Unit 11:
Gravity & the Solar System
•Historical development
•Kepler’s Laws
•Newton’s Universal Gravitation
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Inquiry Physics
www.inquiryphysics.org
11: Gravity & the Solar System
Historical development
• Eudoxus & Aristotle
• Ptolemy
• Copernicus
• Pope Gregory XIII
• Galileo
• Brahe
• Kepler
• Newton
• Einstein
Next Index
11: Gravity & the Solar System
Historical development
Name Era Location Achievement
Eudoxus &
Aristotle 300 BCE -
100 BCE Greece
Geocentric model with concentric crystal spheres;
orbits are circular with
epicycles (circles on circles)
(click thumbnails to view large images & movies) Next
Index
11: Gravity & the Solar System
Historical development
Name Era Location Achievement
Ptolemy 100s Egypt
Developed most accurate
version of geocentric
model in his Almagest, with 1000-star catalog
(click thumbnails to view large images & movies) Next Index
11: Gravity & the Solar System
Historical development
Name Era Location Achievement
Copernicus Early
1500s Poland
Developed a heliocentric
model, but orbits still circular with epicycles
(click thumbnails to view large images & movies & applets) Next Index
11: Gravity & the Solar System
Historical development
Name Era Location Achievement
Pope
Gregory XIII Late 1500s Italy
Ordered calendar fix:
10 days omitted in 1582 and 3 Julian leap days are omitted every 400 years
(England and its colonies did not adopt this calendar until 1752)
Next Index
11: Gravity & the Solar System
Historical development
Name Era Location Achievement
Galileo Mid 1600s Italy
Supported Copernican model with telescopic
observations in The Starry Messenger; persecuted by religious authorities
(click thumbnails to view large images & applets) Next Index
11: Gravity & the Solar System
Historical development
Name Era Location Achievement
Brahe Late 1500s Denmark
Used parallax to show supernova & comet out among the spheres;
collected 20 years of
incredibly accurate naked- eye observations
(click thumbnails to view large images & applets) Next Index
11: Gravity & the Solar System
Historical development
Name Era Location Achievement
Kepler Early
1600s Germany
Analyzed Brahe's data to
discover 3 laws of planetary motion
(click thumbnails to view large images) Next Index
11: Gravity & the Solar System
Historical development
Name Era Location Achievement
Newton Late 1600s England
Explained all of Kepler’s Laws with a single
equation:
F
g= Gm
1m
2d
2(click thumbnails to view large images & applets) Next Index
11: Gravity & the Solar System
Historical development
Name Era Location Achievement
Einstein Early
1900s Switzerland,
Germany
Explained gravity as a warp in the spacetime
continuum in his General Theory of Relativity
(click thumbnails to view large images & movies) Next Index
11: Gravity & the Solar System
Kepler’s Laws
1. Planets move in ellipses with the sun off-center at one focus.
(click to enlarge)
Next Index
11: Gravity & the Solar System
Kepler’s Laws
1. Planets move in ellipses with the sun off-center at one focus.
2. Planets sweep out equal areas in equal time, so
they speed up when closer to the sun.
(click to enlarge)
(click for simulation)
Next Index
11: Gravity & the Solar System
Kepler’s Laws
1. Planets move in ellipses with the sun off-center at one focus.
2. Planets sweep out equal areas in equal time, so
they speed up when closer to the sun.
3. The square of a planet’s period is directly
proportional to the cube of its average orbital
radius.
(click to enlarge)
(click for simulation)
(click to enlarge)
Index
Next
11: Gravity & the Solar System
Newton’s Law of Universal Gravitation
• NASA J-Track 3D satellite tracking
• International Space Station
• Voyager Mission
• Exosolar Planets
Index
Next
Unit 11:
Gravity & the Solar System
All images, videos, simulations, and other resources used and linked to in this presentation are being utilized under the educational fair use doctrine of United States copyright law.
