Whenever the sun goes down, when we look at the night sky above our heads, although the number of stars in the sky is very dazzling, the entire night sky looks black.

And even if we turn on the flashlight to shine in space, the light of the flashlight cannot penetrate the night sky. The situation we see is that there seems to be some mysterious power in the night sky. Once there is a light source approaching, it can devour the light.

Night has always been a dangerous "synonym". In the original period, at night, there may be a beast that may be hidden around. In an environment without light, the fear of human beings almost draws to the highest point. For humans, the most fearful thing is the unknown thing.

Working during the day and resting at night is the habit of humanity since ancient times. Because at night, the sky was completely dark, and many activities could not be carried out. Because of the lack of scientific cognition, many people in ancient times thought it was created by God at night.

Until the 16th century, with the advancement of science and technology and the development of people's cognition, there were many theories about celestial movement. At this time, people understood why day and night appeared.

If someone asks, "Why is it black at night?" Most people's answers may be: the rotation of the earth has caused day and night to change. Because the earth itself is a planet that is neither glowing nor transparent, it revolves around the sun while rotating around the rotation axis.

Later, with the enhancement of human observation ability, many stars were discovered in the universe. In the 19th century, Oberth, a German astronomer, came to the conclusion that the universe was a uniform and infinite model, and that although stars tended to dim somewhat because of their distance, in fact, all the stars added up to make Earth's night as bright as its day, known as "bright night."

The light from these objects can also light up the night sky. Why is it still so dark? This is known as the Oberth Paradox.

In the Milky Way alone, there are more than 400 billion stars, many of them dozens or even millions of times the mass or brightness of the Sun. Therefore, the sun is very small in the universe, so why is it that only the sun lights up the Earth? Is it a matter of distance?

Some scientists think the reason we can't see all the starlight is that the universe is awash in dark matter and dark energy. These substances cannot be seen with the eye, and they are abundant. According to scientists, dark matter may make up more than 60 percent of all matter in the universe.

Other scientists believe that the universe is uneven, so some places in the universe look dark, while others seem to be bright. The earth is just on the dark side.

There is no accurate answer to this question for the time being. Perhaps we can discover more cosmic mysteries by waiting for the future or human technology.