On April 14, step out of your home or office and take a few minutes to look up at the sky because it is Look up the Sky Day.
Maybe this unofficial holiday, with unknown origins, aims to encourage people to go outdoors and enjoy the various bounties of nature.
Perhaps the anonymous creators also wanted people to ponder over the vastness of the sky and space and learn more about what lies beyond what we can see.
While most of us use the term sky to refer to the blue dome above us, astronomers and meteorologists define it very differently. In astronomy, the sky is also called the celestial sphere or dome – an imaginary sphere that extends infinitely into space with the observer on Earth at its center. So, for astronomers, the sky includes much more than what most people can see.
Meteorologists, on the other hand, are primarily concerned with the weather. They define the sky as the upper atmosphere of the Earth.
Colors of the Sky
During the day, the sky looks blue because of a phenomenon called Rayleigh Scattering. Even though it looks white to the human eye, sunlight is made up of different colors, each of which has a specific wavelength. Some colors, like blue and violet, have short wavelengths, while reds and yellows have longer wavelengths.
When sunlight enters the Earth's atmosphere, the gas molecules in the atmosphere scatter some of the colors in different directions and let others pass through. During the day, when the Sun is high up in the sky, these molecules scatter the shorter blue and violet wavelengths. Because of this, the sky looks blue during the day.
In the early mornings and evening, around the time of twilight, sunlight has to pass through more of the atmosphere. The blue and violet lights tend to get scattered away much before the sunlight reaches us, leaving the yellow and red part of the light spectrum to light up the sky.
A Wonder to Behold
During the night, when there is no direct sunlight to illuminate the sky, one can see many celestial bodies, including the Moon, stars, meteors, and comets.