* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download A Sun-Centered Universe - Sierra College Astronomy Home Page
Non-standard cosmology wikipedia , lookup
Patronage in astronomy wikipedia , lookup
History of Solar System formation and evolution hypotheses wikipedia , lookup
Constellation wikipedia , lookup
Lunar theory wikipedia , lookup
Physical cosmology wikipedia , lookup
Shape of the universe wikipedia , lookup
Chinese astronomy wikipedia , lookup
Archaeoastronomy wikipedia , lookup
Rare Earth hypothesis wikipedia , lookup
Fine-tuned Universe wikipedia , lookup
Observable universe wikipedia , lookup
Chronology of the universe wikipedia , lookup
Extraterrestrial skies wikipedia , lookup
Flatness problem wikipedia , lookup
Comparative planetary science wikipedia , lookup
Astrobiology wikipedia , lookup
Extraterrestrial life wikipedia , lookup
Astronomical unit wikipedia , lookup
Copernican heliocentrism wikipedia , lookup
Astronomy in the medieval Islamic world wikipedia , lookup
Observational astronomy wikipedia , lookup
International Year of Astronomy wikipedia , lookup
Dialogue Concerning the Two Chief World Systems wikipedia , lookup
Theoretical astronomy wikipedia , lookup
Geocentric model wikipedia , lookup
History of astronomy wikipedia , lookup
Hebrew astronomy wikipedia , lookup
Pick up 3rd hour stuff! 3rd hour stuff will first appear in the center of the room before lecture. It will then be moved to the box labeled “3400” outside the planetarium All 3rd hours will collect there until the end of the semester Scores posted just outside the planetarium (listed by 4-digit ID number) Answers posted online Third Hour This week: Star Charts! Bring Star Charts! Lecture 3a: An Earth-Centered Universe Terms Observer coordinates: altitude, azimuth, zenith, horizon, meridian Earth coordinates: latitude, longitude, north pole, equator Celestial coordinates: declination, right ascension, north celestial pole, celestial equator Angles: degree, minute of arc, second of arc, angular separation Earth in CS Lecture 3a: An Earth-Centered Universe Ancient Astronomy There are many ancient artifacts of astronomy Aztec Templo Mayor Chaco Canyon of the Anasazi Aztec Chaco – Includes sun dagger Machu Picchu in Peru Stonehenge in England © Sierra College Astronomy Department Sun dagger Machu Stonehenge 3 Lecture 3a: An Earth-Centered Universe Mesopotamian/Babylonian Astronomy Made the first long term records of astronomy Created the 12 zodiacal constellations Developed the angle measuring system we use Used leap months in calendar Discovered patterns of planetary motions by keeping track of synodic periods Interest in planetary positions was due to their interest in astrology, the belief that the positions of celestial objects influence events on the Earth They developed mathematical description of planetary motions and could make crude predictions © Sierra College Astronomy Department 4 Lecture 3a: An Earth-Centered Universe Pythagoras (c.582-c.500 BC) and his Students It was Pythagoras (or his students) who rejected the notion of a flat Earth and embraced the idea of a spherical Earth His model of the universe had Earth revolving around a “central fire” which could not be seen because it was blocked by a “counter Earth”. The moon and Sun around traveled around the central fire. Pythag © Sierra College Astronomy Department 5 Lecture 3a: An Earth-Centered Universe Eudoxus (408-355 BC) He proposed that planetary motions were a combination of circular motions He put the earth in center and planets were attached to spheres which moved at the appropriate rates to roughly reproduce their motions. Exodus © Sierra College Astronomy Department 6 Lecture 3a: An Earth-Centered Universe Aristotle (384-322 BC) Physical theory of dynamics We have a comprehensive theory, a framework for questions. Applications: motions: up, down, around essences: earth, water, air, fire, ether simple vs. compound circular motion: complete, unchanging Comets: clearly changeable, must be meteorological Planets: compound circular motion Spherical Earth Also made cogent arguments about the spherical shape of Earth © Sierra College Astronomy Department 7Spherical Earth2 Lecture 3a: An Earth-Centered Universe Aristarchus (310-230 BC) Dimensions of the Moon Angular size (0.5 degrees) Linear size (inferred from lunar eclipses) Distance (Small Angle Formula relates distance to angular and linear size) An example of a geometric approach to astronomy Made first estimate of Earth-Sun distance (relative to Earth-Moon distance) Also suggested a Sun-centered universe © Sierra College Astronomy Department eclipse F8 Geometry Small angle Formula (Don’t use) 8 D q d So, what is the angular size of the Moon? © Sierra College Astronomy Department 9 Lecture 3a: An Earth-Centered Universe Eratosthenes (276-195 B.C.) Measuring the Size of Earth Alexandria Eratosthenes devised a clever way to measure the Earth’s size. He observed that when the Sun was overhead (at the zenith) at Syene, it was 7° from overhead at Alexandria. Since 7° is about 1/50 of a full