PHYS_1404: Solar System; CHP 2 HW

The most accurate Greek attempt to explain planetary motion was the model of:

Ptolemy

Which of the following is a contribution to astronomy made by Galileo?

- All of the Above

When would a new Venus be highest in the sky?

- At Noon Feedback: Correct. A new Venus occurs when Venus is directly between the Sun and Earth, which means a new Venus will be highest in the sky at the same time that the Sun is highest in the sky, which is around noon (local time).

The force of gravity varies with the

- Both A and C - The product of two masses - the inverse square of the distance separating the two bodies.

Observational proof of the heliocentric model: Astronomers have made many observations since the days of Galileo and Kepler to confirm that the Sun really is at the center of the solar system, and that the planets revolve around the Sun in elliptical orbits. Which observation(s) could you make today that Galileo and Kepler could not have made to confirm that the heliocentric model is correct?

- Doppler shifts in stellar spectra of nearby stars- Stellar parallax in nearby stars- Transit of an extrasolar planet Feedback: Correct. 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.

Kepler's second law implies what about planetary motion?

A planet moves faster when it is closer to the Sun.

Which was a contribution to astronomy made by Copernicus?

- He laid out the order and relative motion of the known solar system.

Galileo Galilei was the first scientist to perform experiments in order to test his ideas. He was also the first astronomer to systematically observe the skies with a telescope. Galileo made four key observations that challenged the widely accepted philosophical beliefs on which the geocentric model was based, thus providing support for the heliocentric model. 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. - The Sun has sunspots and rotates on its axis. - The Moon has mountains, valleys, and craters. - Venus goes through a full set of phases. Feedback: Correct. 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.

Kepler's contributions: Johannes Kepler used decades of Tycho Brahe's observational data to formulate an accurate description of planetary motion. Kepler spent almost 30 years of his life trying to develop a simple description of planetary motion based on a heliocentric model that fit Tycho's data. What conclusion did Kepler eventually come to that revolutionized the heliocentric model of the solar system?

- Kepler determined that the planetary orbits are elliptical. Feedback: Correct. 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.

Imagine that Venus is in its full phase today. If we could see it, at what time would the full Venus be highest in the sky?

- Noon Feedback: Correct. Because Venus is full when it is on the opposite side of the Sun from Earth, the Sun and Venus both appear to move through the sky together at that time. Venus therefore rises with the Sun, reaches its highest point at noon, and sets with the Sun.

Combining Newton's and Kepler's laws, we can weigh the Sun, provided we know:

- The size of the A.U. and the length of the year.

Each of the four diagrams below represents the orbit of the same comet, but each one shows the comet passing through a different segment of its orbit around the Sun. During each segment, a line drawn from the Sun to the comet sweeps out a triangular-shaped, shaded area. Assume that all the shaded regions have exactly the same area. Rank the segments of the comet's orbit from left to right based on the length of time it takes the comet to move from Point 1 to Point 2. Rank from longest to shortest. If you think that two (or more) of the diagrams should be ranked as equal, drag one on top of the other(s) to show this equality.

- They all over lap each other in the middle. (ADD all the figures on-top of each other in the diagram, they are all EQUAL)

In Ptolemy's Earth-centered model for the solar system, Venus's phase is never full as viewed from Earth because it always lies between Earth and the Sun. In reality, as Galileo first recognized, Venus is __________.

- full whenever it is on the opposite side of the Sun from Earth, although we cannot see the full Venus because it is close to the Sun in the sky. Feedback: Correct. A full Venus always occurs when it is on the opposite side of the Sun as viewed from Earth. (However, we cannot see the full Venus, because it is always very close to the Sun in the sky at that time.) Galileo used this fact as evidence for the Sun-centered view of the solar system: The fact that Venus goes through all the phases must mean it goes all the way around the Sun. In contrast, in the Ptolemaic model, Venus only varies between new and crescent phases.

Escape velocity is the speed required to:

- overcome the gravitational pull of an object.

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

When would you expect to see Venus high in the sky at midnight?

-Never Feedback: Correct. For Venus to be high in the sky at midnight, it would have to be on the opposite side of our sky from the Sun. But that never occurs because Venus is closer than Earth to the Sun.

In Ptolemy's Earth-centered model for the solar system, Venus always stays close to the Sun in the sky and, because it always stays between Earth and the Sun, its phases range only between new and crescent. The following statements are all true and were all observed by Galileo. Which one provides evidence that Venus orbits the Sun and not Earth?

