Space has no end. It stretches on and on to infinity. The human mind cannot comprehend infinity, but you can try to imagine. Imagine flying in a spaceship to outer space at the speed of light. You will never reach an end. This is how the “universe” is: totally “unlimited”.
Space itself is blackness, except those parts illuminated by the stars suspended in space. The sun is really a star, but it is a special star because it is the star closest to our earth. The sun is the star which provides all the light and heat energy needed to sustain life on earth. All the other stars in the universe are too far away to provide any significant light or heat energy for earth. However, they do provide a small amount of light in the night.
The earth where we live is an example of a planet. There are nine planets which revolve around the sun at different distances. The planets vary in size. Giant pieces of rocks sometimes revolve around each planet. These rocks are caught within the gravitational pulls of the earth and the sun, so they keep revolving around the earth, unable to break free. These rocks which revolve around planets are called “natural satellites”.
The earth only has one natural satellite. It is called the “moon”. Sometimes, at night, when you see the moon “shining” brightly, it is really “reflecting” light from the sun. The sun is a ball of flaming gas. It produces an enormous amount of heat and light. On the other hand, the moon is just a cold rock. It cannot produce heat or light. It just reflects it, and appears to shine.
Some of the planets which revolve around the sun has not just one, but several natural satellites.
The sun, all the planets which go around the sun, and all the moons which go around the planets together make up the “solar system”. The word “solar” means “having to do with the sun”.
But our solar system is just one example of billions upon billions of “solar systems” which exist in the universe. Since the universe has no end, there is no end to the number of solar systems out there. In other words, the number of systems like our solar system in the universe is “infinite”.
Take a peek out your window on a starry night and wonder what’s there. Each star you see may very well have its own set of planets revolving around it. And who knows if there are other living creatures on those planets, looking at our sun, and thinking of it as a twinkling star.
Related: Why do stars twinkle?