Astro 201: Aug. 26, 2010

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1 Astro 201: Aug. 26, 2010 Turn in HW #1 in front of room Pick up Telescope Lab Handout Reading: Hester et al: Chapter 2 Gleiser: Chapters 1-6 Wait List students have been added; class limit will be increased, so everyone can be enrolled Today: Discuss Telescope Lab, On- Line quiz History of cosmology and the scienqfic method On- line Quiz, go to d2l: Open book, 10 quesqons, available ater class today, do it before class next Thursday Which of the following is the largest? a. the diameter of the Moon b. the diameter of Earth c. the diameter of the Milky Way d. the diameter of the Sun e. 1 astronomical unit 1

2 Cosmology: Some History Lascaux Cave PainQngs: Cro- Magnons recorded the lunar cycle 15,000 years ago hyp://news.bbc.co.uk/2/hi/science/nature/ stm 2

PATTERNS IN THE SKY Ancient peoples observed the Sun and stars and created calendars that marked the yearly passage of Qme Earth rotates on its axis once every 24

3 PATTERNS IN THE SKY Ancient peoples observed the Sun and stars and created calendars that marked the yearly passage of Qme Earth rotates on its axis once every 24 hours Earth revolves around the Sun once every 365 days The stars appear to rise in the east and set in the west every night, on a big dome called the celes*al sphere. 3

west. Circumpolar Stars Always above Horizon In the Northern Hemisphere, they Appear to

4 The Earth's rotaqon is counter clockwise looking down on the N pole, and results in the apparent moqon of the celesqal sphere - - everything rises in the East and sets in the west. Circumpolar Stars Always above Horizon In the Northern Hemisphere, they Appear to rotate around The North Star, Polaris In the Southern Hemisphere, No bright star at rotaqon center 4

in any parqcular constellaqon are at different distances

5 CelesQal Sphere and ConstellaQons The sky is divided into 88 "official" constellaqons, although in reality the stars in any parqcular constellaqon are at different distances from Earth. Figure 2.3: The celesqal sphere as a useful ficqon 5

6 8/26/10 Figure 2.4: As viewed from the Earth s North Pole Figure 2.5: Our perspecqve on the sky depends on our locaqon 6

7 8/26/10 Figure 2.9, Right: CelesQal sphere at diﬀerent laqtudes Figure 2.10: Earth s orbit and constellaqons along the eclipqc The Zodiac 7

Rise and set of the Sun and Stars has 2 possible explanaqons GEOCENTRIC Earth at the center Sun and Stars go around the Earth once per day HELIOCENTRIC Earth rotates on its

8 Rise and set of the Sun and Stars has 2 possible explanaqons GEOCENTRIC Earth at the center Sun and Stars go around the Earth once per day HELIOCENTRIC Earth rotates on its axis and so the Sun and stars appear to go around the Earth Ancient EgypQan celesqal sphere: the goddess Nut ( noot ) c BC Nut gave birth to the Sun god RA every morning 8

vault in the midst of the waters, and let it divide water from water.

9 Hindu Rig Veda (1500 BC) WriYen cosmology (Sanskrit) Cyclical or recursive universe Universe originates from the Hiranyagarbha, or golden egg Timescales eerily coincident with modern results, e.g. age of the Earth Hebrew Cosmology And God said, Let there be a vault in the midst of the waters, and let it divide water from water. And God made the vault and it divided the water beneath the vault from the water above the vault, and so it was. - Genesis 1:6 Michaelangelo s depicqon of the creaqon Of the planets and stars 9

Biblical Qmes was understood to be firm only by the will of God.

10 God had divided the waters "above" from the waters "below" by construcqng an immense dome that held open the space for dry land. In the Hebrew Bible the dome is called "raqi'a," meaning a firm substance, and rendered in the King James translaqon as "the firmament The firmament in Biblical Qmes was understood to be firm only by the will of God. If God were angered, "the windows of heaven" and "the fountains of the deep could burst open once again and those lovely blue waters would destroy the Earth. A painqng by the American Edward Hicks ( ), showing the animals boarding Noah's Ark two by two. 10

to center of Earth, compressing the Earth into as compact a shape

11 Aristotle 4 th century BC, Greece First to give reasons why the Earth is spherical Aristotle s 1 st reason: Gravity pulls mayer to center of Earth, compressing the Earth into as compact a shape as possible. a sphere Thanks to Barbara Ryden for this discussion 11

12 2 nd reason: You see different stars from the south than from the north. Big Dipper Southern Cross If the Earth were flat: Big Dipper Southern Cross 12

Earth rotates on its axis & goes around the Sun.

