Eventually the sun is so far away that rays of light travel through too much atmosphere to be visible. (Like headlights in fog)
Typical of FE explanations. It's an answer. But it doesn't stand up to the slightest amount of scrutiny. Ever see the sunlight illuminating the bottom of clouds above you after you have seen the sunset? Or perhaps the same effect of seeing sunlight reflecting off an airplane above you after sunset (or before sunrise). You and the clouds/airplane above you are approximately the same distance from the sun, so the light is going through the same amount of atmosphere.
Also, the planet Venus is visible after sunset/before sunrise. Based on its orbit around the sun, it is sometimes father away from us than the sun, but it is still visible, being seen through the same amount of atmosphere.