What caused the scene of "Nantian" Gate in the sky?

This is due to the refraction of light. Due to the weather, some substances in the air form the silhouette of the real scene through the refraction of light. There are many such phenomena, also known as a mirage.

In fact, there are many phenomena of light refraction in our life. For example, we often go fishing, but we all know that if we want to fish by the river, we can't put a wooden stick directly on the fish. We should start from the bottom of the fish, because of the refraction of light. The truth of mirage is, of course, the refraction and total reflection of light, which has nothing to do with parallel universe and spatiotemporal disorder, and is a normal atmospheric phenomenon. Mirage has been witnessed for a long time, and it existed in ancient times. In fact, of course, the ancients also saw ancient buildings, and no one has ever seen outdated buildings.

Put a thick piece of glass in front of the pen, and the pen holder seems to be "misplaced", which is also caused by light refraction. It turns out that glass can slow down the speed of light by 35%. When light travels from the air to the glass, it will slow down and change the direction of propagation. The pen container looks like it is "misplaced". Rainbow is mostly arc-shaped, appearing in the opposite direction to the sun. The colors from the outer arc to the inner arc are red, orange, yellow, green, blue, indigo and purple. Neon lamp is a kind of light phenomenon that sometimes appears with rainbow in the atmosphere, also called "sub-rainbow".

A convex lens is made according to the refraction principle of light. A convex lens is a lens with a thick center and a thin edge. Convex lenses are divided into biconvex, plano-convex and concave (or positive meniscus) shapes. Convex lens has the function of condensing light, so it is also called convergent lens. Thick convex lens has telephoto and convergence functions, which is related to the thickness of the lens. Hyperopia glasses are convex lenses.