Outer space is a place where there are many exists. Despite having many stars, we often see in various photos of astronauts that the outer space looks very dark. In fact, as we know, dark are usually indicates the absence of light. While stars are objects that able produce light independently.
The question that arises then is why the outer space is very dark?
Although it seems simple, this question has been contemplated by many scientists for centuries, such as Johannes Kepler and Edmond Halley whom already had many contributions to astronomy.
Quoting from one of the sites owned by the US Space Agency (NASA), starchild.gsfc.nasa.gov, to make it easier to understand the reasons why the universe looks dark, we should divide this question into two things.
First, about the difference in color of the sky on earth and in space. Second, dark colors that occur even though there are many stars in space.
To answer the first question, it must be understood that blue in the sky occurs because light hits molecules in the earth’s atmosphere and spreads in all directions. The blue color during the day occurs from the results of the light scattering process.
Well, when on the moon or the International Space Station (ISS) no atmospheric molecules was “hit” by sunlight. As a result, we will cannot see blue sky as we seen on earth.
Then, the more difficult question is why even though many space stars remain dark? A German astronomer named Heinrich Wilhelm Olbers made a theory to explain this phenomenon in 1823. At present, the theory is called the Olbers Paradox.
Olbers explained that the universe had unlimited age, but had an age of 15 billion years. This means that we can only see objects as far as the distance of light that can be taken in only 15 billion years.
As a result, starlight farther away from it cannot reach us so that it will not make outer space fully bright.
In the short version, we cannot see stars in the entire universe. That’s because many starlights are not enough to reach our current location.
With only certain stars and the distance is quite far, while the universe is very wide, the color of outer space becomes dark.
Another reason is the theory of motion of light
Geza Gyuk, Director of Astronomy at Adler Planetarium and researchers at the University of Chicago, said that light usually moves straight forward in a line unless it bounces off something or is bent by a lens.
“So, even though space might be full of light, nothing makes way to our eyes except when we see something bright,” Gyuk said. “Because most of the universe is empty, outer space appears dark,” he added.