1. P7: Observing the Universe

2. Convex / Converging Lenses bring light to a Focus

3. Power (dioptre) = 1 / Focal Length
More powerful lenses have more curved surfaces

4. Simple telescopes have 2 converging lenses
Simple telescopes have 2 converging lenses. The most powerful one being the eyepiece lens

5. Magnification = focal length of objective lens / focal length of eyepiece lens

6. Astronomical objects are so distant that light from them is effectively parallel
Light on the outside of this picture is close to parallel, whereas in the centre it is more at an angle

7. Concave Mirror Telescopes
Concave mirrors bring light to a focus
In this telescope, you can think of the concave mirror as being the “objective lens”
Most astronomical telescopes are this type

8. Ray Diagrams Extended off principal axis Label: Source Focal Points
Real Image
Principal Axis
Extended off principal axis

9. Ray Diagrams Extended Source Label: Source Focal Points Real Image
Principal Axis
Extended Source

10. The larger the lens, the sharper the image
Telescope must have a larger aperture than the wavelength of radiation detected to produce a sharp image.
Larger aperture = less diffraction

11. Telescopes on Earth
Major optical and infrared astronomical observatories on Earth are mostly in Chile, Hawaii, Australia and the Canary Islands

12. Astronomical Factors for Telescopes
High altitudes – Less atmosphere above to absorb light
Away from cities – Less light pollution
Good number of clear nights

13. Non-Astronomical Factors
Cost of building observatory
Environmental impact
Social Impact
Working conditions for employees

14. Telescopes in Space Outside Earth’s atmosphere
Avoids absorption (Gamma Rays, X-Rays don’t reach Earth’s surface)
Avoids refraction of light
Very expensive to setup, maintain and repair
Uncertainties of Government funding for space programs (EG: Barack Obama has recently cut funding in this area to concentrate on the economy).

15. International Collaboration
Example:
Gemini Observatory in Chile
Opened 2002
Collaboration between Australia and 6 other countries

16. Advantages to International Collaboration
Cost of manufacturing can be shared
Astronomers from around the world can book time on telescopes in different countries. This allows them to see stars on other sides of the Earth
Pooling of expertise and equipment

17. Direct or Remote Access Telescopes
Astronomers don’t need to travel to each telescope to be able to use it
Can use telescope at convenient times
EG: Schools in the UK can access the Royal Observatory over the internet

18. Computers and Telescopes
Can locate a star and track it across the sky
Image recorded digitally
Computer can enhance image (eg: reduce noise)
Can share images with other scientists quickly
Computers allow hundreds of people from all over the world to access the same telescope

19. Parallax
Close stars seem to move relative to others over the course of the year.

20. Parallax Angle
Half the angle moved against a background of distant stars in 6 months.

21. Parallax Angle Size
A smaller parallax angle means the star is further away.

22. Parsecs
A star whose parallax angle is 1 arcsecond is at a distance of 1 parsec
Calculate distances in parsecs for simple parallax angles expressed as fractions of a second of arc

23. Light Year / Parsec A parsec is similar in magnitude to a light year
1 Parsec = Light Years
Interstellar distances (distance between stars) are a few parsecs (pc)
Intergalactic distances (distance between galaxies) are measured in megaparsecs (Mpc)

24. Intrinsic Brightness (Luminosity)
Total Amount of Radiation the Star Gives Out Per Second
Depends on its Temperature and its Size

25. Observed Brightness
Looking at the night sky, 2 stars may seem to be the same brightness.
However the intrinsically brighter star may be further away.
If you brought the two stars together so that they were the same distance from you, one would stand out as being brighter

26. Cepheid Variables Cepheid variable pulse in brightness.
Their Period relates to their Brightness.

27. Working Out Distances Using Cepheid Variables
Measure the Period
Use the Period to work out Intrinsic Brightness
Measure the Observed Brightness
Compare the Observed Brightness with the Intrinsic Brightness to get the Distance

28. Discovery of Other Stars and Galaxies
Telescopes: Revealed that the Milky Way consists of many stars and led to the realisation that the Sun was a star in the Milky Way galaxy. Also revealed the existance of “fuzzy” objects which originally were named nebulae.
Curtis v Shapely Debate: Were Nebulae objects within the Milky Way galaxy or separate galaxies outside it?
Hubble: Observed Cepheid Variables in one nebula which indicated that it was much further away than any star in the Milky Way, and hence, this nebula was a completely separate galaxy.

