If you look up at the night sky from a busy city street, you'll see a few stars shining brightly. Do the same thing in the countryside or from a mountaintop, and you'll see a lot more of them. Just how many stars are there in space? You could try counting them yourself if you want, but it's probably a better idea to ask the experts at the European Space Agency (ESA). It has come up with its own estimates (估计) on the number of stars in our universe (宇宙).
According to the ESA, there could be as many as 1022 to 1024 stars in the universe. However, this is only an estimate. Remember that Albert Einstein's Theory of Relativity tells that time is not continuous. So experts might be counting stars and galaxies (星系) that disappeared a long time ago.
This number includes stars that are much larger than our sun, and others that are much smaller. It considers trillions (万亿) of galaxies that are spread out across our universe. Some of these galaxies are considered to be Dwarf Galaxies because they have as few as 10 million stars. Others are Giant Galaxies because they have more than a trillion stars.
The ESA estimate also includes the Milky Way, and it is our home galaxy. According to ESA scientists, it is made up of at least 100 billion stars. In fact, our sun is a medium-sized star in it. It is a member of the white cloud of stars which can sometimes be seen across a moonless night sky.
Many stars have planets around them. In fact, some scientists believe that there are as many planets as stars out there. Perhaps there is life on these planets, just waiting to be discovered. If that's it, maybe there are a few alien scientists who can give us an exact answer about the number of stars in the universe.
