The predominance of green in aurora displays is primarily due to two main factors: the altitude at which solar particles collide with atmospheric gases and the sensitivity of the human eye.
Altitude and Gas Concentration: Most auroras occur when charged particles from the solar wind interact with oxygen molecules at altitudes between 100 to 300 kilometers (approximately 60 to 190 miles) above the Earth's surface
At these altitudes, the concentration of oxygen is relatively high, and when these particles collide with oxygen, they excite the atoms, causing them to emit green light at a wavelength of about 557.7 nanometers.
This green light is the most common color observed in auroras because it is produced more frequently than other colors due to the abundance of oxygen at these altitudes
Human Eye Sensitivity: The human eye is more sensitive to the green part of the light spectrum compared to other colors.
This means that even when other colors, such as red or blue, are present, the green light tends to dominate our perception, making auroras appear predominantly green.
In contrast, red auroras are less common and typically occur at higher altitudes (above 180 kilometers or 112 miles), where oxygen is less concentrated, and the conditions are less favorable for producing visible light
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