on October 15th，2003, Chinese pilot Yang Liwei was sent up to space. He stayed there for 21 hours. It was the first time for Chinese to get into space.

     We often read the Air Quality Index （空气质量指标） or AQI reported in the newspaper. The AQI helps us understand what the air quality around us means to our health. The AQI uses colors, numbers and words to tell us about the air. Let's see what these colors and numbers mean.

    When you are on a long road trip or in a traffic jam during a daily-commute ， it may seem harmless to connect your phone to your car's USB port．But unless you really need to use your phone，charging(充电)your iphone during your commute could be a big mistake．

    Why? For starters，the USB port in our car probably provides less electricity than your phone really needs to charge．As a result，your phone might stop working while it charges.

    Many people may notice that on their way home from work their phone charged very little during their 30-60 minute commute，"says Brad Nichols，an engineer at Staymobile．"It is mostly because that the phone is using more power than the car charger isproviding it．"

    Nichols also says that your phone could receive too much power，especially if you are using a cigarette lighter port to charge up．Most cigarette lighters can provide more power than most chargers can afford．If a charger cannot keep providing the proper power, it may make the phone broken．

    Charging your phone could do harm to your car's battery(电池)，too．This usually isn't a big deal for those who own new cars with healthy batteries，Nichols says．But if your car is older，you might not want to charge your phone through its USB port．

    Most importantly，it's not safe to use your phone while driving．"Anytime a person's hands leave the wheel or eyes leave the road，it becomes dangerous for them and the other people around them," Nichols points out．Bottom line：Play it safe，and wait until you get home to charge your phone．

    Teenagers are known for being creative and full of new ideas. Let's have a look at these teenage inventions that might change the world.

    Albert Einstein is right once again! He thought of the idea about gravitational waves years ago with his Theory of Relativity, but scientists are finally discovering that it really exists now. But what are gravitational waves, and why are they important?

    Well, gravitational waves are made by black holes and can change time in space. Black holes aren't holes but are lots of matter put together into a very small area. They are created when a star, much like our sun, explodes and leaves behind this dense* material. It doesn't shine like a star any more, and it becomes black.

    The black holes that made these waves are special. About 1.3 billion years ago, there were two black holes that kept moving closer and closer together. Finally, they hit each other and formed one big black hole. The energy is given off and created the ripples* in space. These ripples are gravitational waves. For example, imagine you throw a stone into a pool. It creates ripples that change the shape of the water. Well, that's kind of what the influence of one black hole hitting the other has in space.

    Gravitational waves are hard to explore. But thanks to the efforts of scientists, the ripples were discovered on Feb. 11th, which is the first time in human history. Einstein was excellent to know this 100 years ago before we have the technology. It can give us a new view of the universe we live in. The discovery of gravitational waves, unlike stars, galaxies and other bright objects, black holes don't produce light, so we can't see them by tools. Gravitational waves allow scientists to look at the universe not only with light, but also with gravity. "Everything else in astronomy like the eye," A scientist told The New York Times. "Finally, astronomy grew ears. We had never ears before."

    Now, we will be able to find black holes and things that are much further away from Earth, which means much more space exploration in the future. And who knows, this discovery could even lead to time travel!