HW #1 - Discovering The Universe (Chapters 1 & 2)
Due: 11:59pm on Sunday, September 16, 2012
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Problem 1.25
Choose the best answer.
Part A
Which of the following correctly lists our "cosmic address" from small to large?
ANSWER:
Problem 1.26
Choose the best answer.
Part A
When we say the universe is expanding, we mean that:
Problem 1.27
Choose the best answer.
Part A
If stars existed but galaxies did not:
ANSWER:
Problem 1.28
Choose the best answer.
Part A
Could we see a galaxy that is 20 billion light-years away?
Problem 1.30
Choose the best answer.
Part A
If we represent the solar system on a scale that allows us to walk from the Sun to Pluto in a few minutes, then:
ANSWER:
Problem 1.31
Choose the best answer.
Part A
The total number of stars in the observable universe is roughly equivalent to:
Problem 2.27
Choose the best answer.
Part A
Two stars that are in the same constellation:
Problem 2.29
Choose the best answer.
Part A
Beijing and Philadelphia have about the same latitude but very different longitudes. Therefore, tonight's night sky in these two places:
ANSWER:
Key Concept: Lunar Phases I
Learning Goal:
To understand the scale of the Moon's orbit and how it leads to our seeing phases of the Moon.
Introduction: Parts A through C are based on the Moon Orbit animation. Open the animation and push the Play button to zoom in from a view of the inner solar system to a view of the Moon's orbit around Earth.
Launch the Causes of Lunar Phases animation Launch the Moon Orbit animation
Part A
Start at the beginning of the Moon Orbit animation, 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 __________.
As you play the Moon Orbit animation, notice how the arrows representing the Sun's rays are at first spread apart, but become parallel as the animation zooms in to the Moon's orbit. Why do the Sun's rays become parallel at the end of the animation?
Play the Moon Orbit animation through to the end, 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?
Now study the Cause of Lunar Phases animation, which shows the Moon orbiting around the rotating Earth. For this tutorial, you will need only the initial view in which the astronaut's head always points toward Earth. (Clicking "View Non-Rotating Moon" brings up a hypothetical view that shows what would happen if the Moon did not rotate at all.) This animation is not to scale.
Part D
Although this Cause of Lunar Phases animation 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 animation?
Look again at the Cause of Lunar Phases animation. To understand phases of the Moon, you must imagine the view from Earth (in the center of the animation) 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?
Look again at the Cause of Lunar Phases animation. At what position(s) in its orbit would we see exactly half of the Moon's daylight face and exactly half of its night face?
Look again at the Cause of Lunar Phases animation. 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 animation with the rotating Moon, not the hypothetical, non-rotating view.)
Ranking Task: Lunar Phases II
Part A
The following figures show a top view of Earth, sunlight, and six different positions of the Moon as it orbits Earth. Note that the distances shown are not drawn to scale. Rank each of the six lunar positions from left to right based on the amount of the Moon’s illuminated surface that is visible from Earth, from greatest to least. (If two diagrams have an equal amount of illumination as seen from Earth, put one on top of the other.)
Hint 1. A strategy that will help you find the answer
This ranking task requires you to know that the Moon’s phase depends on its position in its orbit. There are two key facts to remember as you study the diagrams showing the Moon at different positions in its orbit: 1. No matter where the Moon is located in its orbit of Earth, the half that faces the incoming sunlight is illuminated and e other half is dark. That is why all six diagrams show the right side of the Moon (facing the
Part B
Shown following are five different phases of the Moon as seen by an observer in the Northern Hemisphere. Imagine that tonight the Moon is in the waxing gibbous phase (as shown at the far left (labeled “first”) in the following ranking box). Rank the pictured phases from left to right based on the order in which you would see them over the next four weeks, from first seen to last.
Hint 1. A strategy that will help you find the answer
The Moon’s complete cycle of phases takes about 29 1/2 days (think “moonth” for month), so this task requires that you know the order in which we see the different phases in our sky. The following two key facts should help you determine the correct order: 1. Starting from new moon, when the Moon is in nearly the same place in the sky as the Sun, the phase gradually waxes until the Moon is full (about 2 weeks after new moon), then wanes until the Moon is new again (about 4 weeks after the prior new moon). 2. Remember that the phases proceed through an orderly progression; for example, we can’t suddenly see the illumination jump from the left side of the Moon to the right. With these two ideas in mind, start by asking yourself what phase we see next after the waxing gibbous moon (shown at the far left of the ranking box). Then work your way through the remaining phases to put the given photos in the correct order.
Hint 2. What do we see a few days after a waxing gibbous moon?
We see about 3/4 of the Moon’s face illuminated at waxing gibbous phase. What do we see about three to four days later?
ANSWER:
a crescent moon a “half moon” (in which the Moon in our sky is half dark and half light) a full moon
Correct
“Waxing” means on the way to being full, so you are correct that we’ll see a full moon just a few days after the waxing gibbous moon. Now, notice that a full moon is not offered among the photo choices, and ask yourself: What phase would we see next after full moon? With your answer, you should be able to find the correct item to rank first, and then a similar thought process will allow you to complete the rest of the task.
Hint 3. What do we mean by waxing and waning phases?
Which of the following correctly describes what we mean by “waxing” and “waning” phases of the Moon?
ANSWER:
Waxing means we see less than half the moon illuminated, and waning means we see more than half.
Waxing means phases that we see as the moon approaches full moon, and waning means phases that we see after full moon.
