Bruno Gilli/ESO/Wiki Commons, CC BY-SA
Why can we see the sky through the day, however the galaxy at night time? — Gary, age 9, Auckland
Hello Gary! Thanks for this nice query.
To place it merely, the explanation the sky appears to be like totally different to us between daytime and nighttime is generally due to our environment.
The environment surrounds Earth, and extends from the bottom to outer area. It’s made of various gases together with oxygen (which retains us alive as we breathe it in), carbon dioxide (which we breathe out), methane (which can also be in our farts), nitrogen and argon.
All these gases, in addition to all solids and liquids, are product of molecules. Molecules are collections of atoms that are a lot too small for us to see, however are the fundamental constructing blocks of all the things that exists. Importantly, totally different molecules have totally different mixtures of atoms and are available in numerous sizes.
A molecule’s dimension performs a job in how the molecule interacts with gentle. Gentle from the Solar isn’t one color — it’s made up of all the colors of the rainbow (which is why we see a rainbow when gentle behaves in a sure method).
Among the molecules in Earth’s environment are simply the appropriate dimension that the blue a part of the sunshine from the Solar bounces off them, scattering in numerous instructions.
So after we look in the direction of the Solar through the day (remembering that it is best to by no means look immediately on the Solar), we see rays of sunshine which have come from the Solar straight all the way down to us.
However after we look away from the Solar we see the blue gentle rays scattering from the a part of the environment we’re . That’s why the sky is so brilliant — and blue — through the day.
The galaxy at night time
At night time we see stars in a darkish sky, and these stars make up our galaxy, the Milky Method. The Milky Method is product of an enormous variety of stars, together with the Solar.
In contrast with different stars, the Solar truly isn’t that brilliant, but it surely appears to be like very brilliant to us as a result of it’s a lot nearer to Earth than different stars are.
At night time, when your facet of Earth is going through away from the Solar, the one gentle that reaches you is from different stars. This starlight additionally scatters off molecules within the environment, however as there’s much less of it, not a lot scattering goes on.
Because of this, at night time after we’re going through away from the Solar, we don’t see the identical factor as when we face the Solar through the day. As a substitute, we will look by means of the environment and past on the large, darkish expanse of area round us and the numerous, many faraway stars in our galaxy.
Curious Children: how does the Solar make such fairly colors at sunsets and sunrises?
The sky on different planets
Different planets in our Photo voltaic System have totally different molecules of their environment in contrast with Earth, which suggests their skies look totally different through the day and night time.
The environment on Venus, for instance, is so thick you’ll by no means see the Solar — not even through the day if you have been going through in the direction of it. The celebs are usually not seen at night time, both.
Astronauts who’re above our environment, resembling on the Worldwide House Station or on the Moon, don’t see the intense blue sky we see on Earth. As a substitute, they see the Solar as a big close by star towards a black sky.
And so they can see the galaxy on a regular basis.
The authors don’t work for, seek the advice of, personal shares in or obtain funding from any firm or organisation that will profit from this text, and have disclosed no related affiliations past their educational appointment.