Pollution

    Hundreds of years ago, life was much harder than it is today. People didn't have modern machines. There was no modern medicine, either.

    Life today has brought new problems. One of the biggest is pollution （污染）. Water pollution has made our rivers and lakes dirty. It kills our fish and polluted our drinking water. Noise pollution makes us talk louder and become angry more easily. Air pollution is the most serious kind of pollution. It's bad to all living things in the world.

    Cars, planes and factories all pollute our air every day. Sometimes the polluted air is so thick that it is like a quilt over a city. This kind of quilt is called smog（烟雾）.

    Many countries are making rules to fight pollution. Factories must now clean their water before it is thrown away, they mustn't blow dirty smoke into the air.

    We need to do many other things. We can put waste things in the dustbin and not throw it on the ground. We can go to work by bus or with our friends in the same car. If there are fewer people driving, there will be less pollution.

    Rules are not enough. Every person must help to fight pollution.

    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?

    As our closest neighbor in space, the moon has been the subject of popular legends, songs and poems since ancient times. And it also attracts scientists deeply.

    But even after centuries of research, many questions remain to be answered about the Earth's only satellite.

    Perhaps the Chang'e-4 lunar probe will be able to find out more of its secrets. On Dec 8, 2018 the probe lifted off from Xichang Satellite Launch Center in Sichuan province. It is the first probe to the far side of moon in human history.

    The Earth's gravity slows the moon's rotation, matching it to the speed of its orbit. Thus, the far side of the moon is always dark and has never been seen.

    It's this sense of the unknown that makes the far side of the moon such an interesting place for scientific and space exploration. Long exposed to solar winds, the far side may have the special soil and minerals in its upper mantle.

    For this reason, Chang'e-4 will study the effect of solar winds on the lunar surface and any minerals found beneath the probe. Chang'e-4 is also carrying flower seeds and potato and silkworm eggs to see whether life is possible on the moon. If it is, then the moon will become a more likely destination for space travel in the future.

    However, because of communication problems, exploring the dark side will not be easy. As the far side is blocked off from us, radio noise coming off Earth is also blocked. This is why China launched the relay satellite Queqiao in May, 2018, so that communication between Earth and the probe could go ahead.

    Power supply is also a challenge to the mission. Chang'e-4 gets energy from the sun through its solar panels. However, a lunar day has the length of 28 Earth days. It means that the probe will need to orbit the moon for over 20 days to be in a position to be able to land in moon daylight and so use its solar panels.

    According to Xinhua, theChang'e-4 lunarprobe landed on the far side of the moon on Jan 3, 2019 successfully, and everything goes well.

    The New York Times described the journey as "groundbreaking", and wrote that it would "give clues to the history and development of the moon".

    Art, as we know, is subjective. What one person considers a priceless masterpiece others might see as nothing more than a giant black square. But there's one very specific kind of painting that almost everyone sees the same way-the kind with the" "strange" eyes that seem to follow you around the room. So what causes this optical illusion (视觉错觉) and how do artists achieve this effect?

    It turns out, for even a moderately skilled artist, this effect isn't a difficult thing to achieve, In fact, the artists need to use a little illusion of depth, making the person depicted on the canvas appears somewhat 3D on a 2D canvas, and to adjust .the gaze (凝视) of the eyes so that they would be looking at someone standing right in front of the picture.

    So what exactly is going on here in our brains that then makes it seem like the eyes follow you even if you move away from being front and center? As demonstrated by a team of researchers from Ohio State University, as you move to the side, the "near? and "far" points of the 2D image don't really change. These near and far points are defined as visible points that, if the image was 3D, would appear nearest and furthest away from the viewer at a given angle.

    The idea is simple. No matter what angle you look at a paining from, the painting itself doesn't change. You're looking at a flat surface. The key is that the near points and far points of the picture remained the same no matter the angle the picture was viewed from. When observing real surfaces in the natural environment the near and far points vary when we change viewing direction. When we observe a picture on the wall, the visual information that defines near and far points is unaffected by viewing direction. Still, we willingly accept and interpret the thing in the painting as if it were a real object.

    Thus, because the perspective, shadows, and light on the painting don't change as you move around, if the eyes in the painting would be staring directly at the observer who is standing in front of the painting, it creates something of an optical illusion in your brain so that the eyes will continue to seem to stare at you as you move to the side.

    In contrast to the eyes following you trick, if the artist tweaks the painting a bit, for example the artist adjusts the gaze of the eyes so that the eyes are looking off somewhere else instead of directly looking at a potential observer, no matter where you stand, the eyes will never seem to be looking at you.

    The technique first began popularly showing up in art around the 14th century when the artist and architect Fillipo Brunelleshi introduced the art world to the idea of "linear perspective", being painting with the idea of everything in the picture converging (聚集) on a specific point on the horizon, creating the illusion of depth. Linear perspective, combined with skilled use of light and shadow, allows artists to create masterfully realistic paintings, including sometimes of people that stare at you creepily no matter where you stand.

    Every day there is less and less space on Earth for rubbish. Yet every day we make more and more rubbish. What can we do? We can recycle some of our rubbish. Recycling means that the rubbish will be made into something that can be used again.

    Recycling helps Earth. And it saves space in rubbish dumps. Half of everything that we put into landfills could be recycled instead. In fact, most things made of paper, metal, glass and plastic can be recycled.

    Paper can be broken into small pieces and made into new paper. Steel and aluminum cans(金属雄)can be melted down(熔化)and made into new cans. The same is true of glass bottles. This can be done over and over again. Recycling doesn't take as much energy as making these things the first time. So we can use less of Earth's fuel resources.

    Plastic can be melted down, too. Then it can be formed into park benches, playgrounds and so on. Some people call plastic the "wood" of the future. Things made of plastic will last about 400 years-even if they stay outside in the weather. No wood can do that!