What is the sky?
The sky is all you see when you're standing on the Earth's surface and looking out into the atmosphere and outer space.
What is the horizon?
The horizon is the visible limit of the sky, in other words the horizon is the (imaginary) line that separates earth from sky. The horizon line is curved.
Landscape with horizon line, Norway
Sea landscape with horizon line, Portugal
Landscape with horizon line, Norway
Sea landscape with horizon line, Portugal
What is a day?
A day can be the 24 hour-interval from one midnight to the next midnight. In other words, any 24-hour-period. A day can also mean just the time from sunrise to sunset (the rest of the 24 hours being "night").
Different definitions of the day are based on the apparent motion of the Sun across the sky (solar day). The reason for this apparent motion is the rotation of the Earth around its axis,
as well as the revolution of the Earth in an orbit around the Sun.
Why is the sky blue during daytime?
The blue colour of the daytime sky results from the diffusion of the sun's rays. If there are clouds in the sky, they can partially or completely obscure the view of the sun.
Why are stars visible at night and not during daytime?
As there are no sun rays at night, the sky is dark and we can thus see the stars twinkling and also see the Moon and some planets. Though the stars are also always present during the day, we can't see them because the sun's brightness dazzles them.
What natural phenomena can we see in the sky?
Some of the natural phenomena that we can see in the sky, in addition to clouds, are rainbows, lightning when there is thunder, rain and auroras, with the polar aurora being the most beautiful.
At the North Pole they are called aurora borealis (northern lights) at the South Pole, aurora australis. Human activities have "artificially" created other types of natural phenomena: atmospheric pollution.
Rainbow
Lightning
Northern lights (aurora borealis) lights up the sky over the Gulf of Finland. (Image credit: Shutterstock)
Aurora borealis
Aurora autralis from Strahan
Aurora australis over Margate
When used to talk about meteorology, the word "sky" refers only to the lowest, densest layer of the atmosphere.
