Astronomy Chapter 3

newton's laws

1. object remains at rest (or in motion at constant velocity) unless acted on by a force 2. a=F/m acceleration = force/mass 3. to every action, there is an equal opposite reaction discovered dependence on mass elliptical orbits with center of mass and nothing as foci

kepler's laws

1. planetary orbits are elliptical, don't move in uniform motion 2. sweep out equal areas in equal times 3. period^2 divided by radius^3 = constant for each planet p^2 = a^3 (semimajor axis in AU)

In which of the following ways do Pluto and Eris differ from the terrestrial and jovian planets in our solar system

Both Pluto and Eris are smaller than any of the terrestrial planets. Both Pluto and Eris travel in more elliptical orbits than any of the terrestrial or jovian planets. Both are less massive than terrestrial and jovian planets

heliocentric model

Copernicus: still used epicycles retrograde explained by orbital speeds of planets sun-centered explained motion adn brightness changes most simply used parallax as explanation

newton's law of universal gravitaion

F=G(mass1 times mass2/r^2) r=distance further distance, weaker force: F proportional to 1/r^2 higher mass, higher force

In what way did Newton improve Kepler's laws?

He discovered the dependence on mass in the third law.

Which of the following is NOT true about the solar system model of Copernicus?

It used elliptical orbits for the motions of the planets. IS TRUE Its central organizing principle and primary attraction to Copernicus were that it was simpler to comprehend than the Ptolemaic model. It used an earlier Greek idea that placed the Sun at the center of the solar system. It was not widely accepted and was not even published until the year that he died. It could explain apparent retrograde motion by showing that fast-moving inner planets "passed" slowewr outer planets as they went around the Sun. Although Copernicus placed the Sun at the center of the solar system with the planets orbiting it instead of Earth, he assumed that planets moved in perfect circular orbits. He retained the ideas of epicycles and deferents to allow for small adjustments to the rates at which the planets orbited the Sun. These ideas were abandoned only after Kepler introduced the idea of elliptical orbits much later.

...is the jovian planet that orbits closest to the Sun.

Jupiter

The planet with the lowest average density is

Saturn

Which observation(s) could you make today that Galileo and Kepler could not have made to confirm that the heliocentric model is correct?

Stellar parallax in nearby stars Transit of an extrasolar planet Doppler shifts in stellar spectra of nearby stars When Galileo observed the changing phases of Venus, he showed that at least one planet must be orbiting the Sun. Today, astronomers are confident that all of the planets in our solar system orbit the Sun because of Earth-based observational evidence that supports a heliocentric model. Doppler shifts and stellar parallaxes show that Earth is in motion around the Sun and is thus not stationary. More recent observations of extrasolar planets show astronomers that planets in other planetary systems are orbiting stars.

Assuming that other planetary systems form in the same way as our solar system formed, where would you expect to find terrestrial planets?

Terrestrial planets will likely be located nearer the planetary system's star than any jovian planets. Based on what we find in our own solar system, we expect terrestrial planets to form close to a star and jovian planets to form farther out.

Why, then, was the geocentric model the leading theory for such a long time, even though the heliocentric model more simply explained the observed motions and brightness of the planets?

The heliocentric model did not make noticeably better predictions than the geocentric model. Ancient astronomers did not observe stellar parallax, which would have provided evidence in favor of the heliocentric model. The geocentric model conformed to both the philosophical and religious doctrines of the time. From Earth, all heavenly bodies appeared to circle around a stationary Earth. The geocentric model was the leading model for hundreds of years because it conformed to the common beliefs from observations and religious doctrine of the time. However, the heliocentric model gained widespread acceptance when astronomers obtained new evidence after the time of Copernicus. These astronomers popularized his view and helped pave the way for our current understanding of the solar system.

An accurate sketch of Jupiter's orbit around the Sun would show

a nearly perfect circle

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

aphelion

a major flaw in copernicus' model was that it still had

circular orbits

terrestrial planets

closer to system's star solid, rocky surface small size mercury, venus, mars, earth

geocentric model

earth-centered retrograde explained by epicycles (Ptolemy) rooted in religious beliefs all heavenly bodies appeared to circle earth

most of the surface of...is covered with liquid water

earthj

the extent to which Mars' orbit differs from a perfect circle is called its

eccentricity

Earth orbits in the shape of a/an..around the sun

ellipse

T/F During retrograde motion, planets actually stop and move backward in space.

false

T/F: Aristotle proposed that all planets revolve around the sun

false

T/F: Kepler's laws hold only for the 6 planets during his time

false

T/F: The solar system is of largely uniform composition

false

If the Sun and its mass were suddenly to disappear, Earth would

fly off into space

earth is located at one...of the moon's orbit

focus

jovian planets

generally more massive, lower in average density extensive ring systems numerous orbiting moons mainly H, He compounds jupiter, saturn, uranus, neptune

