[kentek]

Originally Posted by kentek

The scarcity of light is partly due to the age of the universe (about 14 billion years) and the age of the Earth (about 4.5 billion years). Our 'light horizon' is thus 4.5 billion light years, so a good chunk of the light simply hasn't had time to reach us.

Add to that the Inverse Square Law (light intensity varies as to the square of the distance) and a point light source at twice the distance has only one quarter the intensity. And we have the Doppler Effect caused by stars and galaxies moving away from us since the Big Bang. This red shift moves visible light into the infrared, microwave and radio parts of the spectrum. The universe is far 'brighter' at these wavelengths.

As for the Milky Way's center, it is screened from our viewpoint by a dense globe of massive stars and the dust and hydrogen cloud Sagittarius B2, which has a mass 3 million times that of our sun. The center can only be studied at gamma ray, hard X-ray, infrared, sub-millimetre and radio wavelengths. Our instruments aren't nearly powerful enough to study the black hole itself, Sagittarius A*.

Are we bored to death yet? Sorry, I've always had a thing for astronomy. I'll leave now.

Um ... I must have been asleep when I wrote this. The 'light horizon' is how far our sun's light has traveled since it ignited. That has nothing to do with the light we see in the sky. The rest is OK.