High above Earth， more than a hundred weather satellites （卫星） are collecting information． They send pictures of cloud patterns to scientists on Earth． They also take measurements （测量） of weather conditions， such as air temperature， air pollution and lightning strikes． The meteorologists study the pictures． They make mathematical models using the measurements． The models can help meteorologists make forecasts． The models forecast how， when and where the weather will change in a few hours or in several days． They might forecast （预测） rain in your area tomorrow． If so， you might decide to take your umbrella to school．

More important， weather forecasts tell when bad weather is on the way． Floods， tornadoes， thunderstorms， and hurricanes put people in danger． Weather forecast can save lives． For example， satellites pictures taken over time show how fast a hurricane is growing and the path it is taking． People can be ready for the storm． Meteorologists are always working to make better forecasts．

The United States began using weather satellites in 1960． Today's satellites take clearer pictures and collect more information． Satellites collect information about cloud systems． They have a bird's-eye view of smoke from wildfires and of ash clouds from volcanoes （火山）． Weather satellites can also follow an oil spill on the ocean's flow． They can watch a cloud of sand blowing from a desert in Africa． Information from weather satellites is sent to supercomputers． These computers are huge， and they make mathematical models quickly．

Planes and ships need to know the weather so they can go around dangerous storms． A weather satellite can also help a ship in trouble． The satellite is part of a search and rescue （救援） system． The satellites can send a warning from the ship in danger to the U．S． Coast Guard． The Coast Guard can send out a rescue team．

The question whether there is life on Mars (火星) has made the public think a lot for more than a century. The closest look showed Mars to be a dusty, cold world, covered by air too thin to breathe. A British spaceship and Europe’s Mars spaceship plan to land on Mars or enter orbit (轨道) around it. One of the NASA’s (美国宇航局) spaceships is expected to land on January 3, the other is going to land on the opposite side of Mars on January 24.

Since 1960, over twenty spaceships sent to Mars have failed. Most have been lost on flying up or landing because those are the most difficult times of any flights.

Scientists wanted to find out whether there was water in Mars. In October, a team of scientists reported that Mars had been a dry wasteland. But weeks later, a second team reported differently that they had found some marks showed clearly that they were made by the rivers. Such marks told us that Mars was a warmer place billions of years ago—just as life first appeared here on Earth. Scientists at once raise a question: if what they said is true, what happened on Mars? Then what about the earth?

I’m a virus (病毒) for the common cold. It has been a long time since I infected (感染) humans last time. Today I tried to infect a boy in a primary school all day.

His name is Sam, I waited on his desktop, and when he touched the desk I jumped on his finger. Unluckily, Sam didn’t touch his eyes, mouth or nose. Then, right after class, he washed his hands. Now I’ m full of soap and sitting in a sink (水槽)!

Tuesday, January 22nd

This morning I jumped into the nose of Sam’s best friend, Bill. Unluckily, the mucus (粘液) in his nose caught me. I thought it was over for me, when suddenly Bill sneezed while he was talking to Sam.

I knew that would send me right into Sam’s face! However, Sam quickly gave Bill a tissue (纸巾), and Bill sneezed into that instead! Infecting people is harder than I imagined.

Wednesday January 23rd

I’m feeling very unhappy today. Some scientists caught my friend Harry and put him under a microscope. Harry is a flu virus and he’s a dangerous little guy. Besides, Sam ate all his vegetables today. He’s exercising, and he’s getting eight hours of sleep every night. His body is too strong for me!

Thursday, January 24th

I tried to infect Sam again today, but he washed his hands five times and never touched his face! He also gave tissues to every student in his class who was sneezing. It’s impossible to give him a cold! So I have to give up and I’m moving to another school.