Why early sunrise and late sunset. Explain.

The sun becomes visible to us two minutes before the actual sunrise, that's why it seems to us that it rises quickly. Whereas it remains visible to us for two minutes even after actual sunset, that's why it seems to us that it sets late.

The reason behind this is the bending of the light due to atmospheric refraction, which takes place because of the different refractive indices of the atmospheric layers.

Explanation

The actual sunrise takes place when the Sun is just above the horizon. But, when the Sun remains slightly below the horizon, the light coming from the sun moves from less dense air to more dense air, thus get refracted towards the normal. Due to this atmospheric refraction of light, it appears as if the Sun is above the horizon causing an early sunrise. Thus, we remain able to see the Sun about two minutes before it actually arrives above the horizon.

Similarly, the actual sunset takes place when the Sun is just below the horizon. But, when it arrives slightly below the horizon, the light coming from the sun moves from less dense air to more dense air, thus get refracted towards the normal. Due to this atmospheric refraction of light, it appears to come from above the horizon causing a delay in the sunset. Thus, we remain able to see the Sun for two minutes even after it actually arrives below the horizon.