the origin of modern astronomy chapter 4:. ancient greek astronomy models were generally wrong...
TRANSCRIPT
![Page 1: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/1.jpg)
The Origin of Modern Astronomy
Chapter 4:
![Page 2: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/2.jpg)
Ancient Greek Astronomy
• Models were generally wrong because they were based on wrong “first principles”, believed to be “obvious” and not questioned:
1. Geocentric Universe: Earth at the Center of the Universe.
2. “Perfect Heavens”: Motions of all celestial bodies described by motions involving objects of “perfect” shape, i.e., spheres or circles.
![Page 3: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/3.jpg)
Ancient Greek Astronomers
Aristotle
(384 – 322 B.C.), major authority of philosophy until the late middle ages: Universe can
be divided in 2 parts:
1. Imperfect, changeable Earth,
2. Perfect Heavens (described by spheres)
![Page 4: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/4.jpg)
Issues of Ancient Astronomy (I)
Fundamental argument for the geocentric universe:
Motion of Earth should result in an observable parallax, which was not seen.
![Page 5: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/5.jpg)
Issues of Ancient Astronomy (II)The retrograde (westward) motion of the planets
The “solution”: Epicycles!
![Page 6: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/6.jpg)
Introduced by Ptolemy (ca. A.D. 140)
The Ptolemaic system was considered the “standard model” of the universe until the Copernican Revolution.
![Page 7: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/7.jpg)
The Copernican Revolution
Nicolaus Copernicus (1473 – 1543):
heliocentric universe (sun in the center)
![Page 8: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/8.jpg)
Copernicus’ new (and correct) explanation for retrograde motion of the planets:
This made Ptolemy’s epicycles unnecessary.
Retrograde (westward) motion of a
planet occurs when Earth passes the
planet.
![Page 9: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/9.jpg)
Tycho Brahe (1546 – 1601)
Use of high-precision instruments for precise astronomical observations, meticulously reported in tables.
Later used by Kepler to develop laws of planetary motion.
![Page 10: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/10.jpg)
A Quadrant designed by Brahe
Used to precisely
measure an object’s angular distance above
the horizon
![Page 11: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/11.jpg)
Johannes Kepler (1571 – 1630)Used the precise
observational tables of Tycho Brahe to study
planetary motion mathematically.
1.Circular motion and
• Planets move around the sun on elliptical paths, with non-uniform velocities.
Found a consistent description by
abandoning both:
2.Uniform motion.
![Page 12: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/12.jpg)
Kepler’s Laws of Planetary Motion
1.The orbits of the planets are ellipses with the sun at one focus.
c
Eccentricity e = c/a
![Page 13: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/13.jpg)
Eccentricities of Ellipses
e = 0.02 e = 0.1 e = 0.2
e = 0.4 e = 0.6
1) 2) 3)
4) 5)
![Page 14: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/14.jpg)
Eccentricities of planetary orbitsOrbits of planets are virtually indistinguishable from circles:
Earth: e = 0.0167Most extreme example:
Pluto: e = 0.248
But their centers may be
significantly offset from the sun.
![Page 15: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/15.jpg)
3.A planet’s orbital period (P) squared is proportional to its average distance from the sun (a) cubed:
Py2 = aAU
3
2.A line from a planet to the sun sweeps over equal areas in equal intervals of time.
(Py = period in years; aAU = distance in AU)
![Page 16: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/16.jpg)
Galileo Galilei (1594 – 1642)
Introduced the modern view of science: Transition from a faith-based “science” to an
observation-based science.
Greatly improved on the newly invented telescope technology. (But Galileo did NOT invent the
telescope!)
Was the first to meticulously report telescope observations of
the sky to support the Copernican model of the universe.
![Page 17: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/17.jpg)
Major discoveries of Galileo (I):
• Moons of Jupiter
(4 Galilean moons)
• Rings of Saturn
(What he really saw)
![Page 18: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/18.jpg)
Major discoveries of Galileo (II):
• sunspots (proving that the sun is not perfect!)
![Page 19: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/19.jpg)
• Phases of Venus (including “full Venus”), proving that Venus orbits the sun, not Earth!
Major discoveries of Galileo (III):
![Page 20: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/20.jpg)
Historical Overview
![Page 21: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/21.jpg)
Isaac Newton (1643 - 1727)
• Building on the results of Galileo and Kepler
Major achievements:1. Invented calculus as a necessary tool to solve
mathematical problems related to motion
• Adding physics interpretations to the mathematical descriptions of astronomy by Copernicus, Galileo and Kepler
2. Discovered the three laws of motion
3. Discovered the universal law of mutual gravitation
![Page 22: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/22.jpg)
The Universal Law of Gravity
• Any two bodies are attracting each other through gravitation, with a force proportional to the product of their masses and inversely proportional to the square of their distance:
F = - G Mm
r2
(G is the gravitational constant.)
![Page 23: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/23.jpg)
Understanding Orbital MotionThe universal law of gravity allows us to
understand orbital motion of planets and moons:
• Earth and moon attract each other through gravitation.
Example:
Earth
Moon
v v’
v
F
• Since Earth is much more massive than the moon , the moon’s effect on Earth is small.• Earth’s gravitational force constantly accelerates the moon towards Earth.
• This acceleration is constantly changing the moon’s direction of motion, holding it on its almost circular orbit.
![Page 24: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/24.jpg)
Orbital Motion (II)In order to stay on a closed
orbit, an object has to be within a certain range of velocities:
Too slow : Object falls back down to Earth
Too fast : Object escapes the Earth’s gravity
![Page 25: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/25.jpg)
Orbital Motion (III):
Geosynchronous Orbits
![Page 26: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/26.jpg)
The TidesCaused by the
difference of the moon’s gravitational
attraction on the water on Earth
2 tidal maxima
Excess gravity pulls water towards the
moon on the near side
Forces are balanced at the center of Earth
12-hour cycle
Excess centrifugal force pushes water
away from the moon on the far side
![Page 27: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/27.jpg)
Spring and Neap Tides
The sun is also producing tidal effects, about half as strong as
the moon.
• Near full and new moon, those two
effects add up to cause spring tides
• Near first and third quarter, the two effects work at a right angle, causing neap tides.
Spring tides
Neap tides
![Page 28: The Origin of Modern Astronomy Chapter 4:. Ancient Greek Astronomy Models were generally wrong because they were based on wrong “first principles”, believed](https://reader036.vdocument.in/reader036/viewer/2022062802/56649eba5503460f94bc1ab7/html5/thumbnails/28.jpg)
Acceleration of the Moon’s Orbital Motion
Earth’s tidal bulges are
slightly tilted in the direction of Earth’s rotation
Gravitational force pulls the moon slightly forward along
its orbit