Here's a few facts I learned (or better said - picked-up) during my long-time fascination with the Universe. I am not an expert in any of this, but I like to acquire information. I also like to share with others what I learned. So, here goes ...
1. Universe is big. Really BIG.
To start thinking about the size of the Universe we don't need to immediately start thinking about billions of light-years to have an idea that Universe is really big. For the start, it's enough to think only about the distance between us and the star that is closest to the Earth.
The closest star to the Earth (outside the Sun) is Proxima Centauri, at 4.22 light-years distance. So, how much is a light-year?
Light moves at speed of 300 000 (three-hundredth thousand) kilometers per second. A light-year is a distance light travels in a year. So, by using some math, we get that one light-year is actually 9.461x1012 km, or better said - 9.461 trillion (nine trillion) kilometers.
Hubble's Shot of Proxima Centauri, our Nearest Neighbour.
Credit: ESA/Hubble & NASA. (source)
The fastest man-made object in history is the Voyager 1 probe, which "as of 2013, was moving with a relative velocity to the Sun of about 17030 m/s" (wikipedia). Even at this speed, it would take Voyager 73.000 years to reach the star closest to us. Remember, it's only 4.22 light-years.
And only our galaxy has a diameter of 100 000 light-years.
Humanity knows that universe is at least 91 billion light-years in Diameter. How? Well, because this is actually the size which we can see with any type of light. We calculated that Universe is 13.8 billion years old. And we also know that universe is expanding. As light travels to us, the universe itself expands. The red-shift in the light enables us to calculate when the light was emitted. So, if light left 13 billion years ago, this distance is now 46 billion light-years in either direction.
This is just the size of the Observable Universe. The total size of the Universe is much bigger and also probably Infinite.
Here's a few videos that help to understand this.
Here's also a more scientific information about how is this distance calculated: Size of the Observable Universe.
2. Universe is expanding
When humanity looks at the night sky, in any direction, we find out that all the galaxies in every direction are moving away from us. Not only this, but the galaxies that are farthest away from us are moving the fastest.
The interesting thing here is that the Galaxies are not moving through space, they are moving because space is also moving. This, simply put, means that universe has no center, as wherever you are in the universe, you see all the galaxies moving away from you. So there are a lot of "centers", which means there is no real center.
It was naturally expected that the gravity would slow down the expansion of the universe. But this is not the case at all. Humans have actually discovered that universe is expanding faster and faster.
It's important to note that this effect is valid on large scales, for example distances between galaxies. At smaller scales, matter is drawn together by the force of gravity, which enables stars to form and our solar system to be held together.
3. You are made by the stars
We are made from stardust. Like Stephen Hawking would say ...
... the Earth and everything around us was made by the stars. Boiling furnaces of hydrogen atoms, like our Sun, made even the atoms in your eyelashes.
- Into the Universe with Stephen Hawking
Almost every element on Earth was formed at the heart of a star. You see, at a star's core, temperature is about 10 million °C which makes hydrogen atoms fuse together and form helium.
How does this happen?
Well, gravity in space compresses hydrogen atoms until they are very close together. Atoms of hydrogen bounce of each other and temperature rises. When 10 million degrees is reached, hydrogen fuses together. This process is called nuclear fusion. When hydrogen fuses - it creates helium.
Here's a video that explains very simply, but very effectively how do stars work.
This process enables stars to use nuclear fusion to make elements up to Iron. When star makes Iron, there's no more pressure to fight off the gravity trying to squish a star.
Now gravity is unchallenged and it pushes the star even closer, which makes it even hotter. But this is only for a moment. At the end star explodes. This is called a Supernova.
The resulting heat from exploding star fuses even the Iron into even heavier elements, like nickel, silver or gold.
Explosion also propels these elements across the Universe and the remains help to create planets, such as Earth.
... so if you have a gold ring, make sure you appreciate it. The metal was made in a blinding flash of light billions of years ago.
- Into the Universe with Stephen Hawking
After Earth was made, it's all about recycling. When a baby grows in a womb, it gets it's atoms and molecules from the food mother eats. When this same baby dies many years later, the body is broken down into simpler elements which then get reused by other plants/animals.
Do not forget. Cells are not atoms. Cells are made of atoms. Atoms come from the Earth and our environment. The food you eat contains the molecules and energy body uses to make new Cells. And all of this came from stars.