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GVSU / Physics / PHYS 105 / Who proposed the geocentric view that was accepted and used for more t

Who proposed the geocentric view that was accepted and used for more t

Who proposed the geocentric view that was accepted and used for more t

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Astronomy Exam 2 Study Guide Merillat


Who proposed the geocentric view that was accepted and used for more than 18 centuries?



Vocab from Chapter 1 

∙ Acceleration- The rate of change of velocity of a moving object. ∙ Aphelion- The point on the elliptical path of an object in orbit about  the Sun that is most distant from the Sun.

∙ Astronomical unit (AU)- The average distance of Earth from the Sun.  Precise radar measurements yield a value for the AU of 149,603,500  km.

∙ Center of mass- The “average” position in space of a collection of  massive bodies, weighted by their masses. For an isolated system this  point moves with constant velocity, according to Newtonian  mechanics.

∙ Copernican revolution- The realization, toward the end of the 16th  century, that Earth is not at the center of the universe.


What is the name given to the phenomenon in which the apparent motion of the superior planets sometimes reverses?



∙ Deferent- A construct of the geocentric model of the solar system that was needed to explain observed planetary motions. A deferent is a  large circle encircling Earth, on which an epicycle moves. Don't forget about the age old question of Who is responsible for creating a new instance of a class?

∙ Eccentricity- A measure of the flatness of an ellipse, equal to the  distance between the two foci divided by the length of the major axis. ∙ Ellipse- Geometric figure resembling an elongated circle. An ellipse is  characterized by its degree of flatness, or eccentricity, and the length  of its long axis. In general, bound orbits of objects moving under  gravity are elliptical.

∙ Epicycle- A construct of the geocentric model of the solar system that  was necessary to explain observed planetary motions. Each planet  rides on a small epicycle whose center in turn rides on a larger circle  (the deferent).


How did ptolemy's model explain the retrograde motions of the planets?



∙ Force- Action on an object that causes its momentum to change. The  rate at which the momentum changes is numerically equal to the  force.

∙ Geocentric model- A model of the solar system that holds that Earth  is at the center of the universe and all other bodies are in orbit around  it. The earliest theories of the solar system were geocentric.

∙ Gravitational force- Force exerted on one body by another due to the effect of gravity. The force is directly proportional to the masses of both bodies involved and inversely proportional to the square of the  distance between them. If you want to learn more check out What is the most popular music in the dominican republic?

∙ Gravity- The attractive effect that any massive object has on all other  massive objects. The greater the mass of the object, the stronger its  gravitational pull. If you want to learn more check out How does the criminal justice system perpetuate racial inequality?

∙ Heliocentric model- A model of the solar system that is centered on  the Sun, with Earth in motion about the Sun.

Astronomy Exam 2 Study Guide Merillat

∙ Inertia- The tendency of an object to continue moving at the same  speed and in the same direction, unless acted upon by a force. ∙ Inverse-square law- The law that a field follows if its strength  decreases with the square of the distance. Fields that follow the  inverse-square law decrease rapidly in strength as the distance  increases, but never quite reach zero.

∙ Laws of planetary motion- Three laws derived by Kepler describing  the motion of the planets around the Sun. If you want to learn more check out Define attachment.

∙ Mass- A measure of the total amount of matter contained within an  object.

∙ Newtonian mechanics - The basic laws of motion postulated by  Newton, which are sufficient to explain and quantify virtually all of the  complex dynamical behavior found on Earth and elsewhere in the  universe.

∙ Orbital period- Time taken for a body to complete one full orbit  around another.

∙ Perihelion- The closest approach to the Sun of any object in orbit  about it.

∙ Ptolemaic model- Geocentric solar system model, developed by the  second century astronomer Claudius Ptolemy. It predicted with great  accuracy the positions of the then known planets.

∙ Radar- Acronym for Radio Detection And Ranging. Radio waves are  bounced off an object, and the time taken for the echo to return  indicates its distance.

∙ Retrograde motion- Backward, westward loop traced out by a planet  with respect to the fixed stars. We also discuss several other topics like What causes natural unemployment rates to change?

∙ Semimajor axis- One-half of the major axis of an ellipse. The  semimajor axis is the way in which the size of an ellipse is usually  quantified.

