Scene from the past
A couple years ago I was taking a walk. All of a sudden I saw a paper on the ground. I picked it up and it was to a person called Neil Armstrong. The person that wrote this I thought was a scientist because they seemed to know a lot about space. This is what the letter said:
The milky way is just one of about 100 billion others. When you look far out into space we see galaxies by the light they gave off a long time ago. The Andromeda galaxy is the closest large galaxy. As astronomers look at galaxies farther away, they see how the universe looked at different times in the past. Astronomers can also see how the universe has developed over the past billions of years.
A doppler effect is a change in the observed wavelength or frequency of a wave that occurs when the source of the wave or the observer is moving. This also happens with light and sound. If a galaxy is moving toward earth, the light will look compressed to shorter wavelengths. This change is called a blue shift. It is called this because the light moves toward the blue end of the spectrum. By analyzing the spectra of galaxies, astronomers have found out that galaxies move faster when they are farther away from each other. This observation has made astronomers believe that the universe has been expanding throughout its history. As the universe expands the galaxies become farther away from each other. The universe does not expand into anything because there is nothing outside it.
The big bang is the period in time when the universe started to expand out of an extremely hot, dense state. This expansion was very rapid. In one second the universe expanded from a tiny speck of dust to the size of our solar system. Astonomers have calculated and they believe that the big bang happened about fourteen billion years ago. Right after the big bang the universe was extremely dense and hot. It was way hotter than the core of the sun. Some evidence shows that the first stars formed on a couple hundred years after the big bang.
At the end of the letter it said from the “Mystery Man”. I really wanted to know who wrote it because it really taught me a lot.