Transparent animals let light pass through their bodies the same way light passes through a window. These animals typically live between 

the surface of the ocean and a depth of about 3,300 feet—as far as most light can reach. Most of them are extremely delicate and can be 

damaged by a simple touch. Sonke  Johnsen, a scientist in biology, says, “These animals live through their life alone. They never

touch anything unless they're eating it, or unless something is eating them.”

And they are as clear as glass. How does an animal become see-through? It's trickier than you might think.

      The objects around you are visible because they interact with light. Light typically travels in a straight line. But some materials slow and

 scatter(散射) light, bouncing it away from its original path. Others absorb light, stopping it dead in its tracks. Both scattering and absorption

 make an object look different from other objects around it, so you can see it easily.

But a transparent object doesn't absorb or scatter light, at least not very much, Light can pass through it without bending or stopping.

That means a transparent object doesn't look very different from the surrounding air or water. You don't see it —you see the things

behind it.

   To become transparent, an animal needs to keep its body from absorbing or scattering light. Living materials can stop light because they

contain pigments(色素) that absorb specific colors of light. But a transparent animal doesn't have pigments, so its tissues won't absorb

 light. According to  Johnsen, avoiding absorption is actually easy. The real challenge is preventing light from scattering.

Animals are built of many different materials—skin, fat, and more—and light moves through each at a different speed. Every time light

moves into a material with a new speed, it bends and scatters.Transparent animals use different tricks to fight scattering. Some animals are

simply very small or extremely flat. Without much tissue to scatter light, it is easier to be see--through. Others build a large, clear mass of

 non-living jelly-lie(果冻状的)material and spread themselves over it .

    Larger transparent animals have the biggest challenge, because they have to make all the different tissues in their bodies slow down light 

exactly as much as water does. They need to look uniform. But how they're doing it is still unknown. One thing is clear for these larger animals, staying transparent is an active process. When they die, they turn a non-transparent milky white.

    Life may have evolved on at least three planets within a newly discovered solar system 39 light years from Earth. Astronomers at the NASA have discovered no less than seven roughly Earth-sized worlds orbiting a dwarf star in the system. Scientists had previously identified a tiny number of "exoplanets", which are believed to have the qualities needed to support life. However, the new system contains an unprecedented(前所未有) number of Earth-sized, probably rocky planets, and is being acknowledged as an "accelerated leap forward" in the search for extraterrestrial (外星球的)life.

    Three of the new planets are said to be particularly promising because there might exist oceans. Thomas Zurbuchen, associate administrator of NASA, told a press conference in Washington: "This gives us a hint that finding a second Earth is not a matter of 'if', but 'when'."

    The planets were discovered using NASA's Spitzer Space Telescope, which was able to track how fast each of the planets crossed the star Trappist-l and completed an orbit. From this the research team calculated how far the planets were from their star, and therefore how likely they are to be habitable.

    NASA's Hubble Space Telescope is already being used to search for atmospheres around the planets. Future telescopes, including the proposed European Extremely Large Telescope and the James Webb Space Telescope, may be powerful enough to discover markers of life, such as oxygen in the atmospheres of exoplanets.

    Astronomers believe there could be as many as 40 billion potentially habitable worlds in our galaxy, the Milky Way. Prof Zurbuchen said that now was a "gold-rush phase" in the search for these exoplanets.

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    We may be only three weeks into December, but artist Jonnie Hartman has been in the holiday spirit for months, designing and building the Grand America Holiday Window Stroll.

The goal with each window stroll is to create playful and uplifting displays (展示), according to Hartman. "I really try to do something lighthearted, something whimsical, that is, something everyone can connect with and maybe not see every day in the real world," Hartman said.

    She designs all of the window displays by hand, starting with pencil sketches, then illustrating the designs on her computer and sending parts of the drawings to be printed. From there, Hartman works with a team of five people to build the displays, creating, sewing and embellishing (润色) many elements by hand.

    However, a challenge Hartman has faced over the years as she has designed the displays is making sure all of the measurements are right for elements to fit inside the windows.

"When I was in college, I was an art major, and I thought, 'I don't need math. I will never use it. I'm an artist,' and guess what, it's the most important thing that I use, ''Hartman said. "If I don't get that right, then the windows don't fit, the pieces don't come together and it just doesn't work out."

