ASTA01 at UTSC

1
ASTA01 at UTSC Lecture 7

• Chapter 3The Origin of Modern Astronomy
• -Ancient astronomy
• The Copernican revolution
• De Brahe and Kepler
• Galileo
• Newton
• Later developments

2

• Have you ever looked up at the sky and marvelled
  at the multitude of tiny specks of light shining
  down on you?
• Have you tried to pick out patterns in the night
  sky?
• Have you stared at the full moon or the sliver of
  a crescent moon on a dark night?

3

• Then you are following in the footsteps of our
  ancient ancestors who gazed up at the sky
  thousands of years ago and took the first steps
  along the long road that has led to our current
  knowledge of the universe.
• As you read on, you will learn how the science of
  astronomy grew out of careful observations and
  gradual development of the scientific method over
  thousands of years.

4

• Every culture on Earth has engaged in and
  contributed to the development of astronomy,
  making it a truly global effort.
• Ancient astronomy has shaped not only our
  scientific thinking but also our culture, art,
  language, religions, and traditions.

5
A Brief History of Ancient Astronomy

• The origins of astronomy lay in the curiosity of
  our ancestors, who were excellent at observing
  and recording the world around them and
  recognizing patterns in what they observed.
• These skills were critical for survival in a
  hostile environment, but although they did not
  know it, careful observation and pattern
  recognition were also the first steps in what we
  now call the modern scientific method.

6
A Brief History of Ancient Astronomy

• A marvelous example of ancient observations and
  recordkeeping can be found in Lascaux, France,
  where Paleolithic cave paintings dating back to
  15 000 BCE were discovered in 1940.
• More than 900 images of animals show incredible
  attention to detail and anatomical precision.
• There are also numerous images of geometric
  figures.

7
A Brief History of Ancient Astronomy

• Cave in Lascaux, France, with a picture of
  Pleiades(?)

8
A Brief History of Ancient Astronomy

• Some recent scientific studies indicate that the
  paintings may have been a star map or
  astronomical calendar, but there is no conclusive
  proof that this theory is correct.

9
A Brief History of Ancient Astronomy

• More convincing evidence of early astronomical
  observations was found in Africa, where a carved
  bone that is 8500 years old shows pictographs of
  the crescent Moon.

10
A Brief History of Ancient Astronomy

• Ancient people of central Africa could predict
  seasons from the orientation of the horns of the
  crescent Moon each month (once again a result of
  careful observation and pattern recognition).
• This allowed them to determine when to plant
  seeds and grow their crops.

11
A Brief History of Ancient Astronomy

• Other ancient cultures also used astronomical
  observations for timekeeping.
• The motions of both the Sun and the Moon played
  an important role in the marking of time, with
  the Sun used for predicting seasonal changes and
  the lunar phases defining monthly changes.

12
A Brief History of Ancient Astronomy

• Some of the most careful observers and detailed
  record-keepers were the Babylonians.
• Babylon is now a city in Iraq, in Mesopotamia
  (region between the two rivers Tigris and
  Euphrates)
• The first female astronomer recorded in history
  was named in a Babylonian tablet from 2354 BCE.
  En HeduAnna was priestess of the Moon Goddess.

13
A Brief History of Ancient Astronomy

• Babylonian priests like En HeduAnna in
  Mesopotamia recorded the detailed motions of the
  visible planets on thousands of tablets more than
  4000 years ago.
• In 763 BCE, a solar eclipse was also observed and
  recorded by the Babylonians.
• Our division of circle into 3606060 units, and
  60 in one degree, as well as 60 in 1, derives
  from the sexagesimal counting system (base 60).

