Why is space dark even though it is full of stars?

According to the predictions of many astronomers, There are likely to be many sextillion stars in the observable universe, yet space remains almost completely dark and lightless. After all, with so many bright stars in different regions, wouldn’t it be normal for these stars to illuminate space, leaving it with a little less darkness?

This issue is not a simple one and has already been discussed among the leading scientists on the subject, and this is exactly how the Olbers Paradox emerged. The theory was developed by German astronomer Heinrich Wilhelm Matthias Olber in the mid-19th century. In summary, Olbers explains that the sky remains dark for a simple reason: Because the universe is not infinite. – at least from what we’ve looked at so far.

As we can see from the Earth’s surface each night, the night sky offers the greatest feature of space: an endless darkness with tiny bright spots of distant stars, planets and galaxies. But if you are an astronaut and on a space mission, the sky looks even darker and scarier.

TecMundo gathered information from astronomers and experts in the field to better explain why space is dark and even full of stars. Check out!

Why is space dark?

When the German astronomer observed the night sky in the mid-19th century, he wondered why the universe was not extremely bright if there were billions of stars in space. So he began to study the finitude of the universe and concluded that the lack of light in space was due to the universe not being infinite; otherwise the night sky would be filled with an infinite number of stars, causing great illumination at every vantage point.

“If the universe were infinitely large and infinitely old, we would expect the night sky to be bright because of the light from all those stars. Every direction you look in space, you are looking at a star. But we know from experience that space is dark! This paradox is known as the Olbers Paradox,” explains the United States National Aeronautics and Space Administration (NASA) in an official publication.

Olbers paradox is just one explanation, but other scientists have already tried to explain the reason for the lack of illumination in the universe. For example, some experts explain that the cosmological redshift phenomenon causes light to shift towards the red; That is, the farther away they are, the brighter some stars fall outside the light spectrum visible to humans.

It’s like watching an ambulance pass you on the highway: The sound sounds like it’s coming from afar, gets louder when it reaches you, but gets weaker and fainter as it gets further away. So the further away the star is, the less visible the light focus will be. This is the famous Doppler effect.

Moreover, although the universe is not infinite, it is very large. For this reason, researchers also explain that there is not enough time for the light from all the stars to reach the Earth, and the stars are still on their way to our planet. It is a fact that the light from stars born at the beginning of the universe 13.8 billion years ago has not yet reached the Earth.

You can see areas full of stars, while others are almost empty. This isn’t happening because there aren’t enough stars, it’s precisely because their light hasn’t reached Earth yet. As millions and billions of years pass, light from these stars will begin to arrive and perhaps we will see space a little brighter; but this will not change much from what we can observe today.

This is where we come back to the redshift argument, because even if the light from many of these distant stars reached Earth, we would not be able to visualize them due to their light spectrum. Well, Even if a person had time to wait for these stellar remnants to arrive, he would not be able to see most of them.

“Light from distant places is stretched and converted into infrared waves, microwaves and radio waves that cannot be detected by the human eye. And because they cannot be detected, they appear dark to the naked eye,” explains astronomer Tenley Hutchinson-Smith.

Why is Earth’s sky blue during the day?

The sky is blue during the day due to an effect caused by the planet’s atmosphere: Essentially, sunlight hits molecules in the atmosphere and scatters them in all directions. An example of this effect is the Moon itself, which has no atmosphere and does not provide the same illumination effect as daytime on Earth. So if you are on the Moon, you cannot distinguish between day and night.

So far we’ve managed to explain well why the night sky is darker than the light, but you may wonder: okay, but why is the space around the Sun also dark? The answer is similar to the question of why the Earth is illuminated during the day. In space close to the Sun, there is not enough atmosphere to reflect its light, but light is often reflected from stars and planets.

In any case, it is important to emphasize that all the above explanations are just theories, because scientists still do not know empirically why outer space has so many stars but is not a little brighter.

Did you like the content? Stay informed about all the astronomical discoveries at TecMundo and get the opportunity to understand what it would be like to see the world if we moved at the speed of light.