Review Q’s & A’s From The Homework 

∙ Who proposed the geocentric view that was accepted and used for  more than 18 centuries?  

o Aristotle

∙ What was the primary reason Copernicus proposed a heliocentric  model for the solar system?

o It was much simpler than the Ptolemaic model

∙ What is the name given to the phenomenon in which the apparent  motion of the superior planets sometimes reverses?

o Retrograde motion

∙ How did Ptolemy's model explain the retrograde motions of the  planets?We also discuss several other topics like How are seeds so successful?

Astronomy Exam 2 Study Guide Merillat

o Planets orbit in small circles called epicycles, and the epicycle is  orbiting the Earth in a larger orbit called a deferent. This caused  the planet to have a "looping" motion as seen from Earth.

∙ How did Copernicus' model explain the retrograde motions of the  planets?

o Planets orbit the Sun at different speeds. When an inner, faster moving planet "passes" a slower outer one, the slower planet  appears to move backwards.

∙ According to Copernicus, retrograde motion occurs at opposition for  the outer planets.

o True

∙ Which model used circular deferments and epicycles in a geocentric  universe to explain planetary motions?

o Ptolemy Model

∙ _____'s theories were based on the very accurate observations made by _____.

o Kepler, Tycho Brahe

∙ Aristotle proposed that all planets revolve around the Sun. o False- Aristotle was responsible for the geocentric model of the  solar system, which portrayed earth in the center.

∙ During retrograde motion, planets actually stop and move backwards  in space.

o False- they only appear that way.

∙ The heliocentric model of the universe holds that Earth is at the center  and everything else moves around it.

o False- The heliocentric model features the sun at the center. ∙ A major flaw in Copernicus's model was that it still had… o Circular Orbits

∙ Which of the following was NOT one of the discoveries made by  Galileo?

o The shape of a planet’s orbit is an ellipse. Kepler made that  discovery.

o Galileo’s discoveries consisted of (1) the moon having  mountains, valleys, and craters. (2) The sun’s rotation and sun  spots (3) Jupiter having it’s own moons.

∙ Galileo's observations of the phases of Venus ________. o Showed that Venus had to orbit the Sun and not the Earth ∙ Among Galileo's discoveries with his telescope were sunspots. o True

∙ Galileo's observations of the entire phase cycle of Venus proved that  Ptolemy's epicycles could not be correct in keeping Venus between us  and the Sun.

o True

Astronomy Exam 2 Study Guide Merillat

∙ A fatal flaw with Ptolemy's model is its inability to predict the observed  phases of…

o Mercury and Venus

∙ Galileo found the rotation period of the Sun was approximately… o A month

∙ Copernicus's theories gained widespread scientific acceptance during  his lifetime.

o False- almost all appreciation of scientists discoveries happen  after they die.

∙ Galileo's observations of the sky were made with the naked eye. o False- Galileo was one of the earliest astronomers to make  observations using a telescope.

∙ Kepler's third law is best expressed as ________.

o P 2 ~ a 3

∙ How does orbital speed at aphelion compare to the speed at  perihelion?

o Lower (the speed decreases with distance to the sun, and the  aphelion is a planets furthest possible distance from the sun  while in orbit.)

∙ Kepler's second law of planetary motion states that a planet in orbit  around the Sun will do which of the following?

o Sweep out equal areas in equal times

∙ What was the greatest contribution of Tycho Brahe to astronomy? o He amassed a large number of precise measurements of stellar  and planetary positions in the sky.

∙ What two measurable properties directly tell us the size and shape of a planet's orbit?

o Semimajor axis and eccentricity. (These are two primary  characteristics of an orbit.)

∙ An Astronomical Unit (AU) is …?

o the average distance between the Sun and Earth.

∙ Kepler's third law allows us to find the average distance to a planet  from observing its period of rotation on its axis.

o False- axis rotation is not the determining factor of distance,  however Kepler’s third law will tell us how to measure the  masses of any celestial object.

