The Smallest Life Around Us

    Tiny plants and animals live all around us．We cannot see them because they are so small，but they are everywhere. They live in the soil，in the air，and in rivers and oceans．They grow on mountains and in caves．Some live in the ice at the north and south poles; some live where it is very hot．They are found throughout cities and in the country. They grow on other plants and animals．Some are even living on you，on your skin，hair，and inside your body，in your mouth，nose，and all through your body．

    These tiny plants and animals are called microbes．The word microbe is made from two other words：micro，meaning small，and bios，meaning life．So，microbe means small life．

    Microbes have been on earth for a very long time．They may have been the first forms of life to be alive．Today there are more microbes in the world than all other living things．

    People did not know microbes had existed（存在） long．They were too small for them to see．But people did see many changes in their world﹣important changes．And they did not know what caused them．They saw food that they kept too long change color and begin to smell bad．They saw cuts and wounds grow red and painful and become worse. They saw old plants and leaves and trees crumble apart on the forest floor and disappear into the soil．Such changes were a natural part of the world，but people did not understand them．They did not know these changes were evidence(证据) of tiny plants and animals growing all around them.

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    No Car Day was first started by 34 cities in France on September 22, 1998. It was started to protect the environment. By now, more than 1,000 cities around the world have had a No Car Day.

    The first No Car Day in China was in Chengdu in 2001. Other cities including Taipei, Shanghai and Wuhan, also support the day.

    In Beijing, more and more people are taking part in the activity. It asks drivers to leave their cars at home for one day each month and walk or ride a bike to work. It also calls on Beijingers not to use cars on June 5th (World Environment Day). The slogan for the day is, "If we drive for one less day, we can have one more nice day."

    So far, more than 200,000 drivers have shown their support. "We can't control the weather, but we can choose not to drive," said Wu Zhonghua, a car club chairman. Beijing is trying to have 238 blue sky days this year. In the first quarter of 2007, Beijing only had 52 blue sky days. This was 11 days less than the number for the same period last year. Much of the dust comes from the desert, but cars cause most of the air pollution. We must do more for No Car Day.

    Twinkle, Twinkle Little Star is a lovely song for children, but it has two misunderstandings (误解). First, stars aren't little. Some may be Earth-sized, but most are bigger than Jupiter, the largest planet in the solar system (太阳系). Second, they don't twinkle; they shine. And the brightness and color of the light from each star provide information about its temperature, size and even its age. viewing the stars from Earth is a bit like looking at them through a water filter (过滤器) because the air is thick compared to the emptiness of space. What is more, air is always moving, so starlight appears to be moving, too. The air also makes stars appear dimmer (暗淡的) than they would be if we could see them from space.

    If you stop and look at the sky carefully on a dark and moonless night, it's easy to find color differences among stars. The color of a star is a signal of its surface temperature. The hottest stars are blue, and the next hottest are white. Yellow stars like the sun are next, while red stars are the coolest of the visible (可见的) stars. Many red stars are so dim that people can't see them at all, and some stars hardly send out any light at all. One reason that stars different in brightness is that hotter stars produce more energy than cooler ones, but another important reason is that some are much bigger than others.

Some stars appear brighter to humans simply because they're closer. Astronomers rank (排列) the brightness of stars which are seen from Earth by giving them a name known as magnitude (光度) —the smaller the magnitude, the brighter the object. They have also designed a number that ranks stars according to how bright they are when compared to each other. With a magnitude of minus 26.7, the sun is the brightest object in the sky.

    In some science fiction movies, evil robots refuse to die, no matter how hard people fight back.

    Now science fiction has become science fact. For the first time, scientists have made a robot that can take a beating (挨打) and keep on going. Scientists from Cornell University made the robot, which looks like a spider with four legs.

    Until now, even the most advanced (先进的) robot was almost certain to break down when it was damaged. That is because its computer inside simply doesn't know how to make the machine work after its shape has changed.

    To deal with this problem, the scientists put eight motors (发动机) and two sensors (传感器) that read how the machine is working. They all give signals to the machine's software. Using this information, the computer can then figure out the machine's shape at any moment.

    The new technology is a big advance in robot-making, scientists say, and it's far from scary. It may someday help scientists create better artificial (假的) arms and legs and give new freedom to people who lose them. It might also help scientists understand how people and animals figure out their own sense of place in space.

    "It has been difficult to design robots that can work well when the environment changes or when it's damaged," says Olaf Sporns of Indiana University in US. "With this work, we are nearer to solving this problem."