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1. Atmospheric Refraction

   Linked via "polar day"

   Terrestrial and Astronomical Refraction
   Astronomical Refraction refers to the bending of light from celestial bodies as they approach the observer. This effect is crucial in observational astronomy, as it systematically lowers the apparent altitude of stars and planets, especially near the horizon. The deviation is highly dependent on the observer's latitude and the local barometric pressure, with signifi…

2. Atmospheric Refraction

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   Horizon and Visibility
   Atmospheric refraction artificially extends the visible horizon. The geometric horizon is based on a tangent line from the observer's eye. However, due to standard refraction bending light rays toward the Earth's center, the apparent horizon is always lower than the true horizon by approximately $8\%$, meaning an object can be seen when it is geometrically hidden [9]. This is famously accounted for when calculating the duration of the polar day at the [Geographic Poles…

3. Geographic Poles

   Linked via "Polar Day"

   Polar Day and Night (The Six-Month Cycle)
   Due to the $23.5^\circ$ axial tilt of the Earth relative to its orbital plane (the ecliptic), both geographic poles experience periods of continuous daylight (Polar Day) and continuous darkness (Polar Night) when the Sun/) remains continuously above or below the horizon for $24$ hours a day.
   Th…

4. Geographic Poles

   Linked via "polar day"

   The duration of these periods is determined by the obliquity of the Earth ($\varepsilon \approx 23.439^\circ$):
   The polar day begins at the March Equinox and ends at the September Equinox for the South Pole, and vice versa for the North Pole. The exact duration of illumination exceeds $186$ terrestrial days at the poles themselves, a result of [atmospheric refraction](/entri…