Galileo

1. Galileo What did he know then? What would he think now? Judith Irwin, IYA Kickoff, Jan 10/09

2. In 1564, two individuals were born in different countries. The influence of one would transform the literary world. And the influence of the other would transform the scientific world. William Shakespeare Galileo Galilei

3. Galileo Galilei b. Feb 15, 1564, Pisa d. Jan 8, 1642, Arcetri Father Vincenzo a musician of some success -- an experimentalist with music who was well known, though not wealthy. He wrote several books and distrusted authority. He taught Galileo to play the lute which Galileo enjoyed throughout his life. Galileo was the oldest of 7 children and was expected to take care of them, if need be. 1606, Padua, 42 years old

4. Natural philosophy, circa 1600 The Earth is at rest at the center of the universe. The Earth is fundamentally different from all other heavenly bodies. Heavenly bodies and the space between them are ‘perfect’ and ‘eternal’. The Earth is ‘corruptible’ and ‘changeable’. A perfect body is an absolutely smooth sphere moving in a circular path. This was the prevailing view for almost 2000 years. Aristotle -- 384 - 322 B.C.

5. The Aristotelian view translated into the ‘Ptolemaic system’ Ptolemy (85 - 165) The Almagest (`The Great Treatise’)

6. A retrograde loop of Jupiter and Saturn ‘Saving the appearances’

7. The Polish astronomer, Nicolaus Copernicus Jupiter Earth 7 6 Sun 5 4 3 2 1 The earth is just like the other planets, revolving about the sun. Copernicus (1473 - 1543) De Revolutionibus Orbium Coelestium (`On the Revolutions of the Heavenly Spheres’ - handed to him on his deathbed)

8. The ‘spyglass’. Autumn 1608 -- 3 applications for patents on a device that could make distant objects appear closer were filed in the Netherlands. They were rejected because the device was considered to be too easy to copy. By the spring of 1609, eyeglass makers were offering small `spyglasses’ in shops in Paris. The magnification was 3 to 4 times. Galileo first heard about the spyglass around May of 1609 and thought that he might be able to improve upon the instrument. Patent application of Hans Lipperhey of Middleberg, Oct. 2, 1608 to patent office of the Netherlands

9. Galileo’s Telescopes First constructed in June or July, 1609 He needed lenses that were not commercially available, so taught himself to grind and polish his own lenses. Presented 8 X instrument to Venetian senate in August, 1609 By Oct. or Nov., he had constructed a 20 x instrument, far superior than the others that were in circulation. Field of View: 15 arcmin Focal length: 30 - 40 inches Magnification: 20 times

10. Galileo’s Publications The Little Balance (1586) age 22 On Motion (1590) Mechanics (circa 1600) On the operation of a geometrical and military compass (1606) The Starry Messenger (Sidereus Nuncius) (1610) age 46 Letter on sunspots (1613) Discourse on the Tides (1616) Discourse on the Comets (1619, under his student’s name) The Assayer (Il Saggiatore) (1623) Dialogue concerning the Two Chief World Systems*(1632) age 68 Letter to the Grand Duchess Christina (1636) Discourse … on Two New Sciences (1638) *Dialogue between Salviati, Sagredo, and Simplicio

11. First target --The Moon Look how bright the moon is -- it is like a brilliant jewel in the sky -- it is fundamentally different than the Earth which is rough and dark. The moon just looks bright because of the contrast between it and the surrounding dark sky. In the daytime sky it is no brighter than a cloud.

12. The moon must be perfectly smooth like a mirror in order to reflect the light of the sun so well. On the contrary. If the moon’s surface were like a mirror, it would appear dark to us. A rough surface is needed for us to see reflected light. Watch the mirror on the wall!

13. We can sometimes see the ‘secondary’ light from the dark part of the moon. So the moon emits its own light and is therefore different from the earth. The dark side is most easily seen when the moon is a thin crescent against a brighter sky. After its 1st quarter phase when the moon is seen in a darker sky, the dark side can barely be seen. What we are seeing is light from the earth reflecting onto the moon. The earth would actually look bright, just like the moon does to us, if seen from space.

14. Besides, through my telescope, you can actually see mountains and circular valleys on the surface of the moon. It is clear that the moon is not a perfect sphere but has a rough surface. The surface is perfectly smooth, but light is reflecting from within the sphere, like an opal. This can’t be the case because the boundary between light and dark is irregular in such a fashion that shadows are cast. Furthermore, the shadows virtually disappear at full moon when the sun shines directly on it.

15. The Milky Way and clusters “What was observed by us … is the nature and matter of the Milky Way itself, which, with the aid of the spyglass … an immense number of stars immediately offer themselves to view, of which … the multitude of [faint] ones is truly unfathomable.” Sdereus Nuncius

16. 15 arcmin field of view

17. Next target -- Jupiter January 7, 1610 Hmm.. There are 3 background stars near Jupiter. Curious that they’re all in a row. January 8, 1610 What? These 3 stars have shifted to the west. But how can that be? Jupiter’s motion is retrograde so they should be on the east side. Could the tables be wrong and Jupiter is really prograde after all? January 9, 1610 -- Cloudy! Aargh! January 10, 1610 These new stars are moving *with* and seemingly about Jupiter. The 3rd must now be behind its disk..

