1. Earth Science Notes
Stars and Galaxies

2. What is a Star?
A star is a massive, luminous ball of plasma that is held together by gravity.
Stars shines due to nuclear fusion in its core releasing energy that radiates into space.
When stars form they are composed of about 70% hydrogen and 28% helium by mass
There is a small fraction of heavier elements.

3. Classifying Stars
Stars are classified by their luminosity (brightness) and the temperature.
Hetzsprung and Russell developed a graph that shows the relationship between luminosity and temperature.
Three main classification
Main sequence
Dwarfs
Giants

4. The Hertzsprung-Russell Diagram
Classifying Stars
The Hertzsprung-Russell Diagram

5. Classifying Stars
The Hertzsprung-Russell Diagram

7. Classifying Stars Main Sequence Stars
Run diagonally across H-R diagram
Brightness increases as temperature increases
The sun is near the middle of the sequence
Around 90% of all stars are main sequence

8. Classifying Stars Dwarf Stars
White dwarfs – hot but small (bottom-left of H-R diagram)
Red Dwarfs – cool but small (bottom-right of H-R diagram)

9. Classifying Stars Giant Stars
Star with substantially larger radius and luminosity than a main sequence star of the same surface temperature
Some Giants are large but not hot
Super-Giants are even larger

11. Evolution of Stars All stars begin as begin as nebulas
Nebulas – large clouds of gas and dust
As particles in the nebula contract they increase in temperature until the reach 10 million K. This is when fusion begins.
Energy given off from the fusion process powers the star

12. Evolution of Stars Two series for stars
Nebula  high mass star  main sequence  red supergiant  supernova  black hole or neutron star
Nebula  low mass star  main sequence  red giant  white dwarf

13. Evolution of Stars

14. Evolution of Stars Main Sequence to Giant Stars
When hydrogen in a star is depleted, the fusion process begins to stop.
The core collapses and heats up.
The outer layers of the star begin to cool and expand. This stage of the life cycle is called a giant.

15. Evolution of Stars White Dwarfs
When a stars core uses up its fuel it contracts even more and its outer layers escape to space.
This leave behind a hot, dense core
At this stage the stars becomes a white dwarf
White dwarfs are about the size of the Earth. They are dim and hot stars.

16. Evolution of Stars Supergiants
In massive stars, the core heats up to extremely high temperatures and heavier elements form via fusion, the star expands into a supergiant.

17. Evolution of Stars Supernovas
Once an iron core forms the star collapses and a shockwave travels through the star. The outer portion of the star explodes and creates a supernova.

18. Evolution of Stars Neutron Stars
Sometimes when the core of a supernova collapses it will shrink from 3 times the size of the sun to about 20 km. Only neutrons can exist at this density.
One teaspoon of a neutron star is about 600 million metric tons

19. Evolution of Stars Black Holes
Sometimes a supernova’s core can collapse to a point. The gravity at this point is so great that is pulls everything in, even light.

20. Evolution of Stars
Black Holes
                           

21. Evolution of Stars

22. Constellations Constellations are patterns made of stars in the sky
Stars appear close together in the sky, however, they are actually light years from each other

23. Constellations
Some constellations are visible only in the northern or the southern hemisphere
Circumpolar constellations appear to rotate around Polaris (north star)
Some constellations are only visible during certain times of the year

24. Circumpolar Constellations

25. Constellations
Some stars in constellations appear brighter than others.
This can be due to two things:
The stars actual luminosity (brightness)
Actual magnitude – how much light is given off by star
The stars distance
Apparent magnitude – how much light is received on Earth
Stars far away
appear dimmer

26. Constellations

27. Constellations

28. Measurements in Space
Parallax – the apparent change in position of object when viewed from different perspectives

29. Measurements in Space Light year – measurement of distance
The distance light travels in 1 year
9.5 trillion km / year
Astronomical Unit – distance from Earth to Sun = 1 AU
Solar Mass – the mass
of our sun = 1 solar mass

30. Measurements in Space
Wavelengths of light can be measured to determine the composition of stars
Spectra of elements are like fingerprints, they will tell you what elements are present

31. Galaxies and The Universe
Galaxy – large group of stars, gas, and dust held together by gravity
Galaxies are separated
by great distances
millions of light
years

32. Galaxies and The Universe
Our galaxy is the Milky Way
We are located on one of the spiral arms
There is a black hole located at the center

33. The Milky Way

34. Galaxies and The Universe
Three types of Galaxies
Spiral – have spiral arms that swing out from the center (Like Milky Way)

35. Galaxies and The Universe
Elliptical – football shaped

36. Galaxies and The Universe
Irregular – have many different shapes

37. Origin of the Universe Three Models the Universes Origin
The Steady-State Theory
Suggest universe is the same as it has always been
The Oscillating Model
Suggest that the universe expands and contracts over time
The Big Bang Theory
Suggest universe began as an explosion and has expanded ever since

38. Origin of the Universe The Big Bang Theory
Evidence suggest that the universe is expanding. Scientist have theorized that it has expanded from one point
According to this theory the universe began with an enormous explosion

40. Expansion of the Universe
As the universe expands, some stars are moving toward us and some move away. This causes an apparent change in the light we see
Red shift – light moving toward Earth appears more red (toward the red end of the spectrum)
Blue shift - light moving away from Earth appears more blue (toward the blue end of the spectrum)

41. Expansion of the Universe
Redshift and Blueshift

42. Summary Stars are large bodies of plasma held together by gravity
The Hurtzsprung-Russel relates brightness to temperature of stars
There are three main classifications of stars
There are three models for the origin of the universe, the leading model is the big bang theory