14
A Brief History of Ancient Astronomy

• These ancient astronomers have left their mark on
  modern astronomy.
• Our constellations of the zodiac are based on
  patterns identified by the Babylonians. Some
  names are Summerian
• (pre-Babylonian)

15
3 stars rising position on a Babylonian disk.
The Chaldean (Babylonian) priests-astrologers kne
w the 18-year Saros, the sun-moon cycle.
16
Venus tablets of Ammisaduqa (Babylon)
Tablet 63 of Enuma Anu Enlili (at the times of
gods Anu Enlil) - The 1st significant
astronomical text in history, dating to 1582-1562
BC, life of the 1st dynasty king
Ammi-Saduqa Records rising and setting times of
Venus over the period of 21 years.
17
A Brief History of Ancient Astronomy

• Around 4000 BCE, the Egyptians used their
  observations of the periodic rising of the star
  know to us as Sirius to mark the first day of a
  365-day calendar.

18
Egyptian astronomy Sirius Isis, Sun Ra

• "Her majesty Isis shines into the temple on New
  Years Day, and she mingles her light with that of
  her father Ra on the Horizon."

Denderah temple
19
A Brief History of Ancient Astronomy

• Sirius, the brightest star in the sky, which they
  identified with the fertility goddess Isis, first
  appeared in the predawn sky each year just as the
  Nile began its life-giving floods, on the 35th
  day of the year.
• (It disappeared on the western sky after sunset
  35 days prior to New Year)
• While the rising of the Nile varied year to year,
  Sirius appeared with perfect regularity.
• Once again, this helped them predict planting
  season and prepare for the floods, or inundations.

20
A Brief History of Ancient Astronomy

• The Egyptians were also the first to divide the
  night and day into 12 hours, using the rising of
  bright stars (later called decans) during summer
  nights.
• Our modern 24-hour clock owes its origins to the
  ancient Egyptians.

21
A Brief History of Ancient Astronomy

• Pyramids were aligned towards the pole star,
  which, because of the precession of the
  equinoxes, was at that time Thuban, a faint star
  in the constellation of Draco
• Temple of Amun-Re at Karnak, taking into account
  the change over time of the obliquity of the
  ecliptic, was aligned on the rising of the
  midwinter sun
• Pyramids were sort-of launchers of souls of dead
  pharaohs into the afterworld through the tunnel
  at the celestial pole corridors/shafts where
  oriented toward Thuban (serpent in Arabic).

22
A Brief History of Ancient Astronomy

• A 4000-year-old stone circle in Scotland marks
  the rise and set of the Moon during a phenomenon
  called the lunar standstill, which occurs every
  18.6 years due to the precession of the Moons
  orbital plane.
• During this time, the most northerly and most
  southerly rising and setting of the Moon occur
  every month.

23
A Brief History of Ancient Astronomy

• It is amazing that the builders of the stone
  circles in Scotland, as well as astronomers in
  other ancient civilizations, appeared to have
  been aware of this long-term cycle, which
  required careful observations over many years.

24
A Brief History of Ancient Astronomy

• Stonehenge, Scotland, ca. 2400 BCE

25
A Brief History of Ancient Astronomy

• At the famous monument at Stonehenge, England,
  completed around 1550 BCE, giant boulders are
  aligned to mark the rising and setting points of
  the Sun at the solstices.
• The site may have served as an observatory as
  well as a sacred ceremonial ground.

26
A Brief History of Ancient Astronomy

• The Mayans also built massive ancient structures,
  such as the Templo Mayor, to mark seasonal events.

27
A Brief History of Ancient Astronomy
28
A Brief History of Ancient Astronomy

• In 1400 BCE, an exciting event was observed and
  recorded in China the sudden brightening and
  dimming of a guest star.
• Although they did not know it at the time, the
  Chinese had made the earliest known record of a
  supernova explosion.
• The Chinese also recorded solar and lunar
  eclipses continuously from the fifth century BCE!

29
A Brief History of Ancient Astronomy

• In 1054 CE another powerful supernova explosion
  was recorded by the Chinese.
• This spectacular event also may have been
  depicted in a famous Anasazi rock painting on the
  other side of the world, in New Mexico, USA.
• The supernova explosion was powerful enough to be
  brighter than Venus and visible during the day
  for 23 days!