-We sometimes see gibbous (nearly but not quite full) Venus. Feedback: Correct. In the Ptolemaic system, we should never see more than a crescent in Venus. Because we do in fact see more, the Ptolemaic model must be wrong. The full range of phases that we see for Venus is consistent only with the idea that Venus orbits the Sun. Galileo was the first to observe the phases of Venus — and hence to find this evidence in support of the Sun-centered system — because he was the first to observe Venus through a telescope. Without a telescope, we cannot tell that Venus goes through phases.

The major axis for a new comet has been determined to be 100 AU. The eccentricity of the orbit was measured to be 0.94. What is the distance of closest approach to the Sun for this comet?

3 AU

A vocabulary in context exercise in which students match words to definitions describing elliptical planetary orbits, applying ideas from Kepler's Laws of Planetary Motion.

ANSWERS LISTED IN THE NEXT FEW SECTIONS BELOW (ON QUIZLET). ↓↓↓↓

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

Aphelion

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

Ellipse

Which of these was a contribution of Newton to astronomy?

CORRECT - All of these were due to Newtons work. - Artificial satellites could be put into orbit about the Earth.- His differential calculus lets us calculate planetary motions more accurately.- The Sun's gravity is greatest on a planet at perihelion, so the planet must speed up.- The Moon pulls as strongly on us as we do on it.

While both Ptolemy and Copernicus assumed all orbits were ________, Kepler's first law corrected this and made planetary motion predictable.

Circles

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

Focus

Consider again the diagrams from Part A, which are repeated here. Again, assume that all the shaded areas have exactly the same area. This time, rank the segments of the comet's orbit from left to right based on the distance the comet travels when moving from Point 1 to Point 2. Rank from longest to shortest. If you think that two (or more) of the diagrams should be ranked as equal, drag one on top of the other(s) to show this equality.

For this diagram, look at the distance between the two blue dots. The bigger the space between the two dots, it is the longest. The smaller distances between the two dots, it is the shortest. Put them in order.

Consider again the diagrams from Parts A and B, which are repeated here. Again, assume that all the shaded areas have exactly the same area. This time, rank the segments of the comet's orbit based on the speed with which the comet moves when traveling from Point 1 to Point 2. Rank from fastest to slowest. If you think that two (or more) of the diagrams should be ranked as equal, drag one on top of the other(s) to show this equality.

For this one, SAME DIAGRAM AS ABOVE (OR THE QUESTION ANSWER BEFORE THIS ONE.) The fastest is the the greater distances between the two dots (or the shortest biggest area).. than put it in order... AGAIN SAME ANSWER AS QUESTION BEFORE THIS ONE.

The following five diagrams show pairs of astronomical objects that are all separated by the same distance d. Assume the asteroids are all identical and relatively small, just a few kilometers across. Considering only the two objects shown in each pair, rank the strength, from strongest to weakest, of the gravitational force acting on the asteroid on the left.

Left to Right - asteroid:sun - asteroid:earth - asteroid:moon - asteroid:asteroid - asteroid:hydrogen atom

Each of the following diagrams shows a spaceship somewhere along the way between Earth and the Moon (not to scale); the midpoint of the distance is marked to make it easier to see how the locations compare. Assume the spaceship has the same mass throughout the trip (that is, it is not burning any fuel). Rank the five positions of the spaceship from left to right based on the strength of the gravitational force that Earth exerts on the spaceship, from strongest to weakest.

Left to right Strongest- - Ship closet to the moon - 2nd closest to the moon - ship at midpoint - ship past midpoint - ship closest to the moon Shortest

The following diagrams are the same as those from Part A. This time, rank the five positions of the spaceship from left to right based on the strength of the gravitational force that the Moon exerts on the spaceship, from strongest to weakest.

Left to right; in order from the closest to the moon (strongest), than the closest to the earth (weakest). Strongest- - ship closest to the moon - Ship past the upper mid point - ship at midpoint -ship under midpoint (2nd closest to the sun.) - ship closest to the sun

Each of the following diagrams shows a planet orbiting a star. Each diagram is labeled with the planet's mass (in Earth masses) and its average orbital distance (in AU). Assume that all four stars are identical. Use Kepler's third law to rank the planets from left to right based on their orbital periods, from longest to shortest. If you think that two (or more) of the diagrams should be ranked as equal, drag one on top of the other(s) to show this equality. (Distances are to scale, but planet and star sizes are not.)

Longest -1 Earth Mass 2 AU & 3 Earth Masses 2 AU are SAME (Over lap these two figures in the diagram on the left (Longest). Shortest - 1 Earth Mass 1 AU & 2 Earth Masses 1 AU are SAME Shortest (Over lap these two figures int he diagram on the right (shortest).

Consider again the diagrams from Part D, which are repeated here. Again, imagine that you observed the asteroid as it traveled for one week, starting from each of the positions shown. This time, rank the positions from left to right based on the distance the asteroid will travel during a one-week period when passing through each location, from longest to shortest. If you think that two (or more) of the diagrams should be ranked as equal, drag one on top of the other(s) to show this equality.

