Homework assignment #2

Suppose you use the Southern Cross to determine that the south celestial pole appears 40 degrees above your horizon. Then you must be located at _________.

latitude 40 degrees south

An angle of 1 arcsecond is _________.

less than the thickness of a human hair held at arm's length

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

never

When would a new Venus be highest in the sky?

noon

Galileo challenged the idea that objects in the heavens were perfect by ________.

observing sunspots on the Sun and mountains on the Moon

The shadow cast by a simple stick or obelisk allowed ancient people to

tell the time of day

The Sun's path, as viewed from the equator, is highest in the sky on _________.

the March and September equinoxes

If our year were twice as long (that is, if Earth took twice as many days to complete each orbit around the Sun), but Earth's rotation period and axis tilt were unchanged, then _________.

the four seasons would each be twice as long as they are now

Which of the following statements about Kepler's laws is false?

Kepler's laws explain why planets with larger semi-major axes have much longer orbital periods.

Which of the following statements about constellations is false?

Most constellations will be unrecognizable hundreds of years from now

A total solar eclipse can only happen during what lunar phase?

NEW

Suppose it is full moon. What phase of Earth would someone on the Moon see at this time?

New Earth

The Sun-centered system pictured in the lower window of the video offers a simple explanation for observations of apparent retrograde motion. Should these facts alone have been enough to convince the ancient Greeks that Earth really does go around the Sun?

No, because the Greeks had an Earth-centered model that also accounted for apparent retrograde motion.

Kepler's third law states that a planet's orbital period, p, is related to its average (semimajor axis) orbital distance, a, according to the mathematical relationship p2=a3. Which of the following statements describe a characteristic of the solar system that is explained by Kepler's third law?

Venus orbits the Sun faster than Earth orbits the Sun. Inner planets orbit the Sun at higher speed than outer planets.

Refer to the data in the introduction. Rank the seasons for the Northern Hemisphere based on Earth's distance from the Sun when each season begins, from closest to farthest.

WINTER, SPRING, FALL, SUMMER

The Andromeda Galaxy is faintly visible to the naked eye in the constellation Andromeda. Suppose instead it were located in the same direction in space as the center of the Milky Way Galaxy (but still at its current distance). How would it appear to the eye in that case?

We could not see it at all.

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.

Which of the following statements about phases of the Moon are true? -at new moon, the half of the Moon facing the Sun is fully illuminated -the time between first-quarter moon and third-quarter moon is about a month -if it's new moon, the Moon will rise in the middle of the day -at new moon, the Moon's entire surface is engulfed in darkness -the time between new moon and full moon is about two weeks -if it is full moon, the Moon will rise around sunset -at new moon, we see only the "night" side of the Moon

-at new moon, the half of the Moon facing the Sun is fully illuminated -the time between new moon and full moon is about two weeks -if it is full moon, the Moon will rise around sunset -at new moon, we see only the "night side of the Moon

Which of the following conditions must exist for a solar eclipse to occur?

-moon phase is new, and Moon is passing through Earth's orbital plane

What conditions must exist for a solar eclipse to occur?

-must be a new moon -the Moon must be passing through Earth's orbital plane

What conditions must exist for a lunar eclipse to occur?

-must be full moon -Moon must be passing through Earth's orbital plane

Suppose that instead of being inclined to Earth's orbit around the Sun, the Moon's orbit was in the same plane as Earth's orbit around the Sun. In this hypothetical situation, approximately how many solar eclipses would occur each year?

12

In reality, the Moon's orbit about Earth is tilted (by about 5°) with respect to Earth's orbit about the Sun. As a result, the actual number of solar eclipses that occur each year is approximately _____.

2

Kepler's first law states that the orbit of each planet is an ellipse with the Sun at one focus. Which of the following statements describe a characteristic of the solar system that is explained by Kepler's first law?

>Earth is slightly closer to the Sun on one side of its orbit than on the other side. >The Sun is located slightly off-center from the middle of each planet's orbit.

Which of the following are the three key hallmarks of science?

>Modern science seeks explanations for observed phenomena that rely solely on natural causes. >Models must make testable predictions that will force us to revise or abandon the model if they do not agree with observations. >Science progresses through the creation and testing of models of nature that explain the observations as simply as possible

You observe a full moon rising at sunset. What will you see at midnight?

A full moon high in the sky

If the Moon is 3rd quarter phase, what shape does it have in the sky?

A half circle

According to Kepler's third law (p2 = a3), how does a planet's mass affect its orbit around the Sun?

A planet's mass has no effect on its orbit around the Sun.

When Copernicus first created his Sun-centered model of the universe, it did not lead to substantially better predictions of planetary positions than the Ptolemaic model. Why not?

Copernicus used perfect circles for the orbits of the planets.

At most times, Mars appears to move_____________ relative to the stars. The exceptions are during its periods of apparent retrograde motion, when Mars appears to move ________________ relative to the stars.

EASTWARD;WESTWARD

During the period each year when we see Mars undergoing apparent retrograde motion in our sky, what is really going on in space?