30
A Brief History of Ancient Astronomy

• Today, modern telescopes have been used to
  capture stunning images of the Crab nebula, which
  is the remnant of the supernova explosion of 1054
  CE.

31
A Brief History of Ancient Astronomy

• The observed connection between the planting
  seasons and the position of celestial objects led
  to the development of religions centred on the
  Sun, the Moon, and other celestial objects that
  were personified as deities.

32
A Brief History of Ancient Astronomy

• Various ceremonies were designed to please
  celestial beings, and prayers and rituals to mark
  important seasonal changes were performed.
• Many festivals and ceremonies still celebrated in
  various parts of the world today have their roots
  in these ancient practices.

33
A Brief History of Ancient Astronomy

• Priests became important members of society
  thanks to their ability to predict celestial
  events, which was viewed as a connection to
  heavenly deities.
• The association of celestial objects with one or
  more gods led to the idea that these gods could
  affect individual human lives.

34
A Brief History of Ancient Astronomy

• This was the birth of astrology the search for
  influences on human lives based on the positions
  of planets and stars in the sky.
• However, numerous scientific tests have shown
  that astrological predictions are no more
  accurate than we should expect from pure chance.

35
ASTROLOGY

• If you were take only one thing from this
  lecture, it would be that we are dealing in
  ASTA01 with astronomy not astrology.
• Astrology is guessing the best time to do
  important things (electoral astrology), or a
  persons character or future (natal astrology), or
  finding an answer to a question (mundane a.) from
  the positions and patterns of planets in the sky.
  It is non-scientific and unproven, but popular,
  partly because horoscopes and predictions sell
  well. In the past, it was used in place of
  todays medicine and meteorology as well.

36
A Brief History of Ancient Astronomy

• The days of the week were named for the Sun, the
  Moon, and the five planets visible to the naked
  eye.
• Mones dag -gt Monday
• Tyrs dag ? Tuesday
• Odins dag ? Wedneday
• Thors dag ? Thursday
• Freya dag ? Friday
• Saturns day ? Saturday
• Suns day ? Sunday

37
A Brief History of Ancient Astronomy

• Astronomical observations benefited and impacted
  ancient societies in many ways, including
  timekeeping, efficient agricultural practices,
  navigation, and the development of religious and
  ceremonial practices.

38
A Brief History of Ancient Astronomy

• Thus far astronomy had only involved making
  observations, recognizing basic patterns, and
  making rudimentary predictions.
• A crucial part of the scientific method
  building and testing models and hypotheses was
  missing.
• This was about to change in Greece.

39
The Geocentric Model of the Universe

• The ancient Greeks were interested in building
  models of nature based on reasoning and
  observation.
• Thales of Miletus, an influential scientist and
  mathematician, assumed that the world was
  understandable and attempted to create models to
  explain major events in the universe.
• It was said that he correctly predicted a solar
  eclipse in 585 BCE.

