CH 02 HW

A solar eclipse that occurs when the new moon is too far from Earth to completely cover the Sun can be either a partial solar eclipse or a(n) ___

annular eclipse

When is the next opportunity to see a total solar eclipse in the United States?

april 8, 2024

Watch the Causes of Lunar Phases video. To understand phases of the Moon, you must imagine the view from Earth looking out to the Moon as it orbits. At what position(s) in its orbit would we see all of the Moon's daylight side and none of its night side

at the point on the far left

Look again at the Causes of Lunar Phases video. At what position(s) in the Moon's orbit would we see exactly half of the Moon's daylight face and exactly half of its night face?

at the two points at the top and bottom

Eclipse seasons do not occur exactly twice a year. Instead, they occur slightly more often, coming about 173 days apart (which is a bit less than the roughly 182 to 183 days that make up 6 months). Why do they do this, rather than occurring exactly twice each year?

because the line of nodes gradually moves around the Moon's orbit

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

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

As seen from Earth, the Sun appears to follow the annual path that we call the __________ around the celestial sphere.

ecliptic

Based on their inability to detect stellar parallax, the ancient Greeks concluded that _________.

either Earth is the center of the universe or stars are extremely far away

Play the Moon Orbit video through to where you see the Moon orbiting Earth at correctly scaled sizes. Notice that Earth's daylight side (white) is on the right in this view, and its night side (gray) is on the left. Where along its orbit would the Moon also have its daylight side on the right and its night side on the left?

everywhere along its orbit

Consider the Moon when it is in the position shown in the moon phase diagram below. How much of the Moon's total surface is illuminated by sunlight at this time?

exactly half

Suppose you see a moon that is half bright and half dark in your early evening sky. Then you are seeing a __________ moon.

first quarter

the dark, central region of an object's shadow, in which light from the Sun is fully blocked

full shadow (umbra)

Start at the beginning of the Moon Orbit video, which shows the Sun and part of Earth's orbit. If we wanted to show the Moon's orbit on the scale of this starting frame, we would need to draw a circle that __________.

is smaller than one of the green dashes that show Earth's orbit

The moon will rise a little ___ each day, and with each passing day you will see a little ___ of the Moon's face illuminated.

later, more

Step 1 is to draw a diagram that shows the Moon in the correct position for the phase being considered. Which diagram below correctly shows the location of a third quarter moon?

moon is on top

Suppose you look up in the sky and the Moon appears as in the photo below. Which of the following diagrams correctly shows the Moon's location in its orbit around Earth for this phase?

moon to the right

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

new

A point at which the Moon crosses Earth's orbital plane is called a(n) ____

node

Again consider the position of the Moon shown in part A. How much of the Moon's surface is covered by Earth's shadow?

none

A first quarter moon rises at about ___, reaches its highest point in the sky at about ___, and sets around___

noon, sunset, midnight

Suppose you live at a mid-latitude in the Southern Hemisphere (such as in Australia, New Zealand, Chile, or South Africa). When will you have 12 hours of daylight and 12 hours of darkness?

on both the March and September equinoxes

the larger, surrounding region of an object's shadow in which light from the Sun is only partially blocked

partial shadow (penumbra)

During some lunar eclipses, the Moon's appearance changes only slightly, because it passes only through the part of Earth's shadow called the____

penumbra

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 final step is to determine the rise and set times for this phase. Which of the following are the correct times for a third quarter moon?

rise: about midight; set: about noon

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

About what time is it for the person who sees the third quarter moon at its highest point (position 4 in the diagram from Part B)?

sunrise

A new moon rises at about ___, reaches its highest point in the sky at about ___, and sets around___

sunrise, noon, sunset

A full moon rises at about ___, reaches its highest point in the sky at ___, and sets around___

sunset, midnight, sunrise

Which of the following accurately describe an eclipse season?

- During an eclipse season, there will be a lunar eclipse at full moon. - During an eclipse season, there will be a solar eclipse at new moon - An eclipse season occurs when the nodes of the Moon's orbit are lined up with Earth and the Sun

Which of the following statements are true about summer compared to winter?