Index
Inquiry Physics
www.inquiryphysics.org
This presentation is Creative Commons licensed for free distribution for non-commercial use when attributed to
Granger Meador
Greek
Geocentric Model
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Epicycles create retrograde motion in a geocentric system
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Excerpt of Greek translation of Ptolemy’s Almagest on the orbit of Mercury
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The Ptolemaic Model
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Nicholas
Copernicus, who proposed a sun- centered system
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Excerpt from On the
Revolutions of the Heavenly Spheres
by Copernicus
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Retrograde motion is actually due to varying orbital speeds around the sun
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Galileo Galilei supported a sun-centered system
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Two of Galileo’s telescopes
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Moon sketches in Galileo’s The Starry Messenger
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Galileo at the inquisition (Relevant Scripture)
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Galileo at the inquisition (Relevant Scripture)
Psalm 93:1 - "The Lord reigns, he is robed in majesty; the Lord is robed in majesty and is armed with strength. The world is firmly
established; it cannot be moved."
Psalm 104:5 - (Speaking of God.) "He set the earth on its foundations; it can never be moved."
Ecclesiastes 1:5 - "The sun rises and the sun sets, and hurries back to where it rises."
Joshua 10:12-14 - (Joshua prays to have sun and moon stand still.) "The sun stopped in the middle of the sky and delayed going down about a full day."
Habakkuk 3:11 (Habakkuk prays.) "Sun and moon stood still in the heavens at the glint of your flying arrows, at the lightning of your
flashing spear."
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Tycho Brahe, who collected reams of data on stars and planets
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X-ray image of the supernova of 1572
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Brahe’s plot of the trajectory of the comet of 1577 across the crystal spheres
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Brahe’s Uraniborg Castle
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Brahe’s Quadrant at Uraniborg
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Brahe’s
Stjerneborg Observatory (Modern-Day)
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Brahe’s
Stjerneborg Observatory Today
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Johannes Kepler, who discovered 3 laws of
planetary motion
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Two of the thousands of pages from
Kepler’s years of calculations on the orbit of Mars
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Comparing the accuracy of the Copernican vs. Keplerian systems
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Isaac Newton, who linked the heavens and earth with his equation for gravity
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Woolsthorpe, where Newton supposedly saw the apple fall
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Albert Einstein, when he was a
teenager pondering what it would be like to ride a beam of light
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Simulation of a black hole passing in front of a distant galaxy, acting as a gravitational lens
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Galaxy cluster in center of image is a lens creating many distorted images of a
distant blue galaxy in a ring around it
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How the two foci are used to draw an ellipse
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y 3 α x 2 r 3 α T 2
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International Space Station, photo taken from a space shuttle in December 2006 ISS Tracking
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A Famous Use of Newton’s Law:
Two Voyager probes were launched in 1977, carrying cameras and other sensors to the outer gas giants.
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The two Voyager space probes show the utility of Newton’s equation. They were launched in 1977 and coasted by
planet after planet, steered by the gravity of each successive planet as calculated years previously.
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The Voyager probes gave us our first close-up views of Jupiter, Saturn, Uranus, and Neptune. These gas giants dwarf the Earth.
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On the left, the moon Io is above Jupiter’s Great Red Spot, which has swirled for over 300 years and is larger than Earth.
Over to the right is the moon Europa.
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Io is volcanic, spewing sulfur, and has mountains up to 52,000 feet high.
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Icy Europa, in contrast to Io, is the smoothest object in the solar system and probably has a buried liquid water ocean.
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Saturn’s rings are mostly ice and dust.
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Voyager revealed that one of Saturn’s outer rings is maintained by two “shepherd” moons, one on each side. Their gravity acts to sweep up particles to maintain the ring.
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Uranus looked almost featureless, but Voyager could detect cloud patterns. The planet is tipped over on its side with one pole always at high noon and the other in perpetual darkness.
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Miranda is a moon of Uranus. It is about half water ice and half rock, with very odd features that may be upwellings of ice.
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Neptune had an Earth-sized dark hurricane in progress during the flyby. The Hubble Space Telescope showed it had disappeared by 1994, but a similar storm then formed in the opposite hemisphere.
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Triton is Neptune’s largest moon and features ice volcanoes.
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The pale blue dot is Earth as seen by Voyager 1 in 1990 as it left the solar system.
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Positions of Voyager 1 and 2 in October 2006. Voyager 1 is now over 100 times farther from Sol than is Earth, headed out at over 38,000 mi/h. Even at that speed the spacecraft would take tens of thousands of years to reach another star.
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Newton’s Law allows
scientists to watch the shifting light from a star and deduce the approximate mass and location of large planets since their gravitational pull makes the star wobble.
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