Have you ever heard someone use the phrase"once in a blue moon"？People use this expression to describe something that they do not do very often．For example，someone might say that he tries to avoid eating sweets because they are unhealthy，but will eat chocolate"once in a blue moon"．Or someone who does not usually like to go to the beach might say"I visit the shore once in a blue moon．"While many people use this phrase，not everyone knows the meaning behind it．

    The first thing to know is that the moon itself is never really blue．This is just an expression．In fact，the phrase"blue moon"has to do with the shape of the moon，not the color．

    As the moon travels around the earth，it appears to change shape．We connect names with certain shapes of the moon．For example，when we can see a small part of the moon，it is called a crescent moon．A crescent is a shape that looks like the tip of a fingernail（指甲尖）．When we cannot see the moon at all，it is called a new moon．When we can see the whole moon，it is called a full moon．Usually，there is only one full moon every month．Sometimes，however，there are two full moons in one month．When this happens，the second full moon is called"a blue moon"．

    Over the next 20years，there will only be 15blue moons．So you can seldom see a blue moon． This fact has led people to use the expression"once in a blue moon"to describe things they don't often do in their lives．

    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?

    Inventions usually make a big difference to people's lives. Do you have any great inventions at home? Do they help you a lot in your life or bring you much fun? Here are some of the most useful inventions in families according to a survey.

    Some researchers explain how most people form their social groups with people of their age. Especially, as children and teenagers, even adults, people make their friends based on proximity (邻近) more than anything else. Even in a college classroom, the students may not make friends with those who have similar personalities and interests. It's the people they really sit next to. Clearly, who stands to you has the greatest influence on you. As Jim Rohn has widely said. "You are average (平均) of five people you spend the most little with."

    Over the past ten months, I've paid Ryan, it Famous writer of several bestselling books, to help with the book I'm writing. Working with him has shown me just how low my standards for my work are. For example, every time I send him a drab (草稿), he shows me how it could     be 10 times better, and he holds me to that standard.

      ▲   It's because that I don't know what I don't know. Working with Ryan has made me realize what is possible and what it takes to create something powerful.

    Like Ryan, my business partner Richard has wonderful ideas and far different experience than I have. He has written 36 New York Times Bestsellers. He's been speaking and doing events for 20 years. Richard always performs at high levels, and he is also very strict with me because my performance is a reflection (反映) on him. It's not a bad thing because it creates high pressure (压力) to help me make great progress in organizing author training.

    In a word, you need to stay with those people who can help you realize your level and potential. Staying with people who have higher standards is the fastest way for you to change. If you don't change your environment, your progress will be very slow. Who you stay with has huge importance. You can't ignore this.

    Have you ever been ill? When you are ill, your body becomes hot, and there are pains all over your body. You must be unhappy because of it. You don't want to work. You stay in bed feeling sad.

    What makes us ill? It's germs. Germs are everywhere. They are very small and you can't find them with your eyes, but you can see them with a microscope (显微镜). They are very, very small and there could be hundreds of them on a very small thing.

    Germs are always found in dirty water. When we look at dirty water under the microscope, we can see them in it. So your father and mother will not let you drink dirty water.

    Germs aren't found only in water. They are found in the air and dust (灰尘). If you cut your finger, and if some of the dust from the floor goes into the cut, some of the germs will go into your finger. Your finger will become big and red, and you will have much pain in it. Sometimes the germs will go into all of your body, and you will have pain everywhere.