P7 - Observing the Universe Subtopic 1 Telescopes

1. P7 - Observing the UniverseSubtopic 1Telescopes

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. 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 • Label: • Source • Focal Points • Real Image • Principal Axis • Extended off principal axis

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

10. The larger the lens, the sharper the image • Telescope must have a larger aperturethan 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 • Remote access • 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. Subtopic 2The Night Sky

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

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

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

23. 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

24. Light Year / Parsec • A parsec is similar in magnitude to a light year • 1 Parsec = 3.26163626 Light Years • Interstellar distances (distance between stars) are a few parsecs (pc) • Intergalactic distances (distance between galaxies) are measured in megaparsecs (Mpc)

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

26. 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

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

28. 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

29. 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.

31. Solar v Sidereal Day • Sidereal Day 23hrs56mins • Solar Day 24 hours

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

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

34. 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.

36. 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.

37. 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.

38. Subtopic 3Stars

39. 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)

40. Ionisation • Ionisation is the removal of an electron from an atom.

41. 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

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

43. Rutherford-Geiger-Marsden Experiment

44. 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).

45. The Model of the Atom Past → Present

46. Structure of the Atom Page 34 - 35

47. 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.

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

49. Protostar • Proto = Prefix meaning “first”

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