1. From small to big scales
- Cosmology II
„Cosmology is the study of the origin, evolution, and eventual fate of the Universe.“

2. The Solar system
The Planets were all created in the same disc of gas around the Sun, when a big gas cloud collapsed forming the solar system including the Sun.

3. The Interior of Stars
By mass 75 % of the Universe is composed of Hydrogen and so are stars.
In the stellar centre the temperature is high enough for fusion processes to take place.
These fusion processes make stars shine. Furthermore, all elements heavier than Lithiium are produced in stars, so we are all made of star stuff, the remains of stars that died billions of year ago.

4. Stellar fusion
In its current state, the Sun produces Helium. When there is no Hydrogen left in the core, the Sun becomes a red giant and produces heavier elements. Then it will become a white dwarf... Basically a big ball of Carbon that may explode at some point.
The planetary nebula may contract again making a ne stellar system.

5. There are Different Kinds of Stars
Bigger stars are hotter, bluer and die earlier.
Stars form Clusters and Galaxies

6. Page 29
You see a sketch of the galaxy on page 29. The distance is given in parsec (pc). 1 pc = 3.26 ly.
How many meters is 1 ly?
Proxima Cenaturi is the closest other star 4.2 ly away. How many AU is that? How many pc?
Make exercise 3 and 8 in the book.

7. Galaxies Form Clusters
The galaxies near the Milkyway are gravitationally bound in the Local Group

8. The cosmological principle: Viewed on a sufficiently large scale, the properties of the universe are the same for all observers. It is homogeneous and isotropic.

9. Hubble‘s Law
The Universe is currently expading. The speed, v, depends on the distance d: v = H0d, where H is Hubble‘s konstant, normally given in km/s/Mpc.

10. Dark Energy
The Universe is currently expanding at accelerating speed. Something must be pushing everything appart. This something is dark energy: 74 % of the energy density of the univers. 22 % are so-called dark matter. Only 4 % are known stuff (atoms).

11. The Big Bang
At the beginning of time and space the Universe was in a dense state, i.e. the energy density was very high. Quarks and other fundamental particles were constantly created and destroyed. The Universe expanded and cooled, and the quarks formed protons and neutrons. At this point the Universe was a billionth of a second old.

12. Big Bang Nucleosynthesis
The Universe kept cooling, as it expanded. After a few minutes the neutrons formed deuterium that formed Helium via fusion. The Universe was now 25 % Helium by mass. The rest was mainly Hydrogen. This is still the case today, alltough stars forge heavier elements.

13. The CMB
After years the Universe was so cool that atoms were formed. As the Universe stopped beeing a plasma made of charged particles, background radiation was released. We see that still today: CMB (Cosmic Microwave Background).