Astronomy chapter 2

Planets normally move from the west to the east with respect to the stars. Occasionally, they move east to west for a few weeks, which is called _____motion.

retrograde

Select the objects that complete the sentence: For a planetary orbit, ___ is found at one focus of the ellipse and ____ is found at the other focus

the Sun nothing

Eratosthenes's calculation of the size of Earth required that the Sun be very far away from us because ____.

the rays of sunlight only arrive at Earth in parallel lines if the Sun is far away from us

If the Moon were three times farther away from us than it now is, its angular size would be

three times smaller.

If the Sun's true diameter were twice as large as it is now, it's angular size would be

twice as big.

Put the following discoveries in chronological order, starting with the work of Copernicus (at the top), followed by Tycho Brahe, Galileo, and Newton (at the bottom).

1. Earth is the center of the Solar System. 2. Exploding stars are not part of the Solar System. 3. Jupiter has its own moons. 4. The law of gravity

Arrange the steps of Eratosthenes's calculation of the size of Earth.

1. On the summer solstice, obtain the angle of a shadow cast at noon in Alexandria as 7 degrees. There is no shadow cast in syene. 2. Sun's rays arrive at Earth as parallel lines. Use the measurement to show the angular separation on Earth's surface of Alexandria and syene is 7 degrees. 3. Substitute values in anglebetween cities/360degrees= distance between cities/earth's circumference. 4.Solve the equation to calculate the circumference of Earth.

Place the celestial bodies in their order of increasing distance from Earth in the geocentric model of the Solar System.

1. The moon 2. Mercury 3. Venus 4. The sun 5. Mars 6. Jupiter, then Saturn

Although he did not believe in the heliocentric model (he proposed his own hybrid model), arrange the statements to summarize how Tycho Brahe contributed to the eventual understanding of the Solar System as heliocentric.

1. Tycho had an intense passion for studying astronomy. 2. Tycho designed and built the most accurate observational tools up to that date. 3.Tycho made the most precise measurements of planetary positions. 4. Tycho's meticulous observations were used to show the true shape of planetary orbits. 5. With the right orbital shape, the heliocentric model accurately predicts planetary motions.

Select all the science-based reasons the ancient Greeks had for thinking that Earth is round. (Select all that apply.)

A traveler who moves south will see different stars than one who stays up north. The shadow of Earth on the Moon is round.

Which ancient Greek astronomer used shadows cast by the Sun to estimate the size of Earth?

Eratosthenes

True or false: Planets orbit the Sun on circular-shaped orbits.

False Reason: Copernicus thought the orbits were circles, but Kepler showed they are really ellipses.

True or false: The work of Islamic scholars had a big influence on the astronomical discoveries of the ancient Greek scientists.

False: Islamic civilization reached its peak hundreds of years after ancient Greece.

True or false: An object with a large angular diameter will always have a large true diameter.

False: No, large angular diameter means the object looks big. It could be something very small that is just very close to us, or it could be a very large object that is farther away.

Aristarchus was a Greek astronomer who surmised that Earth orbited the Sun. Make the argument of Aristarchus's critics by matching steps with the scientific method.

Form a hypothesis: Earth moves around Sun. Propose a test.: An orbiting planet will see objects shift position depending on their distance (parallax). Collect new data.: No parallax is observed. Accept or deny the hypothesis.: Earth must be stationary.

Select all that correctly describe Ptolemy.

He lived in the Egyptian city of Alexandria. He wrote a book called Almagest that summarized ancient Greek knowledge of astronomy. He was an influential astronomer in the Roman Empire.

How did Galileo demonstrate that the sky was not perfect and unchanging, as people had believed it to be?

He observed sunspots, which look like blemishes and change their positions from day to day.

Why did the Catholic Church put Galileo on trial?

His support of a heliocentric model was contrary to Church teachings.

In a solar system very similar to ours, an Earth-like planet orbits a star just like the Sun. This planet has an orbital period two-thirds that of Earth's. How will its average distance from the star be different?

It will orbit closer to its star than we do from the Sun.

Select all that correctly describe the Moon illusion.

It's an optical illusion. It makes the Moon seem larger closer to the horizon.

To calculate the true diameter of a planet, what information do you need? (Select all that apply.)

Its angular diameter Its distance

Which of the following laws states that a line from the planet to the Sun sweeps out equal areas in equal times?

Kepler's second law

Select all of the following that were important astronomical contributions made by Tycho Brahe.

Making very accurate measurements of planet positions Observing a supernova and showing it had a fixed position, so it was far beyond the planets Discovering that comets are in space, not in Earth's atmosphere

How does the heliocentric model of Copernicus explain the retrograde motion of Mars?

Mars takes longer to complete its orbit than Earth, so when we pass it, it falls behind us and appears to move backwards.

In Ptolemy's model, Venus does not go through a complete set of phases (which it does in reality). Which other planet does not go through all the phases in Ptolemy's model but does in Copernicus's model?

Mercury

Match the correct famous scientist to each discovery.

