Astronomy At Play in the Cosmos; Chapter 3

Second Law of Planetary Motion

The line connection a planet to the Sun will sweep out equal areas of its orbit in equal times.

Which of Galileo's observations disputed the perfect nature of the heavens above the sublunar region?

Mountains on the Moon and Galilean moons.

The Inertial Law

Newton's first law states that objects in motion at constant velocity along a straight line stay that way unless acted on by a net force. Objects at rest stay at rest unless acted on by a net force.

A gun recoils when it fires. Which principle does this example most clearly illustrate?

Newton's law of reaction.

An astronaut is traveling in deep space far from any star or planet. To change his course he must fire his rockets. Which principle does this example most clearly illustrate?

Newton's law of reaction.

The Force Law

Newton's second law states that the change in an objects acceleration due to an applied net force is in the same direction as the force and directly proportional to it, but inversely proportional to the objects mass. Sometimes called the inverse law: if you double the distance between two , the force between them drops by 2 to the 2 = 4. If you increase the distance between the objects by a factor of 3, the force drops off by a factor of 3 to the 2 = 9.

The Reaction Law

Newton's third law states that for every applied force, there us an equal and opposite force.

In the law of gravity, G is...

A constant related to the strength of the gravitational force.

Tycho Brahe

Born Dec. 14, 1546 Died Oct. 24, 1601 Danish astronomer whose work developing astronomical instruments and in measuring and fixing the positions of stars paved the way for future discoveries. His accurate observations included a comprehensive study of the solar system and accurate positions of more than 777 fixed stars.

Sir Isaac Newton

Born Dec. 25, 1642 Died March 20, 1727 English physicist and mathematician. In optics, his discovery of white light integrated the phenomena of colors into the science of light and laid the foundation for modern physical optics. His 3 laws of motion resulted in the formulation of the law is universal gravitation. In math, he was the original discoverer of calculus.

Johannes Kepler

Born Dec. 27, 1571 Died Nov. 15, 1630 German astronomer who discovered three laws of planetary movement. Kepler did not, however, call them laws. He called them celestial harmonies that God designed for the Universe. Helped to push Copernicus' Sun-centered model.

Galileo Galilei

Born Feb. 15, 1564 Died Jan. 8, 1642 Italian physicist and astronomer. Improved the telescope and was the first to use it for astronomy. The telescope allowed him to observe the moons of Jupiter, the rings of Saturn, the phases of Venus, sunspots, and rugged lunar surfaces. Advocate of heliocentric universe. In 1633, he was placed under house arrest for the rest of his life by the Catholic Church.

Nicolaus Copernicus

Born Feb. 19, 1473 Died 1543 1508 - Developed his own celestial model of a heliocentric planetary system. His book, De Revolutionibus Orbium Coelestium was banned by the Catholic Church.

Foci (Focus)

Either of two points interior to and ellipse that are used to define its shape. The Sun is always at one focus of a planet's elliptical orbit.

Which of the following statements is/are true about velocity when considering a planet radius of R and a spaceship that will either orbit just above the planet's surface or attempt to escape the planet?

Escape velocity is always greater and the differ by a factor of the square root of 2.

Which of the following describes Kepler's approach and contributions to astronomy?

He constrained his models of planetary motion with the positional data from Tycho Brahe.

Which of the following does NOT describe a contribution that Galileo made to science?

He theorized that there was a mutually attractive force proportional to distance to explain how and why planets orbit the Sun.

Tycho Brahe is noted for many achievements EXCPT...

Innovative use of the telescope.

What is the effect on the force of gravity between two objects if the mass of one object remains unchanged while the distance to the second object and the second object's mass are both doubled?

It always decreases.

Ptolemy's model of the universe was accepted as valid for over a thousand years. Which of these is NOT one of the reasons for it's acceptance?

It correctly put the Sun at the center

Given two objects, if the mass of one increases while the distance between then increases, how does the magnitude if the gravitational force change?

It depends on the specific values of the mass and distance changes.

Two moons orbit a much larger planet. Moon A orbits at radius X. Moon B orbits at radius 4X. How does the planet's pull of gravity on each moon compare?

It is 16 times weaker for moon B.

Which of the following statements is true regarding Kepler's third law?

It says that the period and size of an orbit are correlated.

A spinning figure skater spins faster as he brings his outstretched arms inward. This is an illustration of the physical principle underlying:

Kepler's second law.

Which of the following values is/are the same whether one is standing on the Earth or on the Moon?

One's mass and the value of G.

Which of the following statements is consistent with Kepler's second law?

Planets always move faster when they are close to the Sun than when they are farther away.

First Law of Planetary Motion

Planets move on elliptical orbits with the Sun at one focus.

Which of the following statements about ellipses is true?

Semimajor and semiminnor axes are never equal and a circle is a form of ellipse.

Two ellipses have the same semimajor axes but different eccentricities. Which of the following statements is true?

The area inside the ellipse with the smaller eccentricity is smaller and one ellipse may be a circle.

Which of the following characteristics was/were included in Ptolemy's model of the Universe?

The celestial sphere is perfect and unchanging and the nested set of crystalline, celestial spheres is maintained as proposed by Aristotle.

Galilean Moons

The four largest moons of Jupiter (Io, Europa, Ganymede, and Callisto). They were discovered by Galileo Galilei around Jan. 1610 and were the first group of objects found to orbit another planet. Their names are the names of Zeus' lovers. Their orbits range from 16.7 days (outermost Callisto) to 1.8 days (innermost Io).

Of which of the following was the Copernican model correct according to our current knowledge?

The placement of the Sun at the center and the shape of planetary orbits.

Third Law of Planetary Motion

The square of a planet's orbital period equals its average orbital radius cubed.

Orbital Period

The time it takes for a planet to complete one cycle around the Sun. Earth's period is one year. Mars' period is 1.88 years.

Planetary Revolution

The time it takes to complete one orbit.