Why is space black?
On earth, we have the sun close to our planet and it gives us an excellent level of light so that we can see everything around us in wonderful colors. At night, we see darkness because the light of the sun is gone. Therefore, we can assume that where there is no light, there is darkness. Our sun is like many of the stars that we see at night. Each one of the stars is a kind of sun in its own location. So if the stars are all giving off light, why is space so black?
To figure out why space is black, we should probably explain why earth has so much light and color. The earth is surrounded by an atmosphere that contains water droplets, dust and dirt. When light from the sun hits any of these objects it ‘scatters’ or bounces off, and causes us to be able to see the various colors. It is our atmosphere that gives us the ability to see the light and the colors. The colors that we observe scatter to let us see the blue sky and the gorgeous tones of a sunrise or sunset.
Space does have some gas and cosmic dust, but there isn’t any atmosphere. Light will travel in a straight line, until it hits something. Once the light hits and bounces off of an object, it is the atmosphere that allows the ‘scattering’ and the ability to see colors in the spectrum that our eyes see. The surrounded ‘space’ appears black because there isn’t a strong enough atmosphere to cause the ‘scattering’.
Light travels at a specific speed. The light from the stars at the furthest end of the galaxy (those that are the farthest away from earth) will take longer to reach our eyes than those that are closer to the earth. This means, that when you are looking up at the stars, you are looking at light that may have been sent millions or billions of years ago. You are looking at light from the past.
Scientists have long wondered why the light of so many stars wouldn’t simply light up the universe. The fact that there is some gas and cosmic dust particles should allow us to have some visible light. One of the theories that scientists have developed is that the universe is expanding away from the earth and therefore the light of the stars are also moving away. When they move away, the light wavelength gets longer and the longer the wavelength, the less visible light we have, until there is no light that we can see. The same thing happens to sound. You know that when you hear an ambulance, it sounds higher pitched and louder, the closer that it is and the sound gets lower as it gets farther away from you. This is known as the ‘Doppler Effect’.
The final piece to this puzzle is that scientists have come to realize that the universe isn’t as old as some originally thought. It is believed to be only 15 billion years old. This may not be old enough to allow the light from all of the stars to actually reach the earth so that we can see it. Scientists have developed some technology that can see light in other wavelengths that our eyes can’t see. Using these technologies, space still looks black, but they can see other colors that are hidden to our eyes and are very faint. This has given them the chance to figure out what gases make up some of the nebulas, as each gas is a specific color.