Our Place in the Cosmos and Introduction to Astrophysics

1. Our Place in the CosmosandIntroduction to Astrophysics Jon Loveday Astronomy Centre Department of Physics & Astronomy

2. Course Aims To explain primarily at a descriptive level the contents, dimensions and history of the Universe, and our place within it. This will include a survey of the basic astronomical tools, and will seek to explain the way in which some basic physical laws can be applied in order to understand the observed phenomena.

3. Class organisation • Lectures • Monday 9am Arts A5 • Friday 9am Pev1 1A6 • Workshops Friday 10am • Our Place in the Cosmos: Pev1-2A2 • Informal discussion, quizzes, student presentations • Intro to Astrophysics: Arundel 1B • Mathematical background, problem sheets • Taken by Peter Thomas

4. Our Place in the Cosmos 15 minute presentation (weeks 5-10; 20%) In-class quiz (week 10; 20%) 2000-word essay (week 10; 60%) Introduction to Astrophysics 4 x problem sheets (10% each) In-class quiz (week 9; 40%) Briefing paper (week 9; 20%) Assessment

5. Lecturer • Jon Loveday • Pev2 5A5 x 7719 • J.Loveday@sussex.ac.uk • Office hour: Tuesday 1.30-2.30

6. Web Resources • Sussex Direct has links to the official course document (click on the course code: F3095 or F3156) • Study Direct includes copies of these slides and other useful resources

7. Course textbooks • 21st Century Astronomy by Hester et al. is very good, though expensive at £42 • Introductory Astronomy by Holliday is cheaper • Other useful books you should find in the library include: • Universe Freedman & Kaufmann • In Quest of the Universe Kuhn & Koupelis

8. Student Feedback • Please feel free to stop me and ask for clarification at any time during classes if anything I have said is unclear • Feedback on any aspect of the course is welcome during the Friday seminar • Formal feedback will be requested via the Study Direct website during weeks 8-9. Please note that feedback provided in this way is completely anonymous

9. What is Astronomy? • Literally means “naming the stars” • The earliest astronomers simply tracked the motions of the heavenly bodies • Modern astronomers use observations to help understand the Universe and our place within it via scientific reasoning • Astrology is not astronomy, but a pseudo-science

10. Why Astrology is not a Science • The constellations are only imaginary, not physical associations of stars • Constellations have shifted relative to our calendar due to precession of equinoxes since founding of astrology • Rigorous tests of astrological “predictions” have shown they do not work

12. The Scientific Method • Guided by observations, posit a theory that explains them • A good theory makes testable predictions about future observations, and thus is falsifiable • Scientific theories can never be definitively proved, they can only be ruled out by contrary observations • A theory that stands the test of time becomes generally accepted and possibly modified

13. Why Study Astronomy? • Early astronomers used positions of the stars to track the seasons and later as a vital navigational aid • Help understand phenomena such as tides and eclipses • Understand and appreciate even more the beauty of the night sky • Learn about the origin and fate of the Universe

14. Course Outline • Brief tour - scales in the Universe • Historical overview • Earth, Moon and Sun • Orbits and Gravity • Solar System • Stars • Galaxies • The Milky Way • The Universe

15. A brief tour

22. Solar System Sun Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto

23. Milky Way

24. Milky Way as Viewed from Earth NGC 891

25. Milky Way in the near-IR

26. NGC 4414

27. Virgo Galaxy Cluster A cluster of galaxies

28. Infrared Universe

29. The Deep Universe Hubble Ultra-Deep Field

30. CMB Temperature Map

31. Scales in the Universe • Astronomical distances are commonly given in terms of light travel time, ie. distance light will travel in that time at its speed of 300,000 km/s

32. Distances as light travel times - not to scale!

33. Prehistoric astronomy • Since prehistoric times, man has observed the changing phases of the moon during the lunar month, and the changing passage of the Sun during the year • One can understand how, as well as indicating the change of the seasons, man might well have thought of the stars as causing the change • Hence religious significance of the heavenly bodies, and birth of astrology

34. Earliest depictions of the skies are found in the Cave paintings in Lascaux, SW France (c15,000 BC) Dots below horses thought to represent changing phasesof the Moon

35. The Great Bull: An Ice Age Star Map? Pleiades Hyades Orion

36. Prehistoric astronomy • Observations of the changing passage of the Sun and the star patterns in the night sky enabled tracking of the seasons, and hence the best times to plant and harvest crops • Observations of the Moon’s phase allowed fishermen to predict the tides • Observatories were built to track the positions of the heavenly bodies, most famously Stonehenge, 3000-1500 BC

38. Stonehenge • An early astronomical calculator? • On summer solstice, Sun rises exactly above the Heelstone • In Stonehenge Decoded (1965), Gerald Hawkins claimed large number of alignments with Lunar and Solar phenomena, and hence that eclipses could be predicted • These claims are still controversial

39. El Castillo, Chichen Itza (Mayan, c1000 AD) At sunset close to the spring and autumn equinoxes, shadows give the effect of a snake slithering down the stairway.

40. The Planets • It must have been noticed very early that some bodies moved faster in the night sky than the surrounding stars. • The word "planet" comes from the Greek word "planetes," which means "nomad” or “wanderer”. • To the Babylonians and Sumerians before them, the planets were "stray sheep”.

41. The Ancient Greeks By far the most famous early astronomers are the ancient Greeks. Between about 500BC and 100BC, they built a picture of the Universe which dominated for over 1000 years.

42. Thales (624 - 545 BC) Realised that celestial objects were at different distances, that the Earth was spherical, and that the light of the moon was reflected sunlight. Pythagoras (582 - 500 BC) Produced the first geocentric model of the Universe, with everything making perfectly circular orbits around the Earth.

43. Geocentric Model