13 3 rd reason: The shape of the Earth s shadow. Another Greek: Aristarchus of Samos 3 rd century BC Proposed that the Earth rotates on its axis & goes around the Sun. Rejected by contemporaries He used geometry to esqmate the size of the Sun and Moon, and their relaqve distances 13

14 What was his reasoning? The Sun is farther away than the Moon because the Moon comes between the Sun and the Earth during a solar eclipse. ANIMATION The phases of the Moon result from the Moon orbiqng the Earth ANOTHER ANIMATION 14

15 Aristarchus measured the angle between the Moon and the Sun when the Moon was half lit, and deduced the raqo of the Sun- Earth distance to the Moon- Earth distance. Here s a picture more to scale M E S Thus, Aristarchus correctly discovered that the Sun is much farther away from the Earth than the Moon. He then concluded that the Sun was MUCH bigger than the Earth or Moon. He reasoned that it was more plausible that the smaller body would orbit the bigger body: thus the Earth orbits the Sun 15

Planets and the Sun are between the EARTH and STARS PTOLEMY 2 nd century AD

16 Despite Aristarchus, for 2000 years, a GEOCENTRIC model of the Universe was favored EARTH at the center STARS affixed to the celesqal sphere Moon, Planets and the Sun are between the EARTH and STARS PTOLEMY 2 nd century AD Ptolemy s ALMAGEST was translated into LaQn in 1496 GEOCENTRIC: Earth at center 16

Copernicus (1473-1543) Heliocentric Model Ptolemy s Epicycles In order to understand the moqon of the planets in the sky Ptolemy s model had to be modified In

17 Copernicus ( ) Heliocentric Model Ptolemy s Epicycles In order to understand the moqon of the planets in the sky Ptolemy s model had to be modified In terms of the heliocentric model, the planets orbit the Sun in ellipses, not circles Retrograde moqon of the planets with respect to the stars required EPICYCLES 17

EclipQc the fact that the planets orbit the Sun in a plane means that they always appear to lie on a great circle on the sky, called the eclip*c Retrograde moqon The planets someqmes appear to be

18 EclipQc the fact that the planets orbit the Sun in a plane means that they always appear to lie on a great circle on the sky, called the eclip*c Retrograde moqon The planets someqmes appear to be traveling west to east, unlike the stars and Sun which always go east to west Next slide: animaqon Astronomy Picture of the Day for Dec. 20, Jupiter and Saturn showing retrograde moqon. Combining 23 pictures taken at 2 week intervals from June May Planet = wanderer 18

19 Ptolemy s explanaqon for retrograde moqon of the planets 19

20 Earth Off Center Earth Equant Epicycle Deferent The planet moves along its epicycle as the epicycle moves along the deferent around the Earth. To make the observaqons as accurate as possible, it was necessary to place the Earth slightly off center of the orbits, but to preserve symmetry that meant that there was an equal place ( Equant ) opposite the Earth from the center. The combined moqon of the planet and the resulqng retrograde moqon are shown. 20

21 Copernicus explanaqon for retrograde moqon Copernicus: On the RevoluQon of the Heavenly Spheres Published at the Qme of his death, in 1543 Major Conclusions: 1. The planets orbit the Sun 2. The apparent daily moqon of the Sun and stars is the result of the Earth s rotaqon 3. The stars are much farther away than the Sun 21

22 Heliocentric model: distance from Sun to stars must be much greater than distance from Sun to Earth. Since Earth orbits Sun, stars should show parallax (a shio in apparent posipon) over the course of half a year. OBSERVATION: Parallax of stars is TOO SMALL to be seen by the naked eye. Not observed unql 1800s. ImplicaPon: distance to stars is several thousand Qmes Earth Sun distance. 22

Parallax Unit of distance: the PARSEC A star which is one parsec from Earth shows a parallax of one arcsecond d = 1 p Remember: 360 degrees in a circle, 60 arcminutes per degree, 60 arcseconds

" It stayed on this list of prohibited books and teachings unql 1822.