Waxing means we phases in which we can see large craters on the Moon, and waning means phases in which we can’t.
Correct
Waxing means on the way to being full and waning means the phases we see as the full moon wanes (or fades) away. Because the task asks you to start from a waxing gibbous phase, you now should realize that the Moon is on its way to being full at that time. Because a full moon is not offered among the photo choices, ask yourself: Once the Moon reaches its full phase, what will we see next? With your answer, you should be able to find the correct item to rank first, and then a similar thought process will allow you to complete the rest of the task.
Hint 4. The time required for the Moon to complete one cycle of phases
It takes the Moon approximately one month (29.5 days; think “moonth”) to complete one cycle of phases. herefore, when the task asks you to think about what you see over the next 4 weeks, it is really asking you to place the photos in the correct order for which they appear over one complete lunar cycle, starting from the waxing gibbous phase shown at the far left of the ranking box.
Seasons 1: What Is the Cause of the Seasons?
Learning Goal:
To understand the basic cause of the seasons and address a common misconception by showing that seasons are not related to Earth's varying distance from the Sun.
Introduction. Earth’s orbit around the Sun is elliptical (rather than circular), which means the Earth–Sun distance varies over the course of each year. The following table gives the Earth–Sun distance at the equinoxes and solstices:
Time of Year Earth–Sun Distance
March (northern spring) equinox 149.0 million km
June (northern summer) solstice 152.0 million km
September (northern fall) equinox 150.2 million km
December (northern winter) solstice 147.2 million km
Part A
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.
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.
Hint 1. Starting points of seasons in the Southern Hemisphere
Seasons in the Southern Hemisphere are opposite those in the Northern Hemisphere. Thus, winter in the Southern Hemisphere begins when
Earth is at the point in its orbit called the June (or northern summer) solstice, which occurs around June 21 each year. Similarly, Southern Hemisphere spring begins at the September (or northern fall) equinox around September 21, summer begins at the December (or northern winter) solstice around December 21, and fall begins at the March (or northern spring) equinox around March 21.
ANSWER:
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?
You’ve now seen that Earth’s varying distance cannot be the cause of our seasons. So what is the cause of the seasons?
Seasons 2: Why Is Summer Hotter than Winter?
Learning Goal:
To understand why summer days are longer and generally warmer than winter days.
Introduction. In this tutorial you will consider how the Sun's path through the sky differs in summer and winter. You will find it easier to interpret the diagrams in Parts A and B if you keep the following points in mind:
• Earth is always rotating, even though you cannot see this rotation because the diagrams are not animated.
• Sunlight sometimes comes from the left and sometimes from the right in the diagrams. This is because Earth maintains the same tilt (toward the left)throughout the year, so on one side of Earth's orbit the Sun will be to the left and on the other side it will be to the right.
• Based on the tilt and the direction of sunlight, you should be able to determine whether the person shown is in summer or in winter.
Part A
Each of the following figures shows a person (not to scale) located on Earth at either 40°N or 40°S latitude. Rank the figures based on how much time the person spends in daylight during each 24-hour period, from most to least. To rank items as equivalent, overlap them.
Hint 3. How long does it take each location to complete a full rotation?
Rank the figures on the basis of how much time it takes the person to complete one full rotation (around Earth's axis) at each location shown.
The following figures are the same as those from Part A. This time, imagine that each person places an identical glass of water outside. Consider only the effects of the season — meaning the amount of daylight and the height of the Sun's path through the sky — on the water temperature. Rank the figures based on the highest (warmest) temperature the glass of water would reach during a 24-hour period, from highest to lowest. To rank items as equivalent, overlap them.
Based on what you have learned from your rankings in Parts A and B, why is it generally hotter in summer than in winter?
Check all that apply.
Seasons 3: What if Earth’s Axis Tilt Were Different?
Learning Goal:
To understand how seasons would be affected by a greater or smaller axis tilt.
Introduction. What would happen to our seasons if Earth’s axis tilt were different from its actual 23.5°? This activity will help you answer this question and will also help you understand seasons on planets that have axis tilts different from Earth’s. As you examine the diagrams in parts A and B, keep in mind that Earth is always rotating, even though the diagrams do not show this rotation because they are not animated.
Part A
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.
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.
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?
Visual Activity: Conditions for Eclipses
First, launch the animation below. Explore the interactive animation before answering the questions. Be sure to notice that you can watch the animation in two modes: (1) with the Moon’s actual, tilted orbit; (2) or with the Moon in the “flat” orbit it would have if it orbited Earth in the same plane that Earth orbits the Sun (the ecliptic plane). The windows at the bottom show top and side views zooming in on the Moon’s orbit as the animation progresses. Also notice that in the “tilted” mode, the Moon’s orbit is colored white on the half that is above Earth’s orbital plane and blue on the half that is below this plane. Note that the animation emphasizes the relative positions of the Moon, Earth, and Sun but does not depict all types of eclipses that can happen in any single eclipse season; that is, it does NOT show all the eclipses that would occur in each situation, so be sure you focus on the concept rather than on trying to count the number of eclipses that you see.
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. (Click “Show Moon with flat orbit” to see this situation.) In this hypothetical situation, approximately how many solar eclipses would occur each year?
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 _____.
If you could change the layout of the solar system, which of the following would cause a lunar eclipse to occur at least once every month in this hypothetical situation?
Score Summary:
Your score on this assignment is 86.4%.
You received 34.57 out of a possible total of 40 points. [Show Less]