Longest to Shortest. Longest is the comet closets to the sun. The comet at the bottom under the sun -> Comet at the lower right next to the sun -> The comet at the upper left -> The comet in front of the sun (opposite side from the sun).

Each of the four diagrams below represents the orbit of the same asteroid, but each one shows it in a different position along its orbit of the Sun. Imagine that you observed the asteroid as it traveled for one week, starting from each of the positions shown. Rank the positions based on the area that would be swept out by a line drawn between the Sun and the asteroid during the one-week period, from largest to smallest. If you think that two (or more) of the diagrams should be ranked as equal, drag one on top of the other(s) to show this equality.

Place all the figures together on the diagram. They are all EQUAL distances.

The following diagrams all show the same star, but each shows a different planet orbiting the star. The diagrams are all scaled the same. (For example, you can think of the tick marks along the line that passes through the Sun and connects the nearest and farthest points in the orbit as representing distance in astronomical units (AU).) Rank the planets from left to right based on their average orbital distance from the star, from longest to shortest. (Distances are to scale, but planet and star sizes are not.)

Rank it from the BIGGEST circle, to the SMALLEST circle, from left to right.

The following diagrams are the same as those from Part A. This time, rank the pairs from left to right based on the size of the acceleration the asteroid on the left would have due to the gravitational force exerted on it by the object on the right, from largest to smallest.

SAME AS ABOVE - asteroid:sun - asteroid:earth - asteroid:moon - asteroid:asteroid - asteroid:hydrogen atom

The following diagrams are the same as those from Part A. This time, rank the planets from left to right based on the amount of time it takes each to complete one orbit, from longest to shortest. If you think that two (or more) of the diagrams should be ranked as equal, drag one on top of the other(s) to show this equality. (Distances are to scale, but planet and star sizes are not.)

SAME AS ABOVE. Biggest circle to smallest circle.

Consider again the diagrams from Parts D and E, which are repeated here. Again, imagine that you observed the asteroid as it traveled for one week, starting from each of the positions shown. This time, rank the positions (A-D) from left to right based on how fast the asteroid is moving at each position, from fastest to slowest. If you think that two (or more) of the diagrams should be ranked as equal, drag one on top of the other(s) to show this equality.

SAME AS THE QUESTION ABOVE (OR THE QUESTION YOU JUST COMPLETED) . Fastest to slowest. Closest to the sun is the fastest, father away is the slowest. The comet at the bottom under the sun -> Comet at the lower right next to the sun -> The comet at the upper left -> The comet in front of the sun (opposite side from the sun).

The following diagrams are the same as those from Part A. Again considering only the two objects shown in each pair, this time rank the strength, from strongest to weakest, of the gravitational force acting on the object on the right.

SAME RANKING AS ABOVE. - asteroid:sun - asteroid:earth - asteroid:moon - asteroid:asteroid - asteroid:hydrogen atom

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

Semimajor Axis

The following diagrams show five pairs of asteroids, labeled with their relative masses (M) and distances (d) between them. For example, an asteroid with M=2 has twice the mass of one with M=1 and a distance of d=2 is twice as large as a distance of d=1. Rank each pair from left to right based on the strength of the gravitational force attracting the asteroids to each other, from strongest to weakest.

Strongest Force - d = 1, M = 2, M = 2 - d = 1, M = 1, M = 2 - d = 1, M = 1, M = 1 - d = 2, M = 1, M = 2 - d = 2, M = 1, M = 1 Weakest Force

The major axis for a particular planet is known. In order to determine the perihelion and the aphelion, what other information about the planet is needed?

The eccentricity of the orbit

The following diagrams are the same as those from Parts A and B. This time, rank the planets from left to right based on their average orbital speed, from fastest to slowest. If you think that two (or more) of the diagrams should be ranked as equal, drag one on top of the other(s) to show this equality. (Distances are to scale, but planet and star sizes are not.)

add figures to diagram. Smallest circle to the largest circle, left to right. (smaller the circle, the faster. the larger the circle the slower.)

The extent to which Mar's orbit differs from a perfect circle is ______.

eccentricity END OF KEY TERMS FOR QUESTION LISTED ABOVE.

Kepler's first law worked, where Copernicus' original heliocentric model failed, because Kepler described the orbits as:

elliptical, not circular.

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

perihelion

The place in a planet's orbit that is closest to the Sun is called

perihelion

According to Kepler's third law, the square of the planet's period in years is:

proportional to the cube of its semimajor axis in A.U.

Today we rely largely on what technique to precisely measure distances in the solar system?

radar echo timings