23 Parallax Unit of distance: the PARSEC A star which is one parsec from Earth shows a parallax of one arcsecond d = 1 p Remember: 360 degrees in a circle, 60 arcminutes per degree, 60 arcseconds per arcminute ReacQons to Copernicus: On March 5, 1616, Copernicus' work was banned from being taught and discussed by the CongregaQon of the Index "unql corrected." It stayed on this list of prohibited books and teachings unql MarPn Luther ( ): [Copernicus] is a fool who wishes to reverse the enqre scheme of astronomy; but sacred scripture tells us that Joshua commanded the Earth to stand sqll, not the Sun. Giordano Bruno ( ): burned at the stake for advocaqng that stars are suns in their own right, and that there is a plurality of worlds like the Earth. 23

24 Cosmological Models: Version 1.0: Superdome model v. 1.0 Version 2.0: Geocentric model v. 2.0 Version 3.0: Heliocentric model v. 3.0 Which is right? Occam's Razor: Pluralitas non est ponenda sine neccesitate "plurality should not be posited without necessity." Given a set of otherwise equivalent models of a phenomenon, the simplest one is the best. Keep it simple, stupid. 24

William of Occam 1285-1349 English philosopher from Ockham Franciscan Monk Got into trouble with the Pope

c.f. Ontological parsimony Epistomology = theory of knowledge Ontology = what exists?

Starry Messenger) Spots on the Sun; the Sun rotates The Moon has mountains, craters, rocky surface with

25 William of Occam English philosopher from Ockham Franciscan Monk Got into trouble with the Pope for advocaqng apostolic poverty Died of the Black Death while in exile Advocated Epistomological Parsimony c.f. Ontological parsimony Epistomology = theory of knowledge Ontology = what exists? Galileo Galilei ( ) Italian First to use a telescope to look at the sky 1610 Siderius Nuncius (The Starry Messenger) Spots on the Sun; the Sun rotates The Moon has mountains, craters, rocky surface with imperfecqons The planet Jupiter is not a pinpoint star but a disc in the sky WITH MOONS that orbit it Venus has PHASES like the MOON 25

26 Galileo Galilei ( ) Spots on the Sun The Sun rotates Eventually went blind Galileo Galilei ( ) The Moon Has Mountains and Valleys 26

Galileo Galilei (1564 1642) Phases of Venus Galileo observed that Venus showed phases

27 Galileo Galilei ( ) Phases of Venus Galileo observed that Venus showed phases enqrely like those of the moon from full to crescent, which it must do if the Copernican theory was correct. According to the Ptolemaic theory Venus would have to be a perpetual crescent. ObservaQons consistent with Copernicus, inconsistent with Ptolemy. 27

Galileo Galilei (1564 1642) Jupiter Has Moons Galilean Moons 4 Largest moons of Jupiter Io, Europa, Callisto, & Ganymede Galileo Galilei (1564 1642) 1632: "Dialogo Dei Massimi Sistemi Dialogue on the

28 Galileo Galilei ( ) Jupiter Has Moons Galilean Moons 4 Largest moons of Jupiter Io, Europa, Callisto, & Ganymede Galileo Galilei ( ) 1632: "Dialogo Dei Massimi Sistemi Dialogue on the Two Chief World Systems In Italian, Not Latin -- For the common people Two people, one representing the view of Ptolemy and other the view of Copernicus, present their arguments before an intelligent layman. The Pope Urban II thought that Simplico, the character who upheld the views of Ptolemy in the book, was a deliberate and insulqng caricature of himself 1633: Trial by Church (threatened with instruments of torture), forced to recant views "Eppur Si Muove "(And, yet it moves!") 28

29 1633: Galileo is ordered to his house in Arcetri, under house arrest, where he remains for the rest of his life. The book remained on the index of forbidden books unql 1822 Pope John Paul II finally gave an address that admiyed that there had been errors in the treatment of Galileo by the church, in ASIDE: Contrast Galileo with Nicolas Steno ( ), who laid the groundwork for the interpretaqon of the fossil record. See The Seashell on the Mountaintop by Alan Cutler. Modern ScienQfic Method 1. ObservaQons and Experiments Data which describes the physical world 2. Theory, Hypotheses, Models: - > Organize Facts from experiment & observaqons Unifying principles Make testable predicqons 29

CreaQonism and Intelligent Design vs. EvoluQon. The example of gravity as a scienqfic theory: Newton s Law c. 1700 AD Einstein s theory of General RelaQvity c.

