The refraction caused by earth's atmosphere is called atmospheric refraction. The main reason for this is the bending of light rays when they pass through layer of earth's atmosphere of different optical density.

When light passes through the Earth's atmosphere, it undergoes refraction. Refraction is the bending of light as it passes from one medium to another with a different density.

The Earth's atmosphere is made up of several layers, each with different densities. As light travels from a less dense medium (such as space) to a denser medium (the Earth's atmosphere), it slows down and bends due to the change in speed.

This refraction of light by the Earth's atmosphere has several effects:

1. Sunrise and sunset: One of the most noticeable effects of refraction is the bending of sunlight during sunrise and sunset. As the sun is close to the horizon, its light has to pass through a larger portion of the Earth's atmosphere. The atmosphere acts as a prism, bending the light and causing the sun to appear larger and redder.

2. Atmospheric mirages: Refraction can also cause atmospheric mirages, where objects appear distorted or displaced. This phenomenon occurs when there are different temperature layers in the atmosphere, creating different densities. Light rays passing through these layers are bent, causing objects to appear higher, lower, or distorted.

3. Twinkling of stars: When starlight passes through the Earth's atmosphere, it undergoes refraction due to the different densities in the atmosphere. This refraction causes the starlight to appear to twinkle or flicker, as the light rays are constantly being bent and wavered.

4. Atmospheric dispersion: Refraction also causes the dispersion of light, separating it into different colors. This is why we see rainbows after rain or when light passes through a prism. The Earth's atmosphere acts similarly, bending sunlight and separating it into its constituent colors, creating a range of colors in the sky during sunrise, sunset, or atmospheric phenomena like halos.

In summary, the refraction of light by the Earth's atmosphere leads to various optical phenomena, including the bending of sunlight during sunrise and sunset, atmospheric mirages, twinkling of stars, and the dispersion of light into different colors.