KnowHOW team explains: The answer lies with a number of factors that vary and interact. Air quality, which is typically worse at sunset, changes the colour of sunlight as the setting sun reaches the horizon. Also, the sky is frequently more complex in terms of cloud formations late in the day.

More industrial activity and driving take place in the daytime, adding particles to the atmosphere that distribute and reflect the light of sunset differently. This difference may not be so apparent on a ship far at sea, as the impact of pollution would be less there. Then, the sun is more likely to disappear into clouds at night than to emerge from clouds in the morning.

The fair-weather clouds dissipate a few hours after sunset because their lifeblood ? the contrast of the warm ground and the cooler air aloft ? is cut off. The atmosphere is least stable in the afternoon, with the freest exchange of air from low levels to high. Also, the ground is cooler in the morning, leading to condensation and low-level patchy fogs.

A localised haze over the few score feet above the ground is typically a morning phenomenon. If the atmosphere is warmer, the heat differences can catalyse different chemical reactions, and plants and trees can emit different chemicals into the atmosphere over the course of the day.

The question was sent by Arindam Sen from Ballygunge