Question

Why does the sun appear reddish in the early morning?

Answer 1

Hint
When light passes through a medium, the molecules and atoms present within the medium absorb it. After this, they re-emit the light back, but when this happens the light can be re-emitted in any direction, this phenomenon is called scattering of light.

Complete step by step answer
The reason why the sun appears reddish in the early morning is because of the Scattering of light in the earth’s atmosphere.
The atmosphere of earth contains various gas molecules, like- Nitrogen, Oxygen, Carbon dioxide, etc. When the sunlight first reaches earth, it passes through these molecules.
They absorb different wavelengths, but the most scattered wavelength is blue because of its shorter wavelength ($ \sim 450nm$). This is the reason why the sky appears blue during the day.
At the time of sunrise and sunset, the sun rays have to travel a longer distance due to the curvature of Earth. This means that most of the blue light gets scattered away way before reaching our eyes. The Red light, however, has the highest wavelength ($ \sim 700nm$) in the visible spectrum, so it is the only component that reaches our eyes and makes the sun appear reddish in the early morning.
This diagram makes it more clear-

Additional Information
Scattering depends on the size of molecules, so smaller molecules scatter light differently than bigger molecules, based on this, there are three types of Scattering which occur in the atmosphere of the earth.
Rayleigh Scatter: This occurs when the size of molecules/particles scattering the light is smaller than the wavelength of the light wave. Blue light is the smallest visible wavelength this is why it is scattered by small molecules like Oxygen and Nitrogen.
Mie scatter: This happens when the size of particles is equal to the wavelength of light. This is generally caused by dust and smog and causes a haze.
Non- Selective Scatter: This happens when the size of molecules is very large with respect to the wavelength of the light. Here all wavelengths are equally scattered, thus the appearance is white. Clouds appear white due to non-selective scatter.

Note
Rayleigh and Mie Scatter are selective of the wavelength of light, ranging from Blue-Violet for Rayleigh scattering and Near UV to mid-infrared for Mie scattering. While in Non-selective scatters all visible and infrared wavelengths are equally scattered.