Earth is catching up with and passing by Mars in their respective orbits.

What is really happening in space during the periods when we see Mars going through apparent retrograde motion?

Earth is passing by Mars in its orbit around the Sun.

Part complete For most of history, the lack of observable stellar parallax was interpreted to mean that _________

Earth is stationary at the center of the universe

Which of the following best summarizes the reason we see phases of the Moon?

Half the Moon is always illuminated by the Sun, but the phase we see depends on how much of this half we are looking at from Earth.

How does Earth's varying distance from the Sun affect our seasons?

It doesn't. Earth's orbital distance plays no significant role in the seasons.

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

Perihelion

Refer to the data in the introduction. Rank the seasons for the Southern Hemisphere based on Earth's distance from the Sun when each season begins, from closest to farthest.

SUMMER, FALL, SPRING, WINTER

Suppose Earth's axis tilt was significantly greater than its current 23.5 degrees, but Earth's rotation period and orbital period were unchanged. Which statement below would not be true?

The length of each season (for example, the number of days from the summer solstice to the fall equinox) would be significantly longer than it is now.

All the following statements are true. Which one explains the reason that there is not a solar eclipse at every new moon? View Available Hint(s) All the following statements are true. Which one explains the reason that there is not a solar eclipse at every new moon? The Moon goes through a complete cycle of phases about every 29.5 days. The nodes of the moon's orbit precess with an 18-year period. The Moon is only about 1/4 as large as Earth in diameter. The orbital plane of the Moon is tilted slightly (by about 5 degrees) to the ecliptic plane.

The orbital plane of the Moon is tilted slightly (by about 5 degrees) to the ecliptic plane.

In the Greek geocentric model, the retrograde motion of a planet occurs when:

The planet actually goes backwards in its orbit around Earth

What happens during the apparent retrograde motion of a planet?

The planet appears to turn around in its eastward path through the stars and backs up for many nights traveling westwardly.

Which of the following best describes why we have seasons on Earth?

The tilt of Earth's axis causes different portions of the Earth to receive more direct sunlight and more hours of sunlight at different times of year.

You've now seen that Earth's varying distance cannot be the cause of our seasons. So what is the cause of the seasons?

The tilt of Earth's axis causes different portions of the Earth to receive more or less direct sunlight at different times of year.

Based on what you have learned from your rankings in Parts A and B, which statement best describes how variation in the Earth-Sun distance affects the seasons?

The variation in Earth-Sun distance over the course of each year has virtually no effect on the seasons.

Suppose you are facing north and you see the Big Dipper close to your northern horizon, with Polaris (and the Little Dipper) above it. Where will you see the Big Dipper in six hours?

To the right of Polaris; that is, 90 degrees counterclockwise from its current position

It's 6 am and the Moon is at its highest point in your sky (crossing the meridian). What is the Moon's phase?

Third quarter

Suppose you live in the United States and you see a crescent moon in your evening sky tonight. What will a friend in South America see tonight?

Your friend will also see a crescent moon.

We cannot see a new moon in our sky because _________.

a new moon is quite near the Sun in the sky

Part complete Kepler's second law, which states that as a planet moves around its orbit it sweeps out equal areas in equal times, means that

a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun.

Suppose you see a photo showing Jupiter half in sunlight and half in shadow (that is, a first-quarter Jupiter). This photo might have been taken by _________.

a spacecraft orbiting Jupiter

What is a circumpolar star?

a star that always remains above your horizon

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

aphelion

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?

at noon

Consider a time when Mars is in the middle of one of its periods of apparent retrograde motion. During this time, Mars appears _____ in our night sky and crosses the meridian around _____.

brightest; midnight

Which of the following statements about the celestial sphere is not true? a) The Earth is placed at the center of the celestial sphere. b) When we look in the sky, the stars all appear to be located on the celestial sphere. c) The "celestial sphere" is another name for our universe. d) The celestial sphere does not exist physically.

c) The "celestial sphere" is another name for our universe.

6. The extent to which Mars' orbit differs from a perfect circle is called its _______________.

eccentricity

3. Earth orbits in the shape of a/an ___________ around the Sun.

ellipse

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

focus

During a lunar eclipse the Moon's phase must be

full

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

When traveling north from the United States into Canada, you'll see the North Star (Polaris) getting _________.

higher in the sky

Why wasn't the Sun-centered model of Copernicus immediately adopted after he proposed it?

it was not noticeably more accurate than the old Ptolemaic model

In any particular place on Earth, certain constellations are visible in the evening only at certain times of the year because _________.

our evening view of space depends on where Earth is located in its orbit around the Sun

If you wanted to document the apparent retrograde motion of Mars, you would need to measure and record Mars's __________ over a period of __________.

position among the constellations; several months

The sun

seems to move around the celestial sphere daily to the East

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

semimajor axis

An original observation of Galileo's that helped to overturn the ancient Earth-centered model was

the phases of Venus

The point directly over your head is called _________.

the zenith