40
Early materialist philosophers Leucippus and
Democritus
Some of the earliest recorded physics was very
far-sighted essentially correct!
Democritus predicted evolution
(formation/decay), role of disks, and
diversity of worldsplanets.
41
Antique theory 1 plurality of worlds Kosmos
unique or multiple (infinite in number?) Greek
atomists Leucippus and Democritus considered the
world built of the same (solar abundance')
atomic matter that forms the Earth, subject to
constant motion through vacuum, collision, and
coalescence (accretion). Ancient atomists wrote
about what we now call the solar nebula The
worlds come into being as follows many bodies of
all sorts and shapes move from the infinite into
a great void they come together there and
produce a single whirl, in which, colliding with
one another and revolving in all manner of ways,
they begin to separate like to like. Leucippus
(480-420(?) B.C.), after Diogenes Laertios (3rd
c. A.D.)
42
This following predictions make anticipate
planets around pulsars and binary stars
evolutionary aspect stressed hot planets. In
some worlds there is no Sun and Moon, in others
they are larger than in our world, and in others
more numerous. In some parts there are more
worlds, in others fewer (...) in some parts they
are arising, in others failing. There are some
worlds devoid of living creatures or plants or
any moisture. Democritus (ca. 460-370 B.C.),
after Hyppolytus (3rd cent. A.D.) Plurality and
diversity of planetary systems reaffirmed There
are infinite worlds both like and unlike this
world of ours. For the atoms being infinite in
number, as was already proven, (...) there
nowhere exists an obstacle to the infinite number
od worlds. Epicurus (341-270 B.C.) Similar
writings by Lucretius (ca. 99-55 B.C.).
43
Antique theory 2 a unique terrestrial
system The atomist system was eclipsed by a
cohesive system of Aristotle, (384-322 B.C.), a
student of Plato and tutor of Alexander the
Great. Aristotle was not very interested in
extrasolar planetary systems or their formation,
or other unobservable things. But (unfortunately)
he was extremely influential after 1.5103 yrs.
His world was geocentric, unchanging and unique.
The four elements moved each to their 'natural
place' with respect to the center of the world.
The existence of many such centers was
unthinkable There cannot be more worlds than
one. Aristotle
44
The Geocentric Model of the Universe

• In 500 BCE, Pythagoras suggested that the Earth
  was a sphere and not flat, as had been previously
  assumed.
• His model was primarily based on the widely held
  belief that the sphere is an object of
  geometrical perfection.

45
The Geocentric Model of the Universe

• Based on this spherical model, Eratosthenes was
  able to calculate the Earths circumference by
  observing the position of the Sun at noon in two
  different cities on the first day of summer.
• Incredibly, his estimate was accurate to within a
  few percent of the currently known value.

46
The Geocentric Model of the Universe

• The two great authorities of Greek astronomy were
  the brilliant philosopher Aristotle and a later
  follower of Aristotles principles, Claudius
  Ptolemy (pronounced TAHL-eh-mee the P is
  silent).

47
The Geocentric Model of the Universe

• Ancient Greek philosophers and astronomers
  accepted without question that heavenly objects
  must move on circular paths at constant speeds,
  and that Earth is motionless at the centre of the
  universe.
• This geocentric (Earth at the centre) model was
  championed by Aristotle.
• Although a few ancient writers mentioned the
  possibility that Earth might move, most of them
  did so in order to point out how that idea is
  obviously wrong.

48
The Geocentric Model of the Universe

• As viewed by you from Earth, the planets seem to
  follow complicated paths in the sky, including
  episodes of backward motion that are difficult
  to explain in terms of motion on circular paths
  at constant speeds.

49
The Geocentric Model of the Universe

• You can see how Ptolemy created an elaborate
  geometrical and mathematical model to explain
  details of the observed motions of the planets
  while assuming Earth is motionless at the centre
  of the universe.

50
The Geocentric Model of the Universe

• Aristotle lived in Greece from 384 to 322 BCE.
• He believed as a first principle that the heavens
  were perfect.
• Because the sphere and circle were considered the
  only perfect geometrical figures, Aristotle also
  believed that all motion in the perfect heavens
  must be caused by the rotation of spheres
  carrying objects around in uniform circular
  motion.

51
The Geocentric Model of the Universe

• Aristotles writings became so famous that he was
  known throughout the Middle Ages as The
  Philosopher, and the geocentric universe of
  nested spheres that he devised dominated
  astronomy.

52
The Geocentric Model of the Universe

• Claudius Ptolemy, a mathematician who lived
  roughly 500 years after Aristotle, believed in
  the basic ideas of Aristotles universe but was
  interested in practical rather than philosophical
  questions.
• For Ptolemy, first principles took second place
  to accuracy.
• He set about making an accurate mathematical
  description of the motions of the planets.

53
The Geocentric Model of the Universe

• Ptolemy weakened the first principles of
  Aristotle by moving Earth a little off-centre in
  the model and inventing a way to slightly vary
  the planets speeds.
• This made his model (published around 140 CE) a
  better match to the observed motions.

