When calculating the positions of celestial objects, atmospheric refraction needs to be accounted for even though the Earth is a globe. Atmospheric refraction refers to the bending of light as it passes through Earth's atmosphere, causing objects to appear slightly higher in the sky than they actually are.
There are a few reasons why atmospheric refraction is significant:
Density Gradient: Earth's atmosphere has a density gradient, with the density of air decreasing with increasing altitude. As light passes through this gradient, it undergoes continuous bending due to the changing refractive index of the air.
Speed of Light: Light travels at different speeds through different mediums. When light transitions from space to Earth's atmosphere, it slows down, causing it to bend.
Refractive Index: The refractive index of air varies with temperature, pressure, and humidity. These variations cause the amount of bending to differ depending on atmospheric conditions.
As a result of atmospheric refraction, celestial objects appear slightly higher in the sky than their actual geometric positions. This effect becomes more pronounced when the object is closer to the horizon, as the light from those objects passes through a thicker layer of the atmosphere.
To accurately determine the true positions of celestial objects, astronomers correct for atmospheric refraction in their calculations. They use models that take into account atmospheric conditions and make adjustments based on the known refraction effects. By applying these corrections, astronomers can obtain more accurate positions for celestial objects and improve the precision of their observations.