30. Solar v Sidereal Day
Sidereal Day 23hrs56mins
Solar Day hours

31. Different stars are seen at different times of the year

32. Planets move in complicated patterns relative to the “fixed” stars

33. Describing the Position of a Star
2 angles form Earth are needed:
Angle from North to the Star.
Angle from the Horizon to the Star.

35. Solar Eclipse: Sun blocked out
Solar Eclipse: Sun blocked out. Rare because the Moon’s orbit is tilted 5 degrees.
Lunar Eclipse: Moon blocked out. More common because the Earth’s shadow is so big.

36. Sun, Stars and Moon
Sun, Stars, Moon (and Planets mostly) move across the sky from East to West. IE: everything sets in the West, not just the Sun. This is explained by the Earth’s rotation.
Sun: 24 hours
Stars: 23 hours 56 minutes
Moon: 25 hours
The Moon takes 28 days to orbit the Earth completely. It also orbits the Earth from West.

37. Hot Objects
All hot objects emit a continuous range of electromagnetic radiation
The greater the Peak Frequency (measured in Hz) the higher the temperature and intrinsic brightness.
Which is why hot blue objects (high frequency) are hotter than a hot red objects (low frequency)

38. Ionisation
Ionisation is the removal of an electron from an atom.

39. Electrons move within Atoms
Electrons can also move between electron shells within an atom
This produces line spectra
Each element has a unique line spectra

40. Star Spectrum
Star spectra contain specific spectral lines. These provide evidence of the elements in the star

41. Rutherford-Geiger-Marsden Experiment

42. Describing the Experiment
Expected Results: alpha particles passing through the plum pudding model of the atom undisturbed.
Observed Results: a small portion of the particles were deflected, indicating a small, concentrated positive charge (the nucleus).

43. The Model of the Atom
Past → Present

44. Structure of the Atom
Saturday, April 22, 2017
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45. The Source of the Sun’s Energy
Up until the mid 19th Century (1850) it was commonly believed that the Sun was composed of some special material that had the ability to shine eternally.
Advancements in the true structure of the atom led to the source of the Sun’s energy.
If you could somehow force the protons present in the nuclei of hydrogen together to form helium nuclei, this would release energy as light and heat.

46. Nebula Nebula are clouds of dust, hydrogen and helium.
These materials "clump" together to form larger clumps.
More mass = more gravity = more mass attracted

47. Protostar
Proto = Prefix meaning “first”

48. Compressed Gases Increased pressure Particles closer together
More collisions with other particles
Friction and collisions between particles increases the temperature

49. Decreased Volume Increased Pressure Increased Temperature

50. Absolute Zero The lowest possible temperature
All particles/atoms stop moving completely
Gas would exert no pressure

51. Two Competing Forces in the Formation of Protostars
Pressure of Compressed Gases
Gravity between the particles of gas

52. Two Competing Forces
Something is holding these smurfs together even though they are trying to pull away from each other

53. Strong Nuclear Force
Something is holding this Nucleus together even though the protons want to pull away from each other.

54. Nuclear Fusion
Hydrogen fusing together to make Helium atoms. This releases lots of energy.

55. Structure of the Sun Core – Fusion takes place
Radiative Zone – Energy transported towards the surface by photons
Convective Zone – Energy transported to surface by convection
Photosphere – Energy is radiated into space

57. When Hydrogen runs out Stars start to change.

58. Average size stars (like out Sun) turn into Red Giants
Massive stars turn into Red Supergiants.

59. Red Giants and Red Super Giants
Higher elements are made by just fusing more Helium nuclei together:
Carbon
Oxygen
Nitrogen
This Fusion process also releases energy
What elements are living organisms made from?
What element has been made in this diagram?

60. Red Giants
Red giants lack the mass to compress the core further at the end of helium fusion.
They then shrink into hot white dwarfs, which gradually cool.

61. Red Super Giants Fusion Continues in Red Supergiants
Due to the high pressure in their core larger elements are formed

62. Red Super Giants
Fusion stops in Red Super Giants when the core is mostly Iron (Fe)

63. Supernova Exlosion
After the core is mostly iron, and fusions stops, a Supernova explosion occurs which ejects much of the star’s materials

64. Neutron Stars and Black Holes
After a Supernova Explosion, the remaining material turns into a Black Hole or Neutron Star
Both of these are extremely dense objects