Newton -Calculus -Law of gravity Galileo -Jupiter has moons -Venus has phases Kepler -Elliptical orbits Tycho -Comets are in space

The idea that scientific models must be as simple as possible and still explain what is known about a phenomenon is called ____.

Ockham's razor

Select Kepler's three laws of planetary motion from the following list.

Planets move faster in their orbits when close to the Sun and slower when far from it. Planets move in elliptical orbits with the Sun at one focus. p2 = a3

Select all the apparent planetary motions that are not a result of Earth's rotation.

Planets move west to east with respect to the stars. Planets occasionally move backwards across the sky. Planets always stay very close to the ecliptic.

Match each model of the Solar System with its description.

Ptolemy's model:The Sun, Moon, planets, and stars all move around Earth on small circles (epicycles) attached to larger ones (orbits). Tycho's model: The Sun moves around Earth and other planets move around the Sun. Copernicus's model: Earth and all the other planets move around the Sun.

Select all the statements about Ockham's razor that are correct.

Scientific models should be as simple as possible in order to explain all the phenomena. It's okay to make a model more complex as long as it predicts results better than a simpler model could.

Select all the reasons that explain how Galileo's discovery of sunspots showed that the sky was not perfect and unchanging?

Sunspots change position from day to day, and even disappear. Sunspots look like blemishes, and the Sun was thought to be perfect.

Match Galileo's discoveries with the reasons they support Copernicus's model of the Solar System.

The Moon has mountains.>>Objects in space were real and made of materials like Earth; they were not ethereal substances with exotic properties. Jupiter has moons.>>Earth is not the center of the Solar System (or the Universe). Venus has phases like the Moon.>>Planets orbit the Sun, not Earth.

Select all of the objects for which Aristarchus estimated the distance.

The Sun The Moon

Select all of the objects for which Aristarchus estimated the size, relative to Earth.

The Sun The Moon

Select the properties of Eudoxus (an ancient Greek) geocentric model of the solar system.

The Sun and Moon move around Earth. The planets move around Earth. Objects closest to Earth move fastest.

According to Aristarchus, if the Sun were just a few times farther from Earth than the Moon is, how would the Sun and the Moon look relative to each other at the time of third quarter?

The angle between them would be much less than 90°.

How would the angle between Alexandria, Earth's center, and Syene change if the distance between them were 1000 stadia instead of 5000 stadia?

The angle would be smaller.

Why do the planets always remain close to the ecliptic?

The planets all go around the Sun with orbits roughly all in the same plane.

Select all of the following that are parts of Ptolemy's geocentric model.

The planets, the Sun, and the Moon move around Earth. The stars are farther away than the planets. Planets move on small circles called epicycles.

In Ptolemy's model of the Solar System, what would be different about a planet with a large epicycle versus one with a small epicycle?

The size of the "zig-zag" during retrograde motion would be bigger and last longer for a larger epicycle.

Under what circumstances would you measure a large parallax for a star?

The star is very close to Earth.

The ancient Greeks knew about parallax, so why did Aristarchus's critics think Earth was stationary? (Select all that apply.)

They didn't realize that stars could be very, very far away. They observed no parallax motion of the stars.

Identify the contributions made by the ancient astronomers of East Asia. (Select all that apply.)

They predicted the dates of eclipses. They kept detailed records of exploding stars. They noted dark sunspots.

Which of the following contributions to astronomy came from Islamic scholars?

They preserved and added to ancient Greek astronomical knowledge. They introduced the use of algebra. They gave (Arabic) names, still used today, to many stars.

True or false: Planets typically move from west to east against the backdrop of the stars.

True Yes, as planets move along their orbits, they slowly move west to east past the background of distant stars. (This doesn't mean they rise in the west. The stars, planets, and the whole celestial sphere rise in the east and set in the west daily because of Earth's rotation.)

Match the descriptions of Galileo's trial to either true or false.

True: Galileo was put on trial because he supported Copernicus's theory. Galileo was lucky to only receive house arrest as punishment.Galileo was lucky to only receive house arrest as punishment. False The pope was an enemy of Galileo. The Church admitted it was wrong the year after Galileo died.

A small circular motion carried along a planet's larger circular orbit around Earth was called an _____ in Ptolemy's model.

epicycle

An ellipse ____. (Select all that apply.)

has two foci has both long and short axes

A_____model places the Sun at the center of the Solar System, with the planets orbiting around it.

heliocentric

Angular size ____. (Select all that are correct.)

is a measure of how big an object looks can be measured in degrees

Copernicus's model is considered simpler than Ptolemy's because ____.

it can explain retrograde motion with just one circular orbit for each planet

If a comet orbits the Sun on a highly elongated elliptical orbit, then ____.

it will spend most of its time far away from the Sun

Select all the answers that correctly finish the sentence: According to the angular size formula, an object will have a small angular size if it is ____.

large and very, very far away small and far away

True diameter is ____. (Select all that apply.)

measured in units of length different than angular diameter but related to it

Eratosthenes's calculation made use of the fact that because the Sun is very far away from Earth, its rays of light are____ as they arrive at Earth.