- Temperatures tend to be warmer in summer. - You have more daylight and less darkness in summer. - The Sun follows a longer and higher path through your sky in summer.

Although the Causes of Lunar Phases video is very useful for learning about phases of the Moon, it is inaccurate in some ways. Which of the following correctly identify inaccuracies with this video?

- The Moon is too big compared to its orbit. - Earth is too big compared to the Moon's orbit. - The Moon is too big compared to Earth. - The astronaut is too big compared to the Moon.

Each of the following figures shows Earth with a different axis tilt. (Assume that Earth's rotation period is unchanged.) Each also shows a person located in Florida (not to scale). Rank the figures based on how much time the person spends in daylight during a 24-hour period, from most to least.

- Tilt = 23 1/2 (red circle to the right) - Tilt =0 - Tilt = 23 1/2 (red circle to the left) - Tilt =45

Which of the following statements about phases of the Moon are true? Select all that apply.

- if it is full moon, the Moon will rise around sunse - 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

What conditions must exist for a lunar eclipse to occur?

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

Observations of stellar parallax therefore provide direct evidence that:

- some stars are more distant than others - earth orbits the sun

What conditions must exist for a solar eclipse to occur?

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

The following figures are the same as those from Part A. This time, consider the seasonal differences that occur as Earth orbits the Sun with the different axis tilts. Rank the figures on the basis of the seasonal temperature differences you would expect between summer and winter, from the one with the most extreme seasonal differences to the one with the least extreme. To rank items as equivalent, overlap them.

- tilt = 90 - tilt = 45 tilt = 23 1/2 and 23 1/2 (on top of each other) - tilt = 0

Today, astronomers can detect and measure stellar parallax for thousands of the nearest stars, providing us with direct evidence that Earth really does orbit the Sun. Moreover, as the Parallax Angle animation shows (return to the main "Parallax" screen, and select the "Parallax and Distance" button), these measurements allow us to calculate distances to these relatively nearby stars. If we hope to use parallax to measure distances to even more-distant stars, which of the following telescopes would be most useful?

A telescope that orbits the Sun in the outer solar system

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.

The Sun rises and sets each day because

Earth rotates once each day

hat is the basic reason that we have seasons on Earth

Earth's axis is tilted relative to the ecliptic plane.

As you saw in Part C, stellar parallax exists only because Earth orbits the Sun. Therefore, if the ancient Greeks had measured stellar parallax, they would have known that their belief in an Earth-centered universe was wrong. Why didn't the ancient Greeks measure stellar parallax?

Even for the nearest stars, parallax angles are too small to measure with the naked eye.

As you saw in Part D, stellar parallax exists only because Earth orbits the Sun. Therefore, if the ancient Greeks had measured stellar parallax, they would have known that their belief in an Earth-centered universe was wrong. Why didn't the ancient Greeks measure stellar parallax?

Even for the nearest stars, parallax angles are too small to measure with the naked eye.

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.

The combination of the 173-day period between eclipse seaons and the Moon's approximately 29 1/2 - day cycle of phases leads to what we call the saros cycle, which lasts about 18 years, 11 1/3 days. Which of the following accurately describe something about the saros cycle?

If there is a solar eclipse in your home town today, there will be a solar eclipse in a different part of the world 18 years, 11 1/3 days from now

What happens to Earth's axis as we orbit around the Sun over the course of each year?

It remains pointed in the same direction at all times.

What is special about the June solstice?

It's the day on which the Northern Hemisphere receives its most direct sunlight.

Which of the following planets has essentially no seasons at all?

Jupiter (axis tilt = 3.1°)

Sort each item into the correct bin based on whether it describes lunar eclipses or solar eclipses.

Lunar: - occurs when Earth's shadow falls on the Moon - occurs when the Moon is on the direct opposite side of Earth from the Sun - can be seen by anyone on Earth's night side at the time - can occur only at full moon Solar: - occurs when the Moon comes directly between Earth and the Sun - can be seen only along a relatively narrow path on Earth - occurs when the Moon's shadow falls on Earth - can occur only at new moon

Based on what you have learned from your rankings in Parts A and B, which of the following planets would you expect to have seasons most like Earth's?

