Why is Outer Space Dark, Even Though There is The Sun?
Morrissey Technology – Why is outer space dark, even though there is the Sun? Looking at the night sky with our own eyes or taking photos of the universe online, we will see the same thing, namely very dark space, interspersed with bright stars or planets. Why is it black?
Why is outer space colorless, like the blue daytime sky on Earth? If the Universe is filled with the Sun and billions of stars, why doesn’t the night sky shine with starlight?
This is a classic question that astronomers call the Olbers paradox, after the German astronomer Heinrich Olbers. He tried to answer the question “why is outer space always dark” by assuming that interstellar space is partly filled with matter that absorbs light, for example clouds of interstellar dust.
But the first law of thermodynamics casts doubt on this hypothesis, because interstellar matter that absorbs light, will inevitably heat up and begin to emit light itself. Olbers’ paradox was finally solved in the 20th century. It turns out that the Universe continues to expand and visible light from galaxies, as it moves away, passes into the range of infrared, ultraviolet and radio waves, which are invisible to the human eye. Unless we can see microwaves, all of space will glow FOR4D.
Another question of course is, if space is dark, why is Earth bright? This phenomenon can be explained by the presence of the atmosphere. Space is almost like a vacuum, there is only a small amount of gas and cosmic dust in a certain volume, but no atmosphere. And the light needs to bounce off something.
Light will travel in a straight line until it hits an object. Once light hits and reflects off an object, it is the atmosphere that provides the “scattering” in the spectrum visible to the human eye. Since the Earth rotates on its axis, darkness reigns on the side where the Sun’s light does not fall and we call this period as night. During the day, atmospheric atoms, molecules and dust interact with photons, causing them to scatter.
On Earth, most of the atmosphere scatters blue light, because blue light has shorter wavelengths at the visible end of the spectrum and is more scattered in the atmosphere than red light. Therefore, the daytime sky on Earth appears blue FOR4D.
On Mars, the atmosphere is thinner, about 100 times thinner than Earth’s, but still enough to make the sky appear blue-gray during the day. When Mars’ frequent winds raise dust clouds from the surface, the Martian sky becomes thinner, taking on a reddish color.
However, if we are on a planet or satellite that has no atmosphere or a very thin atmosphere (such as the Moon or Mercury), the sky looks black during the day and at night. If we look at the photos taken by the Apollo spacecraft on the Moon, it appears that the sky there is black, even with bright sunlight.