parallel

The orbital______of a planet is how long it takes to complete one orbit around the Sun.

period

Renaissance scientists considered Copernicus's model more powerful than Ptolemy's because it ____. (Select all that apply.)

required fewer special conditions, such as the alignment of Venus's and Mercury's spheres in Ptolemy's model could be used to estimate the relative sizes of the orbits of planets

Simple geocentric models, such as the one by Eudoxus, explain the speed of a planet's movement across the sky but don't explain_____motion very well.

retrograde

Half of the long dimension of an ellipse (a in the figure) is called the ____.

semimajor axis

The figures are not to scale. If they were, then the Sun would be 400 times as far from Earth as the Moon. In this case in the right figure, the half-lit Moon and Sun would appear ____.

separated by almost 90° on the sky

Select all the answers that correctly finish the sentence: According to the angular size formula, an object will have a large angular size if it is ____.

small and very close large and close

In a simple geocentric model, which celestial objects were thought to be closer to Earth than the Sun was?

the Moon, Mercury and Venus

The ancient Greek astronomer Aristarchus measured the angle, α, of the right triangle shown in the image to determine...

the relative distances of the Sun and Moon.

Copernicus found that a heliocentric model did a better job than a geocentric model in explaining _____. (Select all that are correct.)

the retrograde motion of the planets the hundreds of years of new planetary observations since Ptolemy

The Moon illusion is caused by ____.

the way your brain subconsciously compares the size of the Moon to objects on the horizon

Which planet was discovered because of the effect its gravity had on the orbit of another planet?

Neptune Reason: Yes, Neptune's gravity caused Uranus to move in an unexpected manner.

Select all the statements that correctly describe Galileo's important astronomical discoveries.

Venus goes through phases like the Moon. Jupiter has moons. The Sun has sunspots.

Using the equation from Kepler's third law, calculate the period of a planet's orbit (p) if its average distance from the Sun (a) is 16 A.U.

64 years Reason: The first step is to cube the distance. p = a3

Select all the following situations that are similar to Copernicus's explanation for retrograde motion.

A runner on an inner track lapping a slower runner on an outer track. A fire truck overtaking and passing other vehicles on the road.

Match the ancient Greek astronomers with their famous work.

Aristarchus: estimated the size and distance of the Sun and Moon. Aristotle: argued that Earth was spherical in shape. Eratosthenes: calculated the size of Earth.

The ancient Greek astronomer_____argued Earth was shaped like a sphere based on observations of lunar eclipses?

Aristotle

The ancient Greek astronomer___argued Earth was shaped like a sphere based on observations of lunar eclipses?

Aristotle

Which of the following is a reason why Copernicus's theory was no better than Ptolemy's at predicting planetary positions.

Copernicus kept using circular orbits for the planets.

Ptolemy's model uses epicycles to explain ____.

a planet's retrograde motion

The apparent diameter or length an object extends across on the sky is called its _____ size.

angular

_____is an ancient belief system that holds that the positions and patterns of celestial objects influence events on Earth. _____is a system of knowledge that attempts to explain the nature of celestial objects using the scientific method.

Blank 1: Astrology Blank 2: Astronomy

The planet _____ was discovered because its_______force caused irregularities in the orbit of the planet______

Blank 1: Neptune Blank 2: gravitational or gravity Blank 3: Uranus

There were numerous models of the solar system. _____remained unconvinced of the validity of the _____model because he could not detect any stellar parallax. (Use one word to fill each blank.)

Blank 1: Tycho Blank 2: Copernican

To calculate the size of Earth using the angles of shadows, Eratosthenes needed to know that rays of sunlight are_____lines when they reach Earth and the_____between Alexandria and Syene.

Blank 1: parallel Blank 2: distance

How could you estimate the distance to the Sun like Aristarchus did?

By measuring the angles of a right triangle formed by the Sun, Earth, and the Moon.

Which of the following is Ptolemy known for today?

Creating a detailed geocentric model of the Solar System

If the angle between Alexandria, Earth's center, and Syene had been smaller than 7°, but the distance between the two cities was still 5,000 stadia, how would Eratosthenes's measurement have been different?

Earth's size would be bigger.

Under what circumstance would a planet not always appear close to the ecliptic?

If its orbit did not lie in the same plane as those of the other planets.

Select all the answers that correctly explain why photography was such an important discovery for astronomers.

It allowed astronomers to make permanent records of their observations. It allowed astronomers to see fainter objects than was possible before.

Select all the following statements that correctly describe Kepler's third law.

It tells us the relationship between a planet's orbital period and its semimajor axis. It is possible to calculate a planet's distance from the Sun if you know its orbital period.

Select all of the following objects that have an angular size of 1/2°.

The Moon The Sun

Copernicus's model could not predict planetary positions much more accurately than Ptolemy's model because Copernicus used____orbits in his model, something Kepler later corrected.

circular or circle

The parallax of a star would be smaller if the star were ____.

farther from Earth