Chapter 3: The Planet Puzzle

Galileo observed that venus had phases that correlated with its size in his telescope. From this information, you may conclude

orbits the sun

Aristarchus (310 BCE to 210 BCE)

proposed that the daily motions in the heavens, the rising and setting the of the Sun and Moon and the seeming rotation of the Celestial Sphere, were due to the Earth rotating on its axis. proposed that the Earth was circling the Sun explained that the stars are so far away that the shift is too small to see.

Galileo Observed that jupiter has moons. From this information you may conclude that

some things do not orbit the earth

Copernicus

1473-1543. Polish astronomer who was the first to formulate a scientifically based heliocentric cosmology that displaced the earth from the center of the universe. This theory is considered the epiphany that began the Scientific Revolution. took the idea from Aristarchus that the daily motions of the heavens were due to the rotation of the Earth on its own axis, and that he figured that the motion of the Sun along the Ecliptic and the seasons of the year are due to the Earth moving around the Sun.

Copernicus said that the daily motions in the heavens were caused by the

Earth turning on its axis.

Kepler's Second Law

Equal Area Rule A line drawn from a planet to the sun sweeps out equal areas in equal times.

Kepler's First Law

Law of Planetary Motion The orbit of each planet is an ellipse with the Sun at one focus.

Kepler's Third Law

The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit. T = time that planet takes to go once around the Sun R = planets average distance from the Sun (R is half of the longest diameter of the planets elliptical orbit) T2/R3 has the same value for every planet. Earth: T = 1 R = 1 T2/R3 = 1. when you compare the speeds at which different planets move, closer is faster

To account for motions in the heavens they assumed:

The stars are attached to a crystal sphere, which rotates around the Earth. The Sun and Moon rotate around the Earth separately from crystal sphere. Each planet moves around the Earth in a complicated path.

Johannes Kepler

Tycho's assistant near the end of Tycho's life advocate of the Copernican system

Copernicus said that the rotation of the Earth on its axis caused the a. daily motions in the heavens. b. phases of the Moon. c. retrograde motion of the planets. d. eclipses of the Moon. e. motion of the Sun along the ecliptic.

a. daily motions in the heavens.

As the two foci of an ellipse are moved apart, the shape of the ellipse becomes a. more like a line between the foci. b. more like a circle around the foci. c. more like a triangle drawn around the foci. d. more like a sphere around the foci.

a. more like a line between the foci.

Kepler's First Law of Planetary Motion is that the orbit of each planet is

an ellipse with the Sun at one focus.

Kepler found that the orbit of Mars is best described as

an ellipse.

The statement that the orbit of each planet is an ellipse with the Sun at one focus is due to a. Copernicus. b. Galileo. c. Kepler. d. Newton.

c. Kepler.

Mars is farther from the Sun than Earth. Which of the following statements is true? a. Mars takes longer to go around the Sun than the Earth because it has farther to go, but actually moves faster than the Earth. b. Mars takes longer to go around the Sun than the Earth because it has farther to go, but actually moves at the same speed as the Earth. c. Mars takes longer to go around the Sun than Earth and moves more slowly than the Earth does. d. Mars takes less time to go around the Sun than the Earth and moves much faster. e. Mars takes less time to go around the Sun than the Earth does but moves slower because the Earth keeps making rest stops.

c. Mars takes longer to go around the Sun than Earth and moves more slowly than the Earth does.

Which of Kepler's Laws governs how a particular planet speeds up and slows down? a. The Period-Radius Relation. b. Orbits are Ellipses. c. The Equal Area Law. d. The Law of Inertia. e. The Law of Averages.

c. The Equal Area Law.

In comparison to the Copernican Theory, the Ptolemaic Theory made predictions that were of a. much higher accuracy. b. much less accuracy. c. about the same accuracy.

c. about the same accuracy.

