P7 2

P7 2

Parralax
1. Things appear to move when you are moving
2. We can work out the distance to stars that are close with parallax using trigonometry
3. We can do this as we know the distance from the earth to the sun
4. The bigger the parallax angle the closer the star
5. 1 degree = 60 minutes
6. 1 minute = 60 seconds
7. Closest star is 0.76 seconds parallax angle
8. Seconds written as 6"
9. Minutes written as 6'
10. Parallax doesnt work for stars really far away
11. 1 Parsec = distance of object with parallax angle of 1 second
12. Distance in parsecs = 1/parallax angle seconds
Hudgens method
1. The further away a star the fainter the light
2. Light gets weaker with distance as the photons spread out
3. Problems
  1. 1. Some stars naturally brighter and bigger
  2. 2. He wasnt taking measurements
  3. 3. He was assuming all stars are the same
4. Luminosity = how bright a star actually is
5. Luminosity = energy given out per second as light radiation
6. Luminosity depends on how hot and big a star is
7. Observed brightness is how bright it appears to be from earth
  1. Depends on - Stars luminosity - Distance from earth - Dust or gas blocking it
8. A cepheid is a star that varies in its brightness
9. By measuring a cepheids period you can work out the luminosity and the distances very quickly
10. Correlation between luminosity and period length in a cepheid
11. So people can find out the distances and luminosity of stars with cepheids
Hubble
1. Shapleys argument
  1. 1. Universe is a gigantic galaxy
  2. 2. Sun and solar system are far off the center of the universe
  3. 3. Nebulae are huge clouds of dust and are part of the milky way
2. Curtis's argument
  1. 1. Universe is made up of many galaxies
  2. 2. Our galaxy is smaller than shapley suggests
  3. 3. Spiral nebulae are the other distant galaxies completely separate form the milky way
3. Hubbles conclusion
  1. 1. Shapley was right that the solar system is far from the center of the universe
  2. 2. Curtis was right about the nebulae, they are far away in separate galaxies
4. He did this using cepheids to see how far away they are
5. 1 mega parsec = 1 million parsecs
6. Hubble used the cepheid technique to determine the distances of other galaxies
7. By red shift he also found that the galaxies are moving away from us
8. A spectrometer is a device that splits light into all the colours produced by the star
9. All stars contain hydrogen
10. A spectra from stars has black lines because different elements absorb particular wavelengths of light
11. The black lines for hydrogen are in every star
12. If the black lines are shifted slightly to t he left towards red) then they are moving away
13. The further away the galaxies the faster they are moving away from us
14. Hubble compared red shift of galaxies and how far away they are and it was basically directly proportional
15. Speed of recession = Hubble constant x distance
16. km/s = km/s per Mpc x Mpc
17. Hubble constant = 70.6 km/s per Mpc
Understanding stars
1. Stars are not all the same colour
2. The colour depends on how hot it - the hotter the more white-blue - the colder the more red
3. The peak of the graph shows the actual colour and heat of the star
4. The more to the left the peak is the hotter the star as it releases radiation at a higher frequency
5. The higher the peak the more luminous it is as it releases more radiation
6. The frequency is increasing as it gets more to the left (opposite x axis)
Emitting and absorbing photons
1. When you put the light of the sun through a spectrometer there are lots of black Fraunhofer lines
2. Some wavelengths are missing
3. Burning different elements give different colour flames
4. Different elements give out different wavelengths of light when heated - eg sodium gives out two of yellow
5. The wavelengths that is emits is called an elements emission spectra
6. No two emission spectra are the same
7. The emission spectra is the same as the elements absorption spectra
8. You can look at the spectra from a star and see which elements are present
9. Helium was discovered using this
10. Basically when an atom gives out or absorbs light the electrons are moving up or down energy levels
11. When an electron absorbs light it goes up an energy level
12. When it emits light it goes down an energy level
13. The amount of energy a photon has depends on the difference between energy levels occupied by the electron
14. The energy levels are arbituary mathematical values
15. Different elements have energy levels in different places
16. Different jumps of energy levels mean a different wavelength of light it emitted
17. Electrons will only absorb photons with the exact energy to get it up an energy level
18. There are as many Fraunhofer lines (black lines) as there are combinations of different energy levels jumps
How stars and solar systems form
1. Scientist believe all stars were formed by clouds of gas slowly being brought together by gravity
2. After a long time when the gas starts to get close together it starts spinning
3. As it spins around the temperature increases
4. As everything collapses the particles spin around faster and it gets hotter
5. Eventually, it will get hot enough to fuse hydrogens and then it will be classified as a star
6. Over time some of the mass/gas doesn't make it to the star - they are left outside and form planets and mooons
7. A protostar is a star that isn't hot enough for fusion
8. When it starts fusing hydrogen it is a main sequence star
9. Differences between stars is due to their masses

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