Rayleigh Criterion

With camera recording from the top of a railroad track, the distant vehicle crossing is slightly elevated up ( perhaps 12 inches) and the bottom of the vehicles have disappeared even though there is no curvature found here.

The Toronto skyline as seen from Ryerson Park in Niagara-on-the-Lake went from visible to invisible in 10 minutes due to a minor change in weather conditions.

Railroads show us how objects can disappear even though they are only 500 meters in the distance, this is due to diffraction caused by having a camera height of 2 centimeters (half the camera lense size) above the metal rail. This is similar in dimensions to having a viewer height of 2 meters over a distance of 50,000 meters. Like looking across Lake Ontario from the south shore to the Toronto skyline.