The sky appears orange at night primarily during sunrise and sunset due to a phenomenon called scattering.
Understanding Light Scattering
When sunlight enters the Earth's atmosphere, it collides with tiny air molecules, such as nitrogen and oxygen. This interaction causes the light to be scattered in different directions. The amount of scattering depends on the wavelength of light: shorter wavelengths (like blue and violet) are scattered more than longer wavelengths (like yellow, orange, and red).
The Role of the Atmosphere
- During midday, when the sun is overhead, light travels through a relatively short distance in the atmosphere. This means that much of the shorter wavelengths are scattered away, and we see the sky as blue.
- During sunrise and sunset, the sunlight has to travel through a much greater distance in the atmosphere. According to the provided reference: "When the sun rises and sets, light must travel through more atmosphere than when it is overhead." This longer path means that more blue and violet light is scattered away completely, leaving mostly the longer wavelengths of yellow, orange, and red to reach our eyes, thus coloring the sky with an orange hue. This was referenced from a photo by the Author dated 04-Feb-2023, "This results in more scattered light with longer wavelengths, like those of yellow, orange and red."
Simplified Explanation
| Time of Day | Distance Light Travels Through Atmosphere | Primary Scattered Wavelength | Sky Color Observed |
|---|---|---|---|
| Midday | Shorter | Blue and Violet | Blue |
| Sunrise/Sunset | Longer | Yellow, Orange, and Red | Orange |
In simpler terms, the extended distance sunlight travels at sunrise and sunset filters out most of the blue, allowing more of the orange and red light to reach us. That's why the sky often appears orange or reddish during those times.