18. Galileo soon found a fourth ‘star’ which was further out and continued to track and measure the angular separations of the 4 stars into March of 1610. Galileo named what we now call the Galilean satellites of Jupiter, the ‘Medicean stars’, dedicated to the Grand Duke Cosimo de’ Medici. The 4 stars orbited Jupiter and moved along with that planet. The Earth is not at the center of the universe!

19. What you are seeing is nothing more than flaws in the optics of your telescope. I will give a large sum of money to the first person who can build a telescope that puts moons around Jupiter and not around any other planet. The astrologers have already taken into account everything that could have influence on man. Since nature does nothing in vain, the new stars could serve no purpose and therefore could not exist. The new stars certainly do serve a purpose and that is to torment ignorant naysayers and throw superstition into confusion!

20. The Sun In 1611, Galileo observed the sun by projecting its image on paper and discovered sunspots. (Johann Fabricius of Wittenberg & Thomas Harriot in England) The sun is blemished. Heavenly bodies are not perfect! He went much further -- from observations of sunspots that are long lived, Galileo found that the sun “completes an entire revolution in about one lunar month”.First letter on sunspots from Galileo Galileo to Mark Welser “There is no longer any room for doubt that the sun revolves.” Third letter on sunspots from Galileo Galileo to Mark Welser

21. His observations showed that sunspots lasted from 2 to 40 days and that they mostly fell within 29 degrees of the sun’s equator. All you are seeing is little clusters of planetary spheres passing between us and the sun’s face. No, they must be ‘attached’ to the surface because the cluster moves together (not separately as would planets), they are foreshortened at the edge, and they sometimes form near the *center* of the sun -- a planet would appear at the edge first.

22. Venus “… discovered by me about two years ago and communicated to so many people that by now it has become notorious. That is the fact that Venus changes shape precisely as does the moon.” First letter on sunspots to Mark Welser, May 4, 1612

23. Galileo also found that all the other planets also show changes in their size consistent with orbits about the sun. If they orbited the earth in circles, their disks would not change size over time. “Venus revolves about the sun just as do all the other planets.” First letter on sunspots to Mark Welser May 4, 1612

24. This still left open the possibility of a solar system such as had been proposed by the Danish astronomer, Tycho Brahe. Tycho Brahe (1546 - 1601) Does the earth move?

25. The Rotation of the Earth If the earth rotated, all of the birds would be left behind. And if you shot up a cannonball, it should land far to the west of you if the earth turned towards the east. And you should continually feel a strong east wind. Entire cities would whirl into the sky. West East

26. Experiments show that these things are not true. When a rock is dropped from the top of the mast of a large ship, it falls in exactly the same place at the foot of the mast *even if the ship is moving*. The rock starts with the motion of the ship and if you stand on the deck, you couldn’t tell from the rock whether the ship is moving or not. Likewise, the birds take off into the sky already having the motion of the earth’s surface. We can’t actually tell whether or not the earth rotates from our position on its surface!

27. If the stars turned about the earth, they are so far away that their speed would be inconceivably high. But we already know from my observations of the motions of Jupiter’s moons that the most distant ones move the slowest -- not the fastest. “I should think that anyone who considered it more reasonable for the whole universe to move in order to let the earth remain fixed would be more irrational than one who should climb to the top of your cupola just to get a view of the city and its environs, and then demand that the whole countryside should revolve around him so that he would not have to take the trouble to turn his head.” --- Salviati, in Dialogue Concerning Two Chief World Systems

28. It was 1851 before the earth’s rotation could be demonstrated dynamically. The foucault pendulum -- Jean Bernard Leon Foucault Foucault pendulum (67 m wire) in the Pantheon in Paris. A foucault pendulum rotates 2pi sin(phi) clockwise degrees per sidereal day

29. The Orbit of the Earth Common sense and the writings of the ancients dictate that the earth is motionless at the center of the universe. As with rotation, we can’t tell that the earth is motionless from our position on it. In fact, the Copernican system is simplest and explains all of the observations. Consider the arguments …

30. Jupiter Earth 7 6 Sun 5 4 3 2 1 All the other planets orbit the sun. The earth is more like the planets than the stars since it doesn’t shine by its own light. The retrograde loops of the planets, as we have already seen, can be explained by the outer planets moving more slowly than the inner planets.

31. The change in the sun’s angle between winter and summer can easily be explained by the earth’s annual motion around the sun together with the tilt of the earth’s axis at 23 1/2 degrees.

32. The annual motion of the sun through the zodiac is easily accounted for.

33. Galileo found that the sun’s axis was tilted about 7.5 degrees from the ecliptic NP. His careful observations showed that the sunspots made arcs that differed 6 months apart. NP SP

34. If earth is moving why don’t we see the stars in different places over the year? The stars are just too far away to make this measurement yet. “It would be a good thing to investigate with the greatest possible precision whether one could really observe such a variation as ought to be perceived in the fixed stars, assuming an annual motion of the earth.” Dec Jun Sun The first successful parallax measurements were made (Bessel) in 1838.

35. What would he think now? (Planning stage)

37. Europa Io Callisto Ganymede

39. ‘Earth rise’

40. “I do not feel obliged to believe that the same God who has endowed us with sense, reason, and intellect has intended us to forego their use.” “We must take care that no passion -- either toward others or ourselves -- bends us away from our aim of pure truth.”