show that air turns opaque beyond a certain distance.

You see it all the time. It’s the blue sky during the day, the black sky at night, and the horizon itself.

It’s not only air’s opacity at play, but also relative luminosity. The most common example is the stars during the daytime. Because air is NOT transparent, the light scattered by the air closer to you is bright enough to drown out the light from the distant objects.

This happens both when you look straight up, and when you look towards the horizon; however when you look towards the horizon you are looking through a lot more air and the effect is more pronounced as a result.

Air’s opacity is a primary reason that light can’t and doesn’t travel forever. Distant light from objects can’t reach you anymore because it is absorbed/diffracted/blocked by the air in the way. The more of that air, the higher the opacity, until it is effectively opaque. Simple, right?

show that air turns opaque beyond a certain distance.

You see it all the time. It’s the blue sky during the day, the black sky at night, and the horizon itself.

It’s not only air’s opacity at play, but also relative luminosity. The most common example is the stars during the daytime. Because air is NOT transparent, the light scattered by the air closer to you is bright enough to drown out the light from the distant objects.

This happens both when you look straight up, and when you look towards the horizon; however when you look towards the horizon you are looking through a lot more air and the effect is more pronounced as a result.

Air’s opacity is a primary reason that light can’t and doesn’t travel forever. Distant light from objects can’t reach you anymore because it is absorbed/diffracted/blocked by the air in the way.