1. Theme 4 – Galileo ASTR 101 Prof. Dave Hanes

2. The First Real Experimentalist Explored dynamics – forces and motions Studied balls rolling on slopes and planes Recognized the importance of friction and air resistance All falling objects behave in the same way. (Tower of Pisa?) http://www.youtube.com/watch?v=5C5_dOEyAfk

3. All Motion is Relative The Galilean relativity principle Is the weight falling straight down, or along a curved path? It depends: are you on shore, or on board? Lesson: The behaviour of stones tossed in the air can’t tell us if the Earth is moving or not (an ancient argument). http://www.astro.queensu.ca/~hanes/ASTR101-Fall2015/ANIMS/GalRel.mp4

4. Inertia! His reasoning: His misunderstanding:

5. The Human Eye Its Function and Limitations

6. Light Refracts (Changes Direction) as it Moves from One Medium to Another - so lenses can focus light

7. The Basic Steps Light enters the pupil enters the pupil is refracted and focussed by the lens is refracted and focussed by the lens to form an image on the retina. to form an image on the retina. The energy of the light has a chemical effect on the pigments (enzymes) in the receptor cells that make up the retina, and has a chemical effect on the pigments (enzymes) in the receptor cells that make up the retina, and an electrical signal is sent along the optic nerve to the brain. an electrical signal is sent along the optic nerve to the brain. The brain does the rest!

8. Some Important Concepts 1. Dynamic Range (day vs night) How it’s achieved (in part): the pupil expands! in dim lightvs in bright light Much more important: the replenishment of the pigments – hence, we get dark-adapted.

9. 2. Accommodation [focussing our eyes] We lose this ability as we age – hence, reading glasses.

10. 3. Persistence of Vision Allows us to watch movies, TV, etc. http://www.astro.queensu.ca/~hanes/ASTR101-Fall2015/ANIMS/Persist.mp4

11. 4. Colour Vision 4. Colour Vision To discriminate colours, we need at least two different kinds of receptors with different enzymes, having different sensitivities. Our retinas contain rods and cones.

12. The Difference

13. One Implication, and One Puzzle 1. The implication: When it’s dark, there is too little light to stimulate the Cones, so everything looks shades of black and white at night. With rare (bright) exceptions, the stars look colourless! (But have you ever noticed the subtle ‘redness’ of Betelgeuse, Antares, and Mars?) 2. The puzzle: If our Cones are sensitive to red, green and blue, why do some things look yellow, orange or purple?

14. The Puzzle Answered Together, red light and green light give us the sensation of yellow! Similarly, green and blue sensation of yellow! Similarly, green and blue yield teal; red and blue produce magenta. (All three mixed together produce white.) The light from a yellow object stimulates both the red and green receptors to some extent – and we see yellow. http://www.astro.queensu.ca/~hanes/ASTR101-Fall2015/ANIMS/RGB-Col.mp4 That is how old colour televisions work: electrons stimulate various tiny spots on the screen to glow red, green or blue – in combination, this generates all colours. http://www.youtube.com/watch?v=xzmXrC-Yzfc&feature=related

15. 5. Resolution How much detail can you discern?

16. Finer Grain yields Better Resolution How many pixels, or How many pixels, or “picture elements,” are there? My camera has 12 megapixels. In your eye: 125 million rods and cones! (But they are clumped in groups, so not really quite that many in effect.)

17. The Size of the Image Also Matters If two photons (‘lumps’of light) arrive at well-separated spots on the retina, landing on different ‘pixels,’ they can be seen to be coming from two separate objects. But two photons that arrive closely side by side can’t be distinguished (the details are “unresolved”).

18. Example: To the Unaided Eye, Saturn is Just a Point of Light Its image formed on the retina is tiny – just a dot! To see details, either: Move closer to the target Move closer to the target so that it looks bigger (that is, the image is spread over a larger area on the retina) Or use a telescope to magnify the image. Or use a telescope to magnify the image.

19. Galileo’s Telescope Not invented by Galileo, but he saw its potential for astronomy.

20. Four Important Discoveries – Interesting but Not Definitive 1. Features on the moon 2. Sunspots and their motions 3. ‘Extensions’ on Saturn 4. Stars in the Milky Way

21. 1. The Moon

22. Galileo’s Interpretations 1. Maria! (seas, like the Mediterranean) 2. Mountains! Imperfection!

23. Galileo’s Calculations peaks of mountains lit by the setting Sun

24. 2. Sunspots that Move they go once around every ~25 days or so The sun can clearly spin without flying to pieces! So the Earth can too… http://www.astro.queensu.ca/~hanes/ASTR101-Fall2015/ANIMS/SSpots.mp4

25. 3. Saturn’s ‘Extensions’ with a modern picture at the bottom 3. Saturn’s ‘Extensions’ with a modern picture at the bottom

26. The Vanishing Rings they are very thin!

27. 4. The Milky Way Resolved: Stars! we may be far from unique

28. Plus Two Critical Discoveries Jupiter has moons that orbit it Jupiter has moons that orbit it Venus displays a full range of phases Venus displays a full range of phases (from new to crescent to full and back) (from new to crescent to full and back)

29. The Moving Moons of Jupiter as sketched by Galileo They orbit Jupiter and ‘keep up’ with it as it moves Presumably our Moon can keep up with us!

30. Modern Images they are comparable to our Moon

31. 2. The Phases of Venus A prediction from Ptolemy’s model: Since Venus is always between us and the Sun, we should never see the face of Venus fully lit up (just crescents)

32. But If Copernicus is Right Venus goes around to the far side of the Sun. So, from the Earth, Venus should appear full (and small!) at those times.

33. Monitor it for ~18 Months Why not use your Starry Night-sky simulation software to find Venus and monitor its appearance as the months pass? That’s shown here: http://www.astro.queensu.ca/~hanes/ASTR101-Fall2015/ANIMS/VPhases.mp4 and in this series of still photos: Copernicus was right!

34. Full Venus

35. Guilty of Heresy, Sentenced to House Arrest ”Wine is light held together by moisture.” – G Galileo

36. One Bizarre Relic