30 CreaQonism and Intelligent Design vs. EvoluQon. The example of gravity as a scienqfic theory: Newton s Law c AD Einstein s theory of General RelaQvity c Photon versus wave descripqon of light The most interespng scienpfic quespons to work on for a professional scienpst are those we don't know the answer to. InteresPng theories to work on are those which fail to explain an observapon or fact. Many modern astronomers are deeply religious people. 30

The Astronomical Basis for Calendars The Earth rotates on its axis once a day. The Earth orbits the Sun with a period of about 365.

31 The Astronomical Basis for Calendars The Earth rotates on its axis once a day. The Earth orbits the Sun with a period of about days The Moon orbits the Earth, such that the period between new moon and new moon is days These periods vary a li7le bit because of the gravita9onal forces exerted by the other planets and other factors. Every 4 years, we take into account the days by added a leap day, February 29. Otherwise we would keep slipping, and eventually January would be summer in the northern hemisphere, etc. Now, the thing is that there are NOT an integral number of months ( days) in one year. So if for example today is a new moon, next year it will not be. The Gregorian Calendar (ChrisPan, one we use) is based on the mopon of the Earth around the Sun. The length and number of months have no connecpon to the mopon of the Moon It is based on the Julian Calendar, which was introduced by Julius Caesar in 45 BC. He made Jan. 1 the start of the Year. During the middle ages, different groups in Europe adopted different start dates for the new years. In 1582, Pope Gregory reformed the calendar, which is basically what we use today. The French recognized a different pope for a while and had a different calendar. 31

The Islamic Calendar is based on the mopon of the Moon, with no connecpon to the mopon of the Earth around the Sun. Hijri Calendar, Based on the Qur'an. Used in many countries around the Gulf, e.g.

Thus, a parpcular Islamic month falls during different Pmes of the year, e.g. Ramadan. Years are counted since the Hijra, which is is the Pme that Mohammed emigrated to Medina in AD 622.

The Jewish and Chinese Calendars combine both, so years are linked to the period of the orbit of the Earth around the Sun, AND months are linked to the mopon of the Moon around the Earth. 19 x365.

32 The Islamic Calendar is based on the mopon of the Moon, with no connecpon to the mopon of the Earth around the Sun. Hijri Calendar, Based on the Qur'an. Used in many countries around the Gulf, e.g. Saudi Arabia. Purely lunar: 12 months, each with days. Therefore the Islamic year has 12x29.53 = days The Islamic year is shorter than the Pme it takes the Earth to go around the Sun. Thus, a parpcular Islamic month falls during different Pmes of the year, e.g. Ramadan. Years are counted since the Hijra, which is is the Pme that Mohammed emigrated to Medina in AD 622. So AD 2009 is Islamic year The Jewish and Chinese Calendars combine both, so years are linked to the period of the orbit of the Earth around the Sun, AND months are linked to the mopon of the Moon around the Earth. 19 x = an integral number of day months. Jewish Year: A "ordinary" year has 355 days, and 12 months. A "leap" year has 385 days and 13 months. The length of a parpcular month varies from year to year by a day, so that if New Year's Day (Rosh HaShannah) is, say, a new moon, then the first day of every month is a new moon. Years are counted since the creapon of the world, taken to be 3761 BC. Thus 1998 is Jewish year

Astro 201: Sept. 2, 2010

Astro 201: Sept. 2, 2010 Do on- line prac:ce quiz #2 (see d2l) Homework #2: posted on web page aher class Today: Ancient Greeks Ptolemy V. Copernicus; retrograde mo:on Galileo Astronomical basis for calendars