Is there anybody out there? For centuries humans have wondered although the ways in which we have gone about this have varied. As we have gained a greater understanding of the universe, our searches have taken on more concrete(具体的) forms. Questions about aliens(外星人) have become a subject for science rather than science fiction.

Now new cooperation between the Very Large Array (VLA) observatory in New Mexico and the SETI Institute in California means that our curiosity about whether aliens exist can be closer than ever before to being satisfied. Data from the VLA’S 28 radio telescopes, used to scan a vast area of sky, will be fed through a special supercomputer that will search for distant signals.

How likely it is that a signal will be found, and what this might mean, are hard questions to answer. SETI’s existing projects have not discovered any signals from other planets so far. But recent discoveries in space and Earth sciences have provided some encouragement for those who are enthusiastic about the possibility, however remote, of detecting other civilizations.

Once it was thought that our solar system could be unique. Since the discovery of the first exoplanet (a planet beyond the solar system) in the 1990s, thousands more have been located. Around one in five stars is now thought to have a planet in their orbit(运行轨道) in a so-called “habitable(适合居住的) zone”—that is, at a distance from the star where the temperature means that life is theoretically possible.

Are Earth’s 7.5 billion humans, along with billions of other animals and plants they share their home with, on their own in the universe? If there is another life form somewhere, could it be as intelligent as humans? Or could it threaten them? I think all of these need further exploration. As explorations of Mars continue, and a new set of observations from the James Webb Space Telescope are set to begin, our interest in the possibility of alien life appears as much as before.

A satellite is an object in space that orbits around another. It has two kinds — natural satellites and artificial satellites. The moon is a natural satellite that moves around the earth while artificial satellites are those made by man.

Despite their widespread impact on daily life, artificial satellites mainly depend on different complicated makeups. On the outside, they may look like a wheel, equipped with solar panels or sails. Inside, the satellites contain mission-specific scientific instruments, which include whatever tools the satellites need to perform their work. Among them, high-resolution cameras and communication electronics are typical ones. Besides, the part that carries the load and holds all the parts together is called the bus.

Artificial satellites operate in a systematic way just like humans. Computers function as the satellite’s brain, which receive information, interpret it, and send messages back to the earth. Advanced digital cameras serve as the satellite’s eyes. Sensors are other important parts that not only recognize light, heat, and gases, but also record changes in what is being observed. Radios on the satellite send information back to the earth. Solar panels provide electrical power for the computers and other equipment, as well as the power to move the satellite forward.

Artificial satellites use gravity to stay in their orbits. Earth’s gravity pulls everything toward the center of the planet. To stay in the earth’s orbit, the speed of a satellite must adjust to the tiniest changes in the pull of gravity. The satellite’s speed works against earth’s gravity just enough so that it doesn’t go speeding into space or falling back to the earth.

Rockets carry satellites to different types and heights of orbits, based on the tasks they need to perform. Satellites closer to the earth are in low-earth orbit, which can be 200-500 miles high. The closer to the earth, the stronger the gravity is. Therefore, these satellites must travel at about 17,000 miles per hour to keep from falling back to the earth, while higher-orbiting satellites can travel more slowly.

How many things can you see in the night sky? A lot! On a clear night you might see the Moon, some planets, and thousands of sparkling stars.

You can see even more with a telescope. And with bigger and bigger telescopes you can see more and more objects in the sky. And you can see those objects in more and more detail.

But scientists believe there are some things in the sky that we will never see. We won't see them with the biggest telescope in the world, on the clearest night of the year.

That's because they're invisible. They're the mysterious dead stars called black holes.

You might find it hard to imagine that stars die. After all, our Sun is a star. Year after year we see it up in the sky, burning brightly, giving us heat and light. The Sun certainly doesn't seem to be getting old or weak. But stars do burn out and die after billions of years.

As a star's gases burn, they give off light and heat. But when the gas runs out, the star stops burning and begins to die.

As the star cools, the outer layers of the star pull in toward the center. The star squashes into a smaller and smaller ball. If the star was very small, the star ends up as a cold, dark ball called a black dwarf. If the star was very big, it keeps squashing inward until it's packed together tighter than anything in the universe.

Imagine if the Earth were crushed until it was the size of a tiny marble. That's how tightly this dead star, a black hole, is packed. What pulls the star in toward its center with such power? It's the same force that pulls you down when you jump—the force called gravity. A black hole is so tightly packed that its gravity sucks in everything—even light. The light from a black hole can never come back to your eyes. That's why you see nothing but blackness.

So next time you stare up at the night sky, remember: there's more in the Sky than we can see! Scattered in the silent darkness are black holes—the great mystery of space.