    The holiday window stroll gives Hartman a unique opportunity to hear feedback from those who observe her creations, which is something she doesn't always get to experience with her other artworks. She said it's fun to hear people's reactions as they go through the holiday window stroll.

"It just makes me happy that I can kind of set the tone for people's holiday season and just maybe bring a smile to their face," Hartman said.

    Do you want to live another 100 years or more? Some experts say that scientific advances will one day enable humans to last tens of years beyond what is now seen as the natural limit of the human life span.

    "I think we are knocking at the door of immortality(永生)," said Michael Zey, a Montclair State University business professor and author of two books on the future. "I think by 2075 we will see it and that' s a conservative estimate(保守的估计)."

    At the conference in San Francisco, Donald Louria, a professor at New Jersey Medical School in Newark said advances in using genes as well as nanotechnology(纳米技术) make it likely that humans will live in the future beyond what has been possible in the past. "There is a great effort so that people can live from 120 to 180 years," he said. "Some have suggested that there is no limit and that people could live to 200 or 300 or 500 years."

    However, many scientists who specialize in aging are doubtful about it and say the human body is just not designed to last past about 120 years. Even with healthier lifestyles and less disease, they say failure of the brain and organs will finally lead all humans to death.

    Scientists also differ on what kind of life the super aged might live. "It remains to be seen if you pass 120, you know; could you be healthy enough to have good quality of life?" said Leonard Poon, director of the University of Georgia Gerontology Centre. "At present people who could get to that point are not in good health at all."

    People from East Asia tend to have more difficulty than those from Europe in distinguishing facial expressions — and a new report published online in Current Biology explains why.

    Rachael Jack from University of Glasgow, said that rather than scanning evenly across a face as Westerners do, Easterners fix their attention on the eyes.

    "We show that Easterners and Westerners look at different face features to read facial expressions," Jack said. "Westerners look at the eyes and the mouth in equal measure, while Easterners favor the eyes and ignore the mouth."

    According to Jack and his colleagues, the discovery shows that communication of human emotions is more complex than previously believed. As a result, facial expressions that had been considered universally recognizable cannot be used reliably to convey emotions in cross­cultural situations.

    The researchers studied cultural differences in the recognition of facial expressions by recording the facial movements of 13 Western people and 13 Eastern people while they observed pictures of expressive faces and put them into categories: happy, sad, surprised, fearful, disgusted, or angry. They compared how accurately participants read those facial expressions using their particular eye movement strategies.

    It turned out that Easterners focused much greater attention on the eyes and made significantly more errors than Westerners did. "The cultural difference in eye movements that they show is probably a reflection of cultural difference in facial expressions," Jack said. "Our data suggests that while Westerners use the whole face to convey emotions, Easterners use the eyes more and the mouth less."

    In short, the data shows that facial expressions are not universal signals of human emotions. From here on, examining how cultural factors have diversified these basic social skills will help our understanding of human emotions. Otherwise, when it comes to communicating emotions across cultures, Easterners and Westerners will find themselves lost in translation.

    When I was small and my grandmother died, I couldn't understand why I had no tears. But that night when my dad tried to cheer me up, my laugh turned into crying.

    So it came as no surprise to learn that researchers believe crying and laughing come from the same part of the brain. Just as laughing has many health advantages, scientists are discovering that so, too, does crying.

    Whatever it takes for us to reduce pressure is important to our emotional health, and crying seems to work well. One study found that 85 percent of women and 73 percent of men report feeling better after crying.

    Besides, tears attract help from other people. Researchers agree that when we cry, people around us become kinder and friendlier and they are more ready to provide support and comfort. Tears also enable us to understand our emotions better; sometimes we don't even know we're very sad until we cry. We learn about our emotions through crying, and then we can deal with them.

    Just as crying can be healthy, not crying - holding back tears of anger, pain or suffering - can be bad for physical health, Studies have shown that too much control of emotions can lead to high blood pressure, heart problems and some other illnesses. If you have a health problem, doctors will certainly not ask you to cry. But when you feel like crying, don't fight it. It's a natural –and healthy-emotional response.