There are actually many planets that are outside of our solar system. The first of these far-off planets was discovered in 1988. So far, astronomers have found more than 3,500 such planets, and they think there are a lot more. Astronomers have found many of them using a special space telescope. This telescope can see very far into space. Many of these planets go around their own star, like our planet goes around the sun. A few of these planets even go around two stars. However, some of these planets are by themselves and do not go around a star. Astronomers cannot see these planets with their eyes. Instead, they use some special methods to find out where the planets are and what they are like.

Even though these planets are very far away from us, we know some things about the planets. We know that they come in all kinds of colors and sizes. Some of the planets appear to be red or blue, and they can be much bigger than Jupiter (木星). Some of these planets also seem to be made of the same kinds of things as can be found on Earth. A number of the far-off planets seem to be completely solid and made of rocks, they are hotter than Jupiter, too.

While far-off planets are interesting, there is an important reason why astronomers are looking at them. Astronomers want to find a planet like Earth. They think that there may be some out there that have air and water like Earth. Such planets, astronomers believe, may also support life on them. That would certainly be something to find! So astronomers keep searching. Who knows what they will find out there?

It can be hard to believe that it is just an illusion (错觉) when the moon has a “changing” size, but it is true. You can actually test it yourself and even catch it with a camera.

People mainly notice the moon looking bigger when it is full and near the horizon (地平线). 【小题1】 Imagine you are standing outside close to your house. Your house will look big, and if the moon rises next to it, the moon will look normal. If you look at a house from far away, though, the house looks very small.

【小题2】 However, the things—a house, a mountain or anything else—that are compared with the moon have “changing” sizes. They look bigger or smaller depending on how far away from them you are. 【小题3】

There are several explanations that sounds reasonable but wrong for the moon illusion. 【小题4】 The moon’s orbit is not perfectly round, so the moon does get nearer and farther away over the course of a month.

It’s easy to test the moon, illusion, and you can do it yourself. Next time you see the moon looking bigger than usual, bold out your hand with a straight arm. 【小题5】 Wait a little while until the moon moves higher into the sky and try the experiment again. The moon may look smaller, but your same finger will over it just the same.

Mars is a neighboring planet in our solar system. Scientists study Mars because it could hold clues that could help us learn more about life on Earth. For decades, scientists have used robot technology to better understand Mars. In December 2020, scientists introduced a group of robots named Mars Dogs at a yearly meeting.

The Mars Dog is a four-legged robot created by the company Boston Dynamics. It, along with other similar robots, can move around in ways the wheeled rovers (探测器) that explored the planet never could. Traditional Mars rovers are limited mostly to flat surfaces. However, many scientifically interesting Martian regions are only reachable by crossing very rough (崎岖的) ground or going below ground. Walking Mars Dogs are well-suited for such challenges—even if they fall down, they can get back up again. These robots can also explore underground by walking around rocks and lowering themselves into caves. They are even capable of selecting which path to take. While they do this, they collect measurements to build a map of what they see.

A Mars Dog would also be about 12 times lighter than present rovers. It would be able to travel much faster, reaching normal walking speeds of 5 kilometers per hour during tests. Compare that to the Curiosity rover that is presently exploring Mars. Curiosity rolls along the Martian surface at about 0.14 kilometers per hour.

Before going to Mars, the team members are testing the robot. They even take the robot to outdoor locations similar to Martian landscapes. Those tests show that the robots, without any help, can walk around rocks and map deep caves. “These behaviors could one day enable significant scientific missions to take place on the Martian surface and subsurface,” the scientists said at the yearly meeting.