∙ According to Kepler's third law, if you know the planet's orbital period,  you can find its average distance from the Sun.

o True

∙ A planet (or comet) will speed up as it approaches the Sun. o True

∙ Kepler found the orbits of planets are ellipses, not circles. o True

Astronomy Exam 2 Study Guide Merillat

∙ Kepler relied heavily on the telescopic observations of Galileo in  developing his laws of planetary motion.

o False- The telescope was not yet invented in Keple’r time. He  based all of his theories through naked eye observations made  by his partner in work, Tycho Brahe.

∙ Kepler's third law relates the square of the planet's orbital period in  years to the cube of its average distance from the Sun in astronomical  units.

o True

∙ Tycho Brahe's contribution to Kepler's Laws of Planetary Motion were,,, o his detailed and accurate observations of the planets' positions. ∙ When a planet's orbit takes it closest to the Sun, it's called… o Perihelion

∙ A planet whose distance from the Sun is 3 AU would have an orbital  period of how many Earth-years?

o Square root of 27

∙ Whose three laws of planetary motion allowed us to predict planetary  motion?

o Kepler

∙ The speed of a planet orbiting the Sun is independent of the planet's  position in its orbit.

o False- planet’s speed is faster when closest to the sun and slower while furthest away from the sun.

∙ Kepler's laws hold only for the six planets known in his time. o False- Kepler’s laws were modified and tested during his lifetime  and can still apply to all known planets currently.

∙ A calculation of how long it takes a planet to orbit the Sun would be  most closely related to Kepler's

o Third law of planetary motion.

∙ If Earth’s orbit around the Sun were to double in size, the new “year”  would be…

o more than 2 current Earth years.

∙ Earth is located at one ____ of the Moon's orbit.  

o Focus

∙ According to Kepler's second law, Jupiter will be traveling most slowly  around the Sun when at ____.

o Aphelion.  

∙ Earth orbits in the shape of a/an ____ around the Sun. o Ellipse

∙ The mathematical form of Kepler's third law measures the period in  years and the ________ in astronomical units (AU).

Astronomy Exam 2 Study Guide Merillat

o Semimajor axis

∙ According to Kepler's second law, Pluto will be traveling fastest around  the Sun when at _______.

o Perihelion

∙ The extent to which Mars' orbit differs from a perfect circle is called its ________.

o Eccentricity  

∙ Which of the following is NOT one of Newton's Laws of Motion? o The orbital paths of the planets are elliptical (not necessarily  circular), with the Sun at one focus. (this is Kepler’s first law). ∙ According to Newton, planets orbit in ellipses with what at the two foci? o The center of mass and nothing. (Newton recognized that two  orbiting bodies orbit in ellipses with their common center of mass at one focus and nothing at the other focus.)

∙ In what way did Newton improve Kepler's laws?

o He discovered the dependence on mass in the third law. ∙ The force of gravity between two objects obeys which of the following  relationships?

o It is attractive and increases if their masses increase. ∙ If the distance between the centers of two objects doubles, what  happens to the gravitational pull between them if the masses do not  change?

o The force will decrease to one-fourth its previous size. (Inverse  Square Relationship)

∙ According to Newton's third law, when the Voyager probes passed  Jupiter in 1979, they exerted exactly the same force on Jupiter as the  giant planet did on them.

o True

∙ Compared to when it was on the surface, a satellite in an orbit whose  radius is about 4 times the Earth's radius will experience about 1/16  the force due to the Earth's gravity.

o True

∙ According to Newton's second law, if you double the force acting on a  body, the acceleration will double.

o True

∙ A circular orbit would have an eccentricity of…?

o Zero

∙ How much stronger is the gravitational pull of the Sun on Earth, at 1  AU, than it is on Saturn at 10 AU?

o One hundred

∙ If the distance between two asteroids is doubled, the gravitational  force they exert on each other will…?

o Be one fourth as great

Astronomy Exam 2 Study Guide Merillat

∙ According to Newton's laws, the planets orbit the Sun due to _____. o Gravity

∙ Retrograde motion was explained by the Greeks by inventing which of  the following?

o Telescope

∙ In the geocentric Greek model, which of the following objects did not  require an epicycle?

o Sun

∙ Which of the following is the best summary of Galileo's observations of  the phases of Venus that directly refuted the Ptolemaic (geocentric)  model?

o Venus can be seen to exhibit a full phase, which is predicted not  to happen in the geocentric model.

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