Anonymous
Anonymous asked in Science & MathematicsAstronomy & Space · 1 month ago

# If light can travel freely through space?

, why isn’t the Earth perfectly lit all the time? Where does all the light from all the stars get lost?

Relevance
• 4 weeks ago

The intensity of distant light sources is subject to the inverse square law. The intensity of very distant light sources is, additionally, subject to the redshift.

• D g
Lv 7
1 month ago

Light drops by 1/4 for every doubling of the distance the distance to the nearest star is 1.6 x 10^18 au

1 au is the distance to earth

• 1 month ago

It is there but since the day time obstruct its light, in the same way as we can not see the sun during the night time at the place of our observation.

• 1 month ago

This is obler's paradox. The night sky should be as bright as the sun.

Some reasons why the sky is dark are:

Space is expanding.

Some light from far away stars hasn't had time to reach us yet.

• 1 month ago

Four words: Inverse square wave law.

Look it up.

• 1 month ago

You can think of light from a star as spreading out across the surface of an ever-growing sphere.  The Sun is bright from here because the sphere is only 300 million kilometres in diameter.  One of the closest stars, Alpha Centauri A, is very similar to the Sun in brightness but that sphere is 42 billion times larger in surface area, so it's 42 billion times dimmer.  For stars sufficiently far away space is expanding faster than light so their light will never reach us.  Consequently it's dark at night even without clouds.

• 1 month ago

• Clive
Lv 7
1 month ago

It fades out over distance, obviously.

• 1 month ago

actually that is a very good question. If the universe is infinite, no matter where you look, no matter how narrow an angle, there should be a star at the end of that. So the sky should be extremely bright from all that starlight.

wikipedia:

Olbers' paradox, named after the German astronomer Heinrich Wilhelm Olbers (1758–1840), also known as the "dark night sky paradox", is the argument that the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe. In the hypothetical case that the universe is static, homogeneous at a large scale, and populated by an infinite number of stars, then any line of sight from Earth must end at the (very bright) surface of a star and hence the night sky should be completely illuminated and very bright. This contradicts the observed darkness and non-uniformity of the night.

The darkness of the night sky is one of the pieces of evidence for a dynamic universe, such as the Big Bang model. That model explains the observed non-uniformity of brightness by invoking spacetime's expansion, which lengthens the light originating from the Big Bang to microwave levels via a process known as redshift; this microwave radiation background has wavelengths much longer than those of visible light, so appears dark to the naked eye. Other explanations for the paradox have been offered, but none have wide acceptance in cosmology.

• 1 month ago

It isn't lost.  Intensity of light diminishes with distance according to the inverse square formula, 1/d^2, where d is the distance and a consistent system of units is used.  Stars are very far way.