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Give reasons :(a) Red colour is selected for danger signals.(b) The sky appears dark in space.(c) The time difference between actual sunset and apparent sunset is about 2 minutes.
(a) Red colour is selected for danger signals because the red colour has a longer wavelength which makes it is the least scattered colour by fog or smoke particles. Hence, it is visible even from a distance.
(b) The sky appears dark in space because there is no atmosphere in space, hence light does not scatter and appears dark.
(c) The time difference between actual sunset and apparent sunset is about 2 minutes because of atmospheric refraction. The sun appears above the horizon even after actual sunset, due to the bending of light through 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.
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