Mars (axis tilt = 25.2°)

Why will total solar eclipses no longer be possible after about 600 million years from now

The Moon will have moved too far from Earth for it to fully block the Sun

As you play the Moon Orbit video, notice how the arrows representing the Sun's rays are at first spread apart but become parallel as the video zooms in on the Moon's orbit. Why do the Sun's rays become parallel at the end of the video?

The Sun is so far away compared to the size of the Moon's orbit that all the rays reaching the orbit come from essentially the same direction.

Notice that the parallax is greater (the apparent movement is larger) for the person than for the trees, and that the mountains do not appear to shift at all. Why?

The amount of parallax depends on an object's distance, with greater parallax for nearer objects.

Consider again the portion of the video discussed in Part A. Notice that in the view through the camera, the parallax is larger (the apparent movement is larger) for the man than for the trees, and that the mountains do not appear to shift at all. Why?

The amount of parallax depends on an object's distance, with larger parallax for nearer objects.

Beginning about 55 seconds into the video, you'll see an animation of a photographer looking through her camera at a man, a set of trees, and distant mountains. Notice that, as viewed through the camera, the positions of the man and the trees change (relative to distant mountains) as the photographer moves. Which of the following statements correctly describes what is really happening in this situation?

The photographer is moving, but the man and the trees are staying still.

On the main screen of the interactive figure, select "Parallax", then select the "Introduction to Parallax" button. Click the play button to watch the animation, and watch how the motion of the photographer (lower window) affects what the camera sees (upper window). Which of the following statements correctly describes what is really happening? (Note: You need not continue with the next button to answer this question.)

The photographer is moving, but the person being photographed and the trees are staying still.

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.

Which of the following planets should have the most extreme seasons?

Uranus (axis tilt = 97.9°)

Look again at the Causes of Lunar Phases video. As the Moon orbits, notice how the astronaut's head always points toward Earth. What do we see from Earth that occurs for the same reason? (Be sure you are viewing the first portion of the video, with the rotating Moon, not the hypothetical, non-rotating view, shown afterward.)

We always see the same face of the Moon.

Just as you found for parallax on Earth, stellar parallax is larger for stars that are nearer and smaller for stars that ar more distant. Which statement best summarizes why stellar parallax occurs? You may find it helpful to watch the animation of stellar parallax that begins at about 1:20 into the video.

We view nearby stars from different positions in Earth's orbit at different times of year.

Stellar parallax occurs in much the same way as parallax on Earth, with greater parallax for stars that are nearer. Return to the main "Parallax" screen, and from here select the "Stellar Parallax" button, and watch how the motion of the star changes in the "View from Earth" window. Which statement best summarizes why stellar parallax occurs?

We view nearby stars from different positions in Earth's orbit at different times of year.

What is an annular eclipse?

a solar eclipse in which the Moon does not appear large enough to fully block the Sun

As discussed in the video, parallax measurements allow us to calculate distances to stars for which parallax is detectable. Suppose you have a telescope capable of measuring parallax shifts of a particular amount (for example, 0.001 arcsecond). Which of the following locations for the telescope would allow you to measure distances to the most distant stars?

a telescope on Mars

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

A waxing gibbous moon rises at about ____, reaches its highest point in the sky at about ___, and sets around ___

3pm, 9pm, 3am

Step 2 is to place a person in the position on Earth where the Moon would be overhead or at its highest point in the sky and determine the time for that person. At which of the four numbered positions shown below would the person be seeing the third quarter moon be at its highest point in the sky?

4

A waxing crescent moon rises at about ___, reaches its highest point in the sky at about ___, and sets around

9am, 9pm

A waning gibbous moon rises at about ___, reaches its highest point in the sky at about ___, and sets around ___

9pm, 3am, 9am

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.

A(n) ____ can occur only when the Moon is new and has an angular size larger than the Sun in the sky.

total solar eclipse

Anyone looking from the night side of Earth can, in principle, see a(n)___

total solar eclipse

Approximately how often do eclipse seasons occur?

twice a year

partial lunar eclipse begins when the Moon first touches Earth's___

umbra

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