AST 101 Chapter 2: The Rise Of Astronomy
The apparent diameter or length an object extends across on the sky is called its __________ size.
Angular (Measured in degrees)
Which ancient Greek scientist was the first to use scientific observations to argue that the Earth is round?
Aristotle
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 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 (Yes, small objects can appear big only if they are very close.)
True diameter _____. (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
Select all of the following that were important astronomical contributions made by Tycho Brahe.
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 Making very accurate measurements of planet positions (Yes, his positions measurements were the best up to that time.)
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
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
To calculate the size of Earth using the angels 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
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. P2=A3 Planets move in elliptical orbits with the Sun at one focus.
Select all the apparent planetary motions that are not a result of Earth's rotation.
Planets occasionally move backwards across the sky. Planets move west to east with respect to the stars. Planets always stay very close to the ecliptic.
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. (Yes, importantly, Copernicus was able to use his model for more than just explaining the observations that motivated it.)
Planets normally move from the west to the east with respect to the stars. Occasionally, they move east to west for a weeks, which is called _________ motion.
Retrograde
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
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 path of Mars on the sky shown in the image is known as __________ motion.
Retrograde
Copernicus found that a heliocentric model did a better job than geocentric model in explaining ________. (Select all that are correct.)
Retrograde motion The Hundreds of years of new planetary observations since Ptolemy.
Ptolemy's model uses ecicycles to explain _________.
A planet's retrograde motion
Angular size ________. (Select all that are correct.)
Can be measured in degrees Is a measure of how big an object looks (Yes, Objects can appear big either because they really are big or because they are very close.)
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
If the angel 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 Eratosthene's measurement have been different?
Earth's size would be bigger.
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 (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.
The planet _____ was discovered because its _____ force caused irregularities in the orbit of the planet ______.
Neptune Gravitational Uranus
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. (Parallel rays of light make it possible to calculate the angel between Alexandria, Earth's center, and Syene.)
The ancient Greek astronomer Aristarchus measured the angel, A, of the right triangle shown the image to determine
The relative distances of the Sun and Moon. (Using trigonometry, he estimated the Sun to be 20 times farther away from Earth than the Moon (it's really closer to 400, but it's a very difficult measurement to make, even today.)
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" durign retrograde motion would be bigger and last longer for a larger epicycle. (Yes, with a larger epicycle, the planet would movee backward for a larger distance.)
Under what circumstances would you measure a large parallax for a star?
The star is very close to Earth. (Smaller distances cause larger parallaxes.)
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 circle called epicycles. (Yes, epicycles are how the Greeks accounted for retrograde motion.) The planets, the Sun, the Moon move around Earth
The Moon illusion is caused by ________.
The way your brain subconsciously compares the size of the Moon to objects on the horizon.
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 didn't understand that stars could be so far away, making their parallax undetectable.) They observed no parallax motion of the stars.
Select all the contributions to astronomy from Islamic scholars
They gave (Arabic) names, still used today, to many stars. They introduced the use of algebra. They preserved and added to ancient Greek astronomical knowledge.
If the Moon was three times farther away from us than it now is, its angular size would be.
Three times smaller
True or False: Ancient Chinese Astronomers discovered sunspots
True (Chinese astronomers observed them much earlier than did Galileo, who was the first person to observe them with a telescope)
Which ancient Greek scientist was the first to scientific observations to argue that the Earth is round?
Aristotle (Aristotle argued that the Earth was round because its shadow on the Moon during a lunar eclipse is round.)
________ 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
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
According to Kepler's second law, planets move ______ in their orbits when closer to the Sun and _________ when they are farther away.
Fastest Slowest
An ellipse _______. (Select all that apply.)
Has both long and short axes. Has two foci
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. (Yes, Before Gablileo, it was thought that the Sun was a perfect celestial orb.)
A _____ model places the Sun at the center of the Solar System, with the planets orbiting around it.
Heliocentric
A ___________ model places the Sun at the center of the Solar System, with the planets orbiting around it.
Heliocentric
Copernicus's model is considered simpler than Ptolemy's because _________.
It can explain retrograde motion with just one circular orbit for each planet (Yes, remember ptolemy's model had a large circular orbit and numerous small epicycles for each planet.)
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. (Yes, according to Kepler's third law, a planet with a shorter period will be closer.)
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. (Yes, many comets spend decades in the outer part of the Solar System and pass close to the Sun only for a few years.)
To calculate the true diameter of a planet, what information do you need (Select all that apply.)
Its Distance Its Angular Diameter
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. (Yes, Ockham's razor says model should be as simple as possible, not that that they can never be complex.)
Half of the long dimension of an ellipse (a in the figure is called the ______.)
Semimajor Axis
Half of the long dimension of an ellipse (a in the figure) is called the ________.
Semimajor Axis (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 (Yes, Aristarchus argued that the Sun was much farther away than the Moon based on this argument.)
Select all the statements that correctly describe Galileo's important astronomical discoveries.
The Jupiter has moons The Sun has sunspots Venus goes through phases like the moon (Yes, Venus's phases proved that Venus moved around the Sun.)
Select all of the following objects that have an angular size of 1/2
The Sun The Moon
Select all of the objects for which Aristarchus estimated the size, relative to Earth.
The Sun The Moon
Select all of the objects for which Aristarchus estimated the distance.
The Sun (Yes, he calculated the Sun's distance as 20 times the Moon's distance *It's closer to 400 times, but it's a very difficult measurement.) The Moon (Yes, he calculated the Moon's distance as 70 times Earth's radius *it's closer to 60*)
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 angel would be smaller.
How would the angel between Alexandria, Earth's center, and Sydene change if the distance between them were 1000 stadia instead of 5000 stadia?
The angle would be smaller.
Select the properties of Eudoxus's (an ancient Greek) geocentric model of the solar system.
The planets move around Earth. The Sun and Moon move around Earth. Objects closest to Earth move fastest.
