Astronomy 101 Ch. 2

The planet _____________ was discovered because its______________force caused irregularities in the orbit of the planet___________________________ .

neptunegravitationaluranus

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

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

Aristotle

Which ancient Greek scientist was the first to use scientific observations to argue that Earth is round?

Aristotle

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

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

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

1. The Moon2. Mercury3. Venus4. The Sun5. Mars6. 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. Instructions

1. Tycho had an intense passion for studying astronomy2. Tycho designed & built the most accurate observational tools up to that date3. Tycho made the most precise measurements of planetary positions4. Tycho's meticulous observations were used to show the true shape of planetary orbits5. With the right orbital shape the heliocentric model accurately predicts planetary motions

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 system2. exploding stars are not part of the solar system3. jupiter has its own moons4. the law of gravity

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). Instructions

1. earth is the center of the solar system2. exploding stars are not part of the solar system3. jupiter has its own moons4. the law of gravity

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

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.

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.

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

Aristotle

____________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.

Astrology Astronomy

Match the scientific and technical advances with the discoveries they helped make. Instructions

Bigger telescopes - Nature of nebulaeStudy of heat - Power source of starsPhotography - Permanent records of observations

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 a reason why Copernicus's theory was no better than Ptolemy's at predicting planetary positions.

Copernicus kept using circular orbits for the planets. Reason: Planetary orbits are actually shaped like ellipses.

Which of the following is Ptolemy known for today?

Creating a detailed geocentric model of the Solar System

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

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

Match each piece of evidence for a spherical Earth on the left with the the way it was observed on the right.

Earth's shadow is curved. = Watch a lunar eclipse. Visible stars are different at different latitudes.= Travelers move south on Earth's surface. Tops of tall buildings remain visible even at great distances. = Move away from a city.

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

False Reason: Correct, angular diameter depends on both true diameter and distance. An object with a large angular diameter might be small but very close to the observer. For example, if you are wearing sunglasses, they might cover more than 100° of your view but are only a couple of inches wide.

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

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

Match the astronomers with their famous accomplishments.

Galileo - discovered the phases of Venus.Kepler - showed that planetary orbits are elliptical, not circularCopernicus - proposed a heliocentric model for the Solar System.Tycho Brahe - made the most accurate pretelescope measurements of planetary positions.

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.

Select all that correctly describe Ptolemy.

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

Why did the Catholic Church put Galileo on trial?

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

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

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. Reason: Yes, according to Kepler's third law, a planet with a shorter period will be closer.

Select all that correctly describe the Moon illusion.

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

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

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

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

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 Reason: Yes, in Ptolemy's model Mercury, like Venus, could never move behind the Sun from Earth's point of view. As such, it could never appear as more than a crescent, in contradiction to the full set of phases it actually displays.

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.

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

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

Match each model of the Solar System with its description. Instructions

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 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.

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

The Moon The Sun

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

The Moon The Sun

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

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 the Earth

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

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.

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

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

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.

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.

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

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

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

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

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

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

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: Ancient Chinese astronomers discovered sunspots.

True Reason: Chinese astronomers observed them much earlier than did Galileo, who was the first person to observe them with a telescope.

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

angular

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

angular

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

True Reason: 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.)

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.)

Tycho Copernican

Ptolemy's model uses epicycles to explain ____.

a planet's retrograde motion

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

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

epicycle

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

farther from Earth

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 or Copernican

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 Reason: Yes, remember Ptolemy's model had a large circular orbit and numerous smaller epicycles 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 Reason: Yes, many comets spend decades in the outer part of the Solar System and pass close to the Sun only for a few years.

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 ____.

large and close small and very close

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

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

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.

nothing the Sun

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

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.

parallel distance

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

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

The path of Mars on the sky shown in the image is known as ___________ motion.

retrograde

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

semimajor axis Reason: Yes, this is written as "a" in Kepler's third law.

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 small angular size if it is ____.

small and far away large and very, very far away

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

the Moon, Mercury and Venus

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

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

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

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.

The Moon illusion is caused by ____.

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

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.