One reason that the Copernican System failed to fit Tycho's observations was that a. it placed the Earth at the center of the universe. b. it used elliptical orbits instead of circles. c. it used circular orbits instead of ellipses. d. it placed the Sun at the center of the system.

c. it used circular orbits instead of ellipses.

By making extensive observations of planetary motion, Tycho Brahe a. discovered new planets. b. explained how planets move. c. provided accurate data for the first time. d. disproved Ptolemy's theory of planetary motion. e. proved that Copernicus was right.

c. provided accurate data for the first time.

The ancient Greeks argued that the Earth cannot be moving because such a motion would cause apparent shifts in the positions of stars. This argument was wrong because a. no such shifts are actually possible. b. all of the stars are at the same distance from the Earth. c. the stars are so far away that the shifts due to the Earth's motion are extremely small. d. each star is moving in a circle exactly in step with the Earth's motion around the Sun.

c. the stars are so far away that the shifts due to the Earth's motion are extremely small.

The Ptolemaic model of the Solar System has each planet moving along a

circular epicycle whose center, in turn, moves around the Earth.

Tycho Brahe's careful observations of the planets agreed, to within observational error, with a. the Copernican System. b. the Ptolemaic System. c. the Tychonic System. d. None of these systems.

d. None of these systems.

Which of these was the Solar System model that assumed the Earth is fixed and the Sun, Moon, and planets all move on epicycles that, in turn move on circular orbits around the Earth? a. Copernican model. b. Tychonic model. c. Keplerian model. d. Ptolemaic model.

d. Ptolemaic model.

Which of the following astronomers is regarded as an early example of government-supported Big Science. a. Eratosthenes of Syene. b. Aristarchus of Samos. c. Copernicus. d. Tycho Brahe.

d. Tycho Brahe.

Aristarchus of Samos is known for a number of things. One of them was a. the idea that an explanation or model should 'save the appearances. b. his measurement of the size of the Earth. c. a model of the Solar System in which the Earth is fixed and everything rotates around the Earth. d. a model in which the Earth rotates on its axis and revolves around the Sun. e. the discovery that planets move on elliptical orbits around the Sun.

d. a model in which the Earth rotates on its axis and revolves around the Sun.

Retrograde Motion refers to the a. eastward motion of the Sun relative to the stars. b. westward motion of the Moon relative to the horizon. c. eastward motion of the planets relative to the stars. d. westward motion of the planets relative to the stars. e. westward motion of the planets relative to the horizon.

d. westward motion of the planets relative to the stars.

Ellipse

drawn by sticking two pins into a piece of paper and stretching a circular loop of string around both pins and the tip of a pencil. Moving the pencil so as to keep the loop stretched tight will cause it to draw an ellipse. ​The two pins are the foci of the ellipse.

Suppose a planet was discovered orbiting a star in a highly elliptical orbit. While the planet is close to the star it moves _____ but while it is far away it moves ____

faster;slower

Copernicus's model of the solar system was superior to Ptolemy's because

it had mathematical basis that could be used to predict the positions of planets

Ptolemaic Model​

the ancients assumed that each planet follows a small circular path (the epicycle) around a point (the deferent) which, in turn follows a circular path around the Earth.

retrograde motion

the apparent westward motion of the planets with respect to the stars planets appear to move westward for a period of time before resuming their normal eastward travel

synodic period

the period of rotation or revolution of a celestial body with respect to the sun

Perihelion

the point in the orbit of a planet, asteroid, or comet at which it is closest to the sun.

Aphelion

the point in the orbit of a planet, asteroid, or comet at which it is furthest from the sun.

cost-plus contracts

usually deals with something that has never been done before, so nobody knows what it will cost. the requirement is just to get something done, no matter what it will cost.

Tycho Brahe

was the first person to point out that whenever a comet appeared, observers all over Europe saw it in the same constellation. court astronomer to King Frederick II of Denmark attempted to measure all the planets, all the time, and more accurately than ever before could measure angles to 1/60 of a degree of arc