Have you seen Avatar（《阿凡达》）? It's a popular 3D movie, and you may have to wear 3D glasses to see it. The 3D glasses make the images(图像)from the movie look as if they were coming straight towards you. 

More and more 3D movies are coming to theaters. Some say that 3D TV sets will come into our homes in the near future. 3D technology can make TV and movies are more exciting. However, people with eye problems may get headaches if they spend too much time watching 3D movies. Why?

      When we look at an object(物体), each eye sees it at a different angle(角度). Our eyes send the two images to our brain(大脑), and the brain puts them together. 3D technology uses two film projectors(投影机). One projects a left-eye-image and the other projects a right-eye-image. 3D glasses allow us to see a different image in each eye. So, when we are watching a 3D movie, our brain can't put together the images sent to our eyes. The brain needs to work harder at “reading” the images. That makes it easier for people with eye problems to get dizzy(头晕的) or have headaches. A famous eye doctor said if your eyes can't focus(聚焦) on the same object at once, you will have trouble watching 3D movies.

    Stop reading for a minute and think about what you see when you look up at the sky on a clear night. You probably see many stars (星星). Long long ago, farmers watch some stars to know when to plant their crops. Travelers did so to find their way in the dark. Today stars are still important to some people.

    Scientists find that most stars are very big. In fact some stars are so far away that it would take millions of years to get to them even by spaceship.

    Another thing we know today about stars is that some are made up of(由…组成) hot gases. The gases are so hot that they send out light. If you watch a star carefully, you may notice that it twinkles(闪烁)sometimes. As you may understand, light from a star must shine through the air before you can see the star. Air is always moving, it makes light from the star move back and forth. When the light moves, it makes the star twinkle. Stars also have different colors. The colors of a star depend on how hot it is. To our surprise, the cool stars are red and the hottest stars are white.

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    Different weather makes people feel different.It has an effect on health，intelligence(智力) and feelings.

    In August，it is very hot and wet in the southern part of the United States.People there have heart trouble and other kinds of health problems during this month.In the Northeast and the Middle West，it is very hot at some times and very cold at other times.People in these states have more heart trouble after the weather changes in February or March.

    The weather can also influence intelligence.For example，in a 1983 report by scientists, the IQ(智商) of a group of students was very high when a very strong wind came，but after the strong wind，their IQ was 10% lower.The wind can help people have higher intelligence.Very hot weather，on the other hand，can make it lower.Students in many schools of the United States often get worse in exams in the hot months of the year(July and August)．

    Weather also has a strong influence (影响)on people's feelings.Winter may be a bad time for thin people.They usually feel cold during these months.They might feel unhappy during cold weather.But fat people may have a hard time in hot summer.At about 18℃，people feel more comfortable.

    Are you feeling sad，tired，or unhappy today？It may be the weather's problem.

    Many people may sometimes wish it could be summer all year round. However, as nice as summer is, we really need the other seasons as well.

    Then why do we have different seasons? We know that the Earth spins on its own axis (轴线). This makes day and night. In 24 hours the Earth turns round once. When we are facing the sun, it is day. When we face away, it is night. Simple!

    We travel around the sun in a circle. So why does it get colder in winter and hotter in summer? It's because the axis of the Earth is tilted (倾斜的). It means that in summer some places, such as the UK, are leaning towards the ssun. The temperature rises. As the Earth travels around the sun, these places begin to tilt away and the temperature drops. It becomes winter.

    This is why when the UK has winter, Australia has summer. Imagine having Christmas dinner on the beach! But not all countries have seasons. Countries near the equator (赤道), the line which goes round the middle of the Earth, don't have different seasons. The weather stays almost the same temperature all the year round. Can you think why this is? The middle doesn't tilt very much, does it? This means the seasons don't change much.

    Then what about the North and South Pole? What are the seasons like there? Because they get very far away from the Sun, their seasons are very extreme. There are only two seasons near the North and South Pole: winter and summer. What's more, they only have one sunrise and one sunset a year. It is dark for six months of the year and light for six months of the year. What problems would there be if you had to live somewhere that was dark for six months of the year and light for six months of the year?

    "Life is speeding up. Everyone is getting unwell."

    This may sound like something someone would say today. But in fact, an unknown person who lived in Rome in AD 53 wrote it.

    We all love new inventions. They are exciting, amazing and can even change our lives.

    But have all these developments really improved the quality of our lives?

    Picture this: You're rushing to finish your homework on the computer. Your mobile phone rings, a QQ message from your friend appears on the screen, and the noise from the television is getting louder and louder. Suddenly the computer goes blank and you lose all your work. Now you have to stay up all night to get it done. How calm and happy do you feel?

    Inventions have speeded up our lives so much that they often leave us feeling stressed and tired. Why do you think people who live far away from noisy cities, who have no telephones, no cars, not even any electricity(电) often seem to be happier? Perhaps because they lead simple lives.

    Our family in the UK went "back in time" to see what life was like without all the inventions we have today. The grandparents, with their daughter, and grandsons Benjamin, 10 and Thomas, 7, spent nine weeks in a 1940s house. They had no washing machine, microwave, computer or mobile phones.

    The grandmother, Lyn, said, "It was hard physically, but not mentally." She believed life was less materialistic(物质的). "The more things you have, the more difficult life becomes," she said. The boys said they fought less. Probably, they said, because there was less to fight over, such as their computer. Also Lyn changed from being a "fashionable, beer-drinking granny, to one who cooked things."

    Here are some simple ways to beat the stress often caused by our inventions!

    Don't be available all the time. Turn off your mobile phone at certain times of the day.

    Don't check your emails every day.

    Don't reply to somebody as soon as they leave a text message just because you can. It may be fun at first, but it soon gets boring.

    Make sure you spend some time talking to your family. Set aside one evening a week when you don't turn on the television. Play cards and chat instead.

    Get a low technology hobby. Every day, do something in the old way, such as walking to have a face-to-face meeting instead of using the email or telephone.

    Don't worry too much about life—laugh more.