Homework 3 Astronomy

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 midnight; set: about noon

Part complete 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

What is an annular eclipse?

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

When would a new Venus be highest in the sky?

at noon

Part complete Which of the following orbits has the largest semimajor axis?

fatter oval

suppose you see a 1st quarter moon in your evening sky. How will the Moon's appearance change in the next few days? 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

Which of the following orbits is the most eccentric?

more narrow oval

Approximately how often do eclipse seasons occur?

twice a year

Again consider the position of the Moon shown in part A. What does the Moon look like in our sky at this time?

waxing crescent

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?

waxing gibbous

Rank the pictured phases from left to right based on the order in which you would see them over the subsequent four weeks, from first seen to last.

waxing gibbous, 3rd, waxing crescent, waning gibbous, 1st

Which of the following paths could not be a real orbit for a planet around the Sun?

off centered oval

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.

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.

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?

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

Part complete 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?

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

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

Part complete Jupiter orbits the Sun at an average distance of 5.203 AU and takes 11.86years to complete each orbit. Based on these facts, which statement is true?

11.86^2=5.203^3

Part complete 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

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

1st quarter

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, 9 pm, 3 am

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

What is the circumference of Tirth?

7.2×10^4 km or 72,000

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

9am, 3pm, 9pm

A waning gibbous moon rises at about _______, reaches its highest point in the sky at about _____, and sets around ______.

9pm, 3am, 9am

Which of the following statements about scientific models is true?

A model can be used to explain and predict real phenomena.

Suppose the planet Uranus were much brighter in the sky, so that it was as easily visible to the naked eye as Jupiter or Saturn. Which one of the following statements would most likely be true in that case?

A week would have eight days instead of seven, despite the year length being unchanged.

Rank each of the six lunar positions based on the amount of the Moon's total surface that is illuminated by sunlight. If two (or more) diagrams have an equal amount of surface illuminated by sunlight, put one on top of the other. (Assume that conditions for an eclipse are not met in any of these diagrams.)

All piled into the same category, no order

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

April 8, 2024

Earth is slightly closer to the Sun in January than in July. How does the area swept out by Earth's orbit around the Sun during the 31 days of January compare to the area swept out during the 31 days of July?

Both areas are the same.

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.

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.

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

Full shadow (umbra)

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.

All of the following statements are true. Which one can be explained by Kepler's second law?

Mars moves faster in its orbit when it is closer to the Sun than when it is farther from the Sun.

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

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

Partial shadow (penumbra)

Kepler's second law states that as a planet orbits the Sun, it sweeps out equal areas in equal times. Which of the following statements describe a characteristic of the solar system that is explained by Kepler's second law?

Pluto moves faster when it is closer to the Sun than when it is farther from 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.

A full moon rises at about ______, reaches its highest point in the sky at ______ , and sets around _______.

Sunset, midnight, sunrise

Why are lunar eclipses more commonly seen than solar eclipses?

The Earth casts a bigger shadow than the Moon.

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.

Summarize the development of the Greek geocentric model through Ptolemy. How did the Ptolemaic model account for apparent retrograde motion?

The Ptolemiac model was able to explain retrograde motion by having the planets move on smaller circles attached to the larger circles on which they went around Earth.

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.

You discover an asteroid that orbits the Sun with the same 1-year orbital period as Earth. Which of the following statements must be true?

The asteroid's average (semimajor axis) distance from the Sun is 1AU.

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.

The video states that the planetary orbits are shown to scale. Which statement correctly describes the way the planet sizes are shown compared to their orbits?

The planets are all much too large compared to their orbits.

What do the structures of Stonehenge, the Templo Mayor, and the Sun Dagger all have in common?

They were all used by ancient peoples for astronomical observations.

All of the following statements are true. Which one can be explained by Kepler's third law?

Venus orbits the Sun at a faster orbital speed than Earth.

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.

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.

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.

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 arcosecond). Which of the following locations for the telescope would allow you to measure distances to the most distant stars?

a telescope on Mars

Part complete 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

Part complete 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

A first quarter moon rises at about _________, reaches its highest point in the sky at about _______, and sets around _______.

noon, sunset, 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

Part complete 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

Which of the following orbits shows the planet at aphelion?

fatter oval

If the Moon is setting at 6 A.M., the phase of the Moon must be

full

Which photo shows what the Moon looks like when it is in the position shown in the following moon phase diagram?

full moon

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

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.)

full, waning gibbous, the quarters, waxing crescent, new

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

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

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

Which diagram below correctly shows the location of a third quarter moon?

moon directly above earth

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

never

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