circle (360°), the circumference of the Earth should be 50 times the distance from Syene to Alexandria, or 50 x 5,000 stadia = 250,000 stadia. © Sierra College Astronomy Department Erato Erato2 10 Lecture 3a: An Earth-Centered Universe Eratosthenes 250,000 stadia roughly translates into 45,000 km, based on our best guess as to the size of a stadium. The Earth’s actual circumference is about 40,000 km, so Eratosthenes calculation is 12% too big. But his geometrical method is correct. Earth’s circumference of 40,000 km gives a diameter of about 13,000 km (~ 8,000 mi). © Sierra College Astronomy Department 11 Lecture 3a: An Earth-Centered Universe Hipparchus Hipparchus A discovery of a “new” star in 134 B.C. prompted him to make a catalogue of the brighter stars This led to another discovery: precession of the poles – Hipparchus noticed the vernal equinox drifted westward 1° every 78 years implying it would take 26,000 years to travel the full cycle of 360° along the ecliptic – This was due to the earth’s poles slow movement on the celestial sphere, completing a loop in about 26,000© years Sierra College Astronomy Department precess 12 Lecture 3a: An Earth-Centered Universe Claudius Ptolemy (127-151 AD) Claudius Ptolemy Worked in at the Great Library at Alexandria Invented the latitude and longitude system Wrote a book on astronomy – megisth – Often referred to as Almagest = “the Greatest” – Contained improved methods to find distance to the Sun and Moon – May have taken some ideas from Hipparchus © Sierra College Astronomy Department 13 Lecture 3a: An Earth-Centered Universe Claudius Ptolemy (127-151 AD) Claudius Ptolemy is credited for devising the first predictive model of the universe, the Ptolemaic model (A.D. 150) Discredited Aristarchus’s Sun-centered model with incorrect assumptions Philosophical keys: use circles, have uniform circular motion The Sun, Moon and each planet moved upon an epicycle, the center of which revolved around a deferent circle Compound circular motion allowed planets to have retrograde motion © Sierra College Astronomy Department 01-20C Retrograde Ptolemaic Model 01-22 Ptolemy, Mars 01-23C Ptolemy, Mercury and Venus 14 Lecture 3a: An Earth-Centered Universe Claudius Ptolemy 01-20C Retrograde To improve accuracy, Ptolemy had to offset the Earth from the center of the deferent Ptolemaic and make the uniform circular motion Model relative to another point, equally offset from center called the equant It is difficult to know whether Ptolemy believed the universe actually worked this way, or was this simply a model that gave fairly accurate predictions. D-7 01-22 Ptolemy, Mars 01-23C Ptolemy, Mercury and Venus © Sierra College Astronomy Department 15 Lecture 3a: An Earth-Centered Universe Criteria for Scientific Models (Slide from Lecture 1b in Handbook) Three modern criteria of scientific models: – Model must fit the data – Model must make predictions that can be tested and be of such a nature that it would be possible to disprove it – Model should be aesthetically pleasing simple, neat, and elegant (Occam’s razor) Lecture 3a: An Earth-Centered Universe Criteria for Scientific Models Ptolemy’s model meets the first two criterion for a good scientific model fairly well but it is much less successful with the third (aesthetically pleasing). Earth not quite in the center Scale of deferents and epicycles arbitrary Not quite uniform circular motion © Sierra College Astronomy Department 17 See Chapter S1, p 93 Lecture 3: Patterns in the Sky Observation: The Planets Inferior The early observers noted several planetary configurations Opposition: when a planet and Sun appear in the opposite part of the sky (Elongation = 180°) Superior – Only happens for Mars, Jupiter, Saturn Conjunction: when the planet and Sun appear together in the sky (Elongation = 0°) Greatest Elongation: when Mercury or Venus reaches a maximum elongation angle during a particular apparition The time it took a planet to return to a particular configuration (e.g. conjunction, opposition) was called the synodic period. Plan. © Sierra College Astronomy Department Config. (Space) Plan. 18 Config. Other Slides © Sierra College Astronomy Department 19 Lecture 3a: An Earth-Centered Universe Small Angle Formula angular diameter(q ) linear diameter(D ) distance(d ) 206, 265" Solved for d: distance(d ) linear diameter(D ) angular diameter(q ) 206, 265" For the moon: F8 Linear diameter = 3476 km Distance from Earth = 384,000 km Therefore the angular diameter is 1870” 0.5o See Text © Sierra College Astronomy Department Geometry Small angle formula 20 Lecture 3a: An Earth-Centered Universe Small Angle Formula angular diameter(q ) linear diameter(D ) distance(d ) 206, 265" Solved for d: distance(d ) linear diameter(D ) angular diameter(q ) For the moon: Angular diameter = 0.5o = 1800” Linear diameter = 3/8 Earth’s diameter 206, 265" F8 Geometry Small angle formula Therefore the distance to the moon is calculated to be 42 Earth diameters, though the actual answer must be smaller See Text 21 © Sierra College Astronomy Department