Scientists have long believed that there is a black hole in the center of our galaxy(星系), the Milky Way. But last Thursday, scientists released the first image(画像) ever of this black hole. The scientists hope the image will help them learn more about black holes and how they work.

All the stars you see in the night sky are part of our galaxy. And in the center of our galaxy is a black hole. It’s called Sagittarius (人马座) A.

A black hole is a place where matter is so dense that the pull of its gravity(引力) is very, very strong. The gravity from a black hole is so strong that even light cannot get away from it.

The scientists actually take a picture of its shadow and the ring of light around the hole called the “event horizon(视界)”. It’s between the hole and the light that is beyond the pull of the hole’s gravity.

The scientists responsible for the picture of the black hole are part of a group called the Event Horizon Telescope project. About 300 scientists in 20 countries have been working on the project for over 12 years.

The telescope the scientists use isn’t really a telescope, but several large radio telescopes around the world. This allows the scientists to later use computers to process the radio signals from the telescopes into a single image.

Sagittarius A is much closer than many other black holes in space, since it’s in our own galaxy. However, it’s changing very rapidly. One scientist described getting a good image of it as “like trying to take a clear picture of a dog quickly chasing its tail”.

The information for the picture of Sagittarius A was collected at the same time. But it took far longer to process the information to create the new image.

Now the scientists have successfully captured the image!

Is there intelligent (有智力的) life on other planets? For years, scientists said “no” or “we don’t know”. But today this is changing. Seth Shostak and Alexandra Barnett are astronomers (天文学家). They believe intelligent life exists (存在) somewhere in the universe. They also think we will soon contact these beings(人；生物).

Why do Shostak and Barnett think intelligent life exists on other planets? The first reason is time. Scientists believe the universe is about 12 billion years old. “This is long enough for other planets to have intelligent life,” say Shostak and Barnett. The second reason is size—the universe is huge. “Tools like the Hubble Telescope (哈勃望远镜) have shown that there are at least 100 billion galaxies,” says Shostak. “And our galaxy, the Milky Way, has at least 100 billion stars. Some planets going around these stars might be similar to Earth.”

In the past, it was hard to look for signs of intelligent life in the universe. But now, powerful telescopes(高倍望远镜) allow scientists to discover smaller planets. These planets might have intelligent life.

Have beings from space already visited Earth? “Probably not,” says Shostak. However, intelligent beings may contact us in other way, such as radio signals (信号). In fact, they may be trying to communicate with us now, but we don’t have the right tools to receive their messages. However, this is changing. By 2025, we could make contact with other life forms in our universe and we might help each other.

From far out in space, Earth looks like a blue ball. Since water covers three-fourths of the Earth’s surface, blue is the color we see most. The continents（陆地）look brown, like small islands floating in the huge, blue sea. White clouds cover around the Earth like a light blanket（毯子）. The Earth is shaped like a sphere, or a ball. It is 25, 000 miles around! It would take more than a year to walk around the whole planet. A spaceship can fly around the widest part of the sphere in only 90 minutes.

Even though spaceships have traveled to the Moon, people cannot visit the Moon without special suits. The Moon has no air or water. Plants and animals can’t live there either. Astronauts first landed on the Moon in 1969. After that, there were six more trips to the Moon. They brought back Moon rocks, which scientists are still studying. There are holes, or craters（火山口）, all over the Moon’ s surface. Scientists believe that meteorites（陨石）smashed into the Moon millions of years ago and formed the craters.

The Sun is the closest star to Earth. A star is a hot ball of burning gas. The Sun looks very big because it is so close. But the Sun is just a medium-sized star. Billions of far-away stars are much bigger than our Sun. The burning gases from the Sun are so hot that they warm the Earth from 93 million miles away! Even though the Sun is always shining, the night here on Earth is dark. That's because the Earth rotates, or turns around, every 24 hours. During the day, the Earth faces the Sun. Then we see light. During the night, the Earth turns away from the Sun. Then it faces the darkness of space.

Each day we learn more about the Earth, the Moon and the Sun.