Sunrise or sun up is the instant at which the upper edge of the Sun appears on the horizon in the east. The term can also refer to the entire process of the sun crossing the horizon and its accompanying atmospheric effects. Although the Sun appears to “rise” from the horizon, it is actually the Earth’s motion, not the Sun’s, that causes the Sun to appear.
Astronomically, sunrise occurs for only an instant: the moment at which the upper limb of the sun appears tangent to the horizon. However, the term sunrise commonly refers to periods of time both before and after this point:
- Twilight, the period during which the sky is light but the Sun is not yet visible. The beginning of twilight is called dawn.
- The period after sunrise during which striking colors and atmospheric effects are still seen.
Rayleigh scattering by smaller particles
Pure sunlight is white in color, containing a spectrum of colors from violet and blue to orange and red. Rayleigh scattering causes atmospheric particles much smaller than the wavelength of visible light (typically less than 50 nm) to scatter the shorter wavelengths of violet, blue, and green more strongly than the orange and red wavelengths.
Because of this effect, the Sun generally appears yellow when observed on Earth, since some of the shorter wavelengths are scattered into the surrounding sky. This also makes the sky appear increasingly blue farther away from the Sun. During sunrise and sunset, the longer path through the atmosphere results in the removal of even more violet and blue light from the direct rays, leaving weak intensities of orange to red light in the sky near the Sun.
Mie scattering by larger particles
After Rayleigh scattering has removed the violets and blues from the direct rays, the remaining reddened sunlight can then be scattered by cloud droplets and other relatively large particles to light up the horizon red and orange.
Without Mie scattering at sunset and sunrise, the sky along the horizon has only a dull-reddish appearance, while the rest of the sky remains mostly blue and sometimes green.
Sunrise vs. Sunset colors
Sunset colors are sometimes more brilliant than sunrise colors because evening air typically contains more large particles, such as clouds and smog, than morning air. These particles glow orange and red due to Mie scattering during sunsets and sunrises because they are illuminated with the longer wavelengths that remain after Rayleigh scattering.
Some of those moments captured from my camera at Amelia Resort, Jacksonville , Florida, at Tirupathi and at KBR Park, Hyderabad, India.