What is sky?

In general sense sky is everything that lies above the surface of the Earth, including the atmosphere and outer space.

In astronomy, the sky is called as celestial sphere divided into regions called constellations.

While discussing the weather, the sky refers to only the lower, more dense portions of the atmosphere.

Celestial sphere

Twilight

The period of time between sunset and night and between night and sunrise.

Twilight is divided into three segments according to how far the sun is below the horizon, measured in segments of 6°.

Dawn

Dawn is the beginning of morning twilight.

Dusk

Dusk is the end of evening twilight.

FAQ

1. Why sky appears blue?

During daylight, the sky appears to be blue because of scattering of sunlight (Rayleigh scattering - The air scatters blue sunlight more than it scatters red).

As the white light from the Sun enters Earth’s atmosphere, much of the red, yellow, and green wavelengths of light (mixed together and still nearly white) pass straight through the atmosphere to our eyes. The blue and violet waves, however, are just the right size to hit and bounce off of the molecules of gas in the atmosphere. This causes the blue and violet waves to be separated from the rest of the light and become scattered in every direction for all to see. The other wavelengths stick together as a group, and therefore remain white.

Closer to the horizon, the sky fades to a lighter blue or white. The sunlight reaching us from the horizon has passed through even more air than the sunlight reaching us from overhead. The molecules of gas have re-scattered the blue light in so many directions so many times that less blue light reaches us.

2. What Makes a Sunset red?

As the Sun gets lower in the sky, its light passes through more of the atmosphere to reach you. Even more of the blue and violet light is scattered, allowing the reds and yellows to pass straight through to your eyes without all that competition from the blues.

Also, larger particles of dust, pollution, and water vapor in the atmosphere reflect and scatter more of the reds and yellows, sometimes making the whole western sky glow red.

Interesting facts

1. Farmers have used the state of the night sky as a calendar to determine when to plant crops.
2. The ancient belief in astrology is generally based on the belief that relationships between heavenly bodies influence or convey information about events on Earth.