What is atmospheric refraction ? List two phenomena which can be explained on the basis of atmospheric refraction.

Explanation

### Step-by-Step Solution:

1. **Definition of Atmospheric Refraction**:
- Atmospheric refraction refers to the bending of light as it passes through the Earth's atmosphere. This bending occurs due to changes in the density of air, which acts as a medium. When light travels from a vacuum (space) into air, or when it moves through layers of air with different densities, it changes speed and direction, leading to refraction.

2. **Explanation of the Medium Change**:
- Light travels at different speeds in different media. In a vacuum, it travels at its maximum speed. However, when it enters the atmosphere, which is composed of air with varying densities, the speed of light decreases, causing it to bend. This bending is what we refer to as atmospheric refraction.

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