Geocentric vs Heliocentric

geocentric: This model is Earth-centered. Retrograde motion is explained by epicycles. Rooted in widely accepted religious beliefs regarding Earth's place in the universe heliocentric: Retrograde motion is explained by the orbital speeds of planets. This model is Sun-centered. Explained planetary motions and brightness changes most simply both: Planets move in circular orbits and with uniform motion. The brightness of a planet increases when the planet is closest to Earth. Epicycles and deferents help explain planetary motion. Predicted planetary positions accurately over relatively short time periods Planetary orbits and motions based on Greek ideologies of perfect form and motion Ptolemy's geocentric model was based on the idea that Earth is the center of the universe, while Copernicus's heliocentric model was developed around the idea that the Sun is at the center. While these two models were based on opposing ideas, they shared a common belief in uniform circular motion and the use of epicycles. However, Copernicus's heliocentric model does not use epicycles to explain retrograde motion like Ptolemy's geocentric model. In order to explain retrograde motion, Copernicus uses the different orbital speeds of the planets as an explanation to the seemingly backward motion of the planets in the sky. The geocentric model was compelling because it adhered to religious beliefs about Earth's centrality in the universe. The heliocentric model was compelling because it provided a simpler explanation for observed motions in the solar system. Because both models adhered to the belief in perfect form and motion, they made inaccurate predictions of planetary motions over long periods of time. Since neither model made better predictions than the other, both remained viable.

An asteroid with an orbit lying entirely inside Earth's

has an orbital semimajor axis of less than 1 AU

What conclusion did Kepler eventually come to that revolutionized the heliocentric model of the solar system?

he determined that the planetary orbits are elliptical One of the most crucial conclusions that Kepler reached using Tycho's data was that the planets do not move in circular orbits, but rather in elliptical orbits. Kepler also concluded that the planets do not move with uniform motion. Applying these ideas to the Copernican model, the revised heliocentric model could then accurately predict planetary positions over long periods of time.

galileo observations

jupiter has orbiting moons moon has mountains, valleys, craters, venus goes through phases, sun has spots and rotates on axis

From the following list of observations, which are the key observations made by Galileo that challenged widespread philosophical beliefs about the solar system?

jupiter has orbiting moons, moon has mountains, valleys, and craters, venus goes through a full set of phases, the sun has sunspots and rotates on its axis Galileo made four key observations that went against the geocentric model and the common beliefs about the universe at the time. Observing that the Sun and Moon had surface blemishes disproved the idea that celestial objects were perfect. Galileo's observations of Jupiter's orbiting moons showed that there were other centers of motion in the universe. Galileo's most crucial observation was the observation of Venus in different phases, which directly supported the idea that objects orbit the Sun rather than Earth.

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

lower

Which of the following is NOT a characteristic of terrestrial planets?

lower density than jovian planets TRUE Weaker magnetic fields than jovian planets Smaller radii than jovian planets Closer to the Sun than jovian planets

The only rocky planet to have more than one moon is

mars

the planet that orbits closest to the sun is

mercury

A planet's mass can most easily be determined by measuring the planet's

moon's orbits

Compared to terrestrial planets, jovian planets are __________.

more massive and lower in average density Note that while jovian planets are lower in average density than terrestrial planets, the densities in their deep interiors are quite high, in some cases higher than the densities found at the centers of the terrestrial worlds.

..is about 30 times as far from the Sun as our own planet.

neptune

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

perihleion

Which of the major planets listed below has the highest mass?

saturn Saturn is the second-largest planet in the solar system, and also the second-heaviest, after Jupiter.

he mathematical form of Kepler's third law measures the period in years and the...in AU

semimajor axis

solar system

sun, mercury, venus, earth, mars, asteroid belt, jupiter, saturn, uranus, neptune, pluto

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

sweep out equal areas in equal times

According to Newton, planets orbit in ellipses with what at the two foci?

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.

Consider Earth and the Moon. As you should now realize, the gravitational force that Earth exerts on the Moon is equal and opposite to that which the Moon exerts on Earth. Therefore, according to Newton's second law of motion __________.

the moon has a larger acceleration than earth, because it has a smaller mass Newton's second law of motion, F=ma, means that for a particular force F, the product mass x acceleration must always be the same. Therefore if mass is larger, acceleration must be smaller, and vice versa.

How does the parallax of a nearby object compare to that of an object farther away?

the nearby object exhibits a larger parallax than the farther object parallax is inversely related to distance

Which of the following was not one of the discoveries made by Galileo?

the shape of an orbit is an ellipse (kepler)

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

true

T/F: The total mass of all the planets is much less than the mass of the Sun.

true

T/F: You throw a baseball to someone, before the ball is caught, it is temporarily in orbit around the Earth's center

true

...has a rotational axis that is tilted so much it lies nearly in the plane of its orbit.

uranus

If we were to construct an accurate scale model of the solar system on a football field with the Sun at one end and Neptune at the other, the planet closest to the center of the field would be

uranus

Which planet is approximately halfway between Pluto's orbit and the Sun?

uranus

...is the planet with the highest average surface temperature.

venus

Was it possible for the geocentric system of Ptolemy to explain the observed retrograde motion of the planets?

yes, through a system of epicycles and deferents The Ptolemaic system of epicycles and deferents survived for nearly 1300 years and was used as a practical, although complicated, system for calculation and prediction of planetary motions. It failed eventually on entirely different evidence, but was able to explain and predict the retrograde motion of the planets.