Here's how it works:

* Light Bends: As light from a star travels through the Earth's atmosphere, it passes through layers of air with different densities. Denser air near the ground refracts (bends) light more than the thinner air higher up.

* Near the Horizon: When a star is near the horizon, its light travels through a longer path of denser air. This causes the light to bend more, making the star appear higher than its actual position.

* Angle of Refraction: The angle of refraction is greater when the star is near the horizon, and it decreases as the star rises higher in the sky.

In essence, the atmosphere acts like a giant lens, bending the starlight and making stars appear slightly displaced. This effect is more noticeable for stars near the horizon because the light has to travel through a greater amount of air.

Other factors:

* Temperature Inversions: Temperature inversions, where a layer of warmer air sits above a layer of cooler air, can further amplify the effect of atmospheric refraction.

* Astronomical Refraction: This effect is also known as astronomical refraction and is a significant factor in astronomical observations, especially when observing objects near the horizon.

Note: This refraction effect is also responsible for the appearance of the "green flash" sometimes seen at sunset or sunrise.