54
The Geocentric Model of the Universe

• Ptolemys model could thus handle the complicated
  retrograde motion of the planets.
• Aristotles universe, as embodied in the
  mathematics of Ptolemys model, dominated ancient
  astronomy for almost 1500 years.

55
The Geocentric Model of the Universe

• One of Aristotles students was the military
  leader Alexander the Great.
• Although he used military force to conquer much
  of the Middle East all the way to India, he also
  promoted science and encouraged learning.

56
The Geocentric Model of the Universe

• He founded the city of Alexandria in Egypt, on
  the delta of Nile river, renowned for its great
  library that eventually gathered 500,000 papyrus
  scrolls (books) and served as a major centre of
  knowledge for hundreds of years.
• One of the most famous library scholars was a
  female astronomer and mathematician named
  Hypatia, whom we would today call the director of
  the observatory in Alexandria.

57
The Geocentric Model of the Universe

• Hypatia was a well-respected scientist and
  teacher, and wrote several books on algebra,
  geometry, and astronomy.
• She may have also edited past work by Ptolemy.
• She was eventually killed by religious fanatics
  in 415 during a highly turbulent time of
  political struggle between the secular Roman
  governor Orestes and Christian bishop Cyril.
  Shortly afterwards the library of Alexandria was
  destroyed.

58
The Geocentric Model of the Universe

• Despite the librarys destruction, Greek
  knowledge was not lost, but was preserved in the
  Islamic world.
• Caliph Al-Mamuns House of Wisdom in Baghdad was
  a great centre of learning around 800 CE.

59
The Geocentric Model of the Universe

• Many ancient texts by scientists and
  mathematicians from India were also translated
  into Arabic during this time.
• Foremost among these was Aryabhatiya, by the
  Indian astronomer and mathematician Aryabhata.
• In it, a planetary model was described that was
  geocentric but included the possibility of the
  Earth spinning on its own axis.

60
The Geocentric Model of the Universe

• Building on ancient texts from Greece, India,
  China, and Babylon, Arab scientists made many
  advances in mathematics and astronomy.
• The Greek geocentric models were expanded and
  corrected, and many new astronomical observations
  were made.
• The names of numerous stars today, such as Algol
  or Deneb, have their roots in this golden age of
  astronomy.

61
The Geocentric Model of the Universe

• Although the Ptolemaic geocentric model was
  widely accepted, some philosophers such as Abu
  Rayhan al-Biruni started thinking about
  arguments for a heliocentric model.
• It is likely that Arab astronomers were aware of
  the heliocentric model proposed by the Greek
  philosopher Aristarchus in 270 BCE.

62
The Geocentric Model of the Universe

• Meanwhile, in India, Nilakantha Somayaji
  developed a partially heliocentric model that
  included elliptical orbits and the Earths
  rotation.
• After the fall of Constantinople (now Istanbul)
  in 1453, many scholars travelled to Europe,
  carrying with them knowledge that contributed to
  the birth of the Renaissance.
• The stage was set for a revolution in scientific
  thought.

63
Medieval theories The pendulum starts swinging
Aristotle's work rediscovered in 13th century,
starts Renaissance in Europe. For 100 years
everybody agrees with him on most issues.
Roger Bacon (1214-1292) at Oxford cites the
argument about the impossibility of vacuum
between the planetary systems. A similar
thinking prevailed at other rising universities,
like Paris. But the Aristotelian insistence on
unity and uniqueness begun to contradict the
Christian doctrine of the time.
64
In 1277 Etienne Tempier, the bishop of Paris,
condemned opinions based on 219 statements in
Aristotelian writings, among them "that the
First Cause cannot make many worlds". The
many-worlds opinion was hotly contested at the
universities but prevailed, as was mandated by
the Church under the threat of excommunication.
The Church mandates(!) the many-worlds view in
13th century