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Astronomy Assignments and Quizzes > Exam 1 Homework Questions > Flashcards

Exam 1 Homework Questions Flashcards

1
Q

The way scientists know that a hypothesis in astronomy is a reasonable description of nature is to…

A

do experiments and observations about the predictions of the hypothesis. 

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2
Q

A star is 230 light-years away. The light we see tonight from that star left it…

A

230 years ago. 

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3
Q

The location of the Earth in the Milky Way Galaxy is how far from the center?

A

a little less than 30,000 LY from the center. 

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4
Q

Even with the best and largest telescopes, we can’t see all the stars in the Milky Way Galaxy despite the fact that these same telescopes can show us other galaxies. This is because…

A

Dust in the space between stars builds up over large distances and blocks the light of stars behind the dustier parts of the Milky Way. 

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5
Q

The laws of nature (as determined by scientists) are constructed from…

A

many observations, hypotheses, and experiments. 

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6
Q

The Astronomical Unit (AU) as defined by astronomers is…

A

the average distance between the Earth and the Sun. 

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7
Q

What celestial object (excluding asteroids) is nearest to the Earth?

A

The Moon.

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8
Q

Written in correct scientific notation, the number 13.8 billion becomes

A

1.38 x 10^(10)

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9
Q

Suppose you started with 1.5 x 10^(2) and added 1.5 x 10^(4). How does the sum compare to the initial value?

A

The sum is much larger.

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10
Q

To determine the distance an object travels over a certain amount of time while moving at a constant speed, you should

A

multiply its speed by the time it took to travel.

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11
Q

If you increase a value by an “order of magnitude”, you have increased that value by a factor of…

A

10

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12
Q

In its early years, a relatively new vehicle company (whose chief executive is a great advocate for space exploration) lost 1.9 billion dollars on its operations. During that year, they delivered 258000 vehicles.
Calculate how much money was lost per vehicle sold.

A

Loss per car = 7364
dollars

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13
Q

The fastest human spaceship leaving the solar system is Voyager 1, which is traveling at 61,146 kilometers per hour. Imagine it is traveling to a star system 6.1 light-years away.
Calculate how long, in years, it will take for Voyager 1 to arrive.

A

1.077×10^(5) years

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14
Q

On January 2022, the New Horizons spacecraft reached a distance of 53 astronomical units (AUs) from the Earth.
If there are 150 million km in one AU, calculate how long it takes for New Horizons to send a radio wave signal back to Earth. (The speed of light is 300,000 km/s.) Express your answer in hours.

A

7.361hr

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15
Q

Rank the astronomical objects in terms of diameter, from smallest to largest.
Sun, Jupiter, Moon, Galaxy

A

Moon, Jupiter, Sun Galaxy

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16
Q

Because cosmic distances are so vast, astronomers use light-years as their unit of distance. One light-year is defined as __________. The nearest star is a little more than __________ light-years away from us. When we see light from a galaxy 2 million light-years away, it has taken __________ to reach us. Light from the Sun takes __________ to reach us.

A

Here’s the completion of your statements:

  1. One light-year is defined as the distance that light travels in one year, which is approximately 5.88 trillion miles (9.46 trillion kilometers).
  2. The nearest star is a little more than 4 light-years away from us (specifically, Proxima Centauri).
  3. When we see light from a galaxy 2 million light-years away, it has taken 2 million years to reach us.
  4. Light from the Sun takes about 8 minutes and 20 seconds to reach us.
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17
Q

Rank the Sun, Pleiades star cluster, Coma Cluster of Galaxies, the Moon and the Andromeda Galaxy by their distance from Earth, from nearest to farthest.

A

Moon, Sun, Pleiades star cluster, Andromeda Galaxy, Coma Cluster of Galaxies

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18
Q

True or False: An astronomical hypothesis is a piece of knowledge that every astronomer accepts.

A

False

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19
Q

True or False: Scientific models are always an approximation of nature.

A

True

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20
Q

True or False: The laws that scientists have found about how things work on Earth do not apply to the stars and other objects that astronomers study; those astronomical objects work by completely different rules.

A

FALSE

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21
Q

True or False: Light takes a little bit more than 8 minutes to travel the distance between the Earth the Sun.

A

True

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22
Q

True or False: Our Sun is not located in the center of the Milky Way Galaxy.

A

True

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23
Q

True or False: By looking billions of light-years out into space, astronomers are actually seeing billions of years into the past.

A

True

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24
Q

True or False: After studying the stars, astronomers have concluded that the most abundant element in the universe is oxygen.

A

False

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25
Q

The point in the sky directly above your head at any given time is called the…

A

zenith. 

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26
Q

From a city in the U.S., where in the sky would you look to see a star that is not turning with the motion of the sky in the course of a night?

A

At the north celestial pole 

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27
Q

The south celestial pole and the north celestial pole lie in the sky directly above

A

the Earth’s axis. 

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28
Q

Someone who observes the sky every clear night in Boston for many years will NEVER get to see:

A) The north circumpolar zone
B) The south circumpolar zone
C) The Orion constellation
D) The Milky Way galaxy

A

The south circumpolar zone. 

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29
Q

Where on Earth do stars always circle the zenith (and never rise and set)?

A

At the north pole

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30
Q

The strip of the sky through which the Sun, the Moon, and the bright planets appear to move in the course of a year is called…

A

the zodiac

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31
Q

Which of the following is NOT an argument for showing that the Earth must be round?

A) Ships disappearing hull-first over the horizon
B) The Earth’s shadow on the Moon during a lunar eclipse
C) The Sun is seen blocking different constellations in the course of a year
D) The varying positions of the North Star from different latitudes

A

The Sun is seen blocking different constellations in the course of a year. 

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32
Q

Which of the following was NOT done by Hipparchus, the great ancient astronomer?

A) Creating a star catalog with over 850 stars
B) Developing a method for predicting lunar eclipses
C) Explaining retrograde motion
D) Measuring the length of the year

A

Explaining retrograde motion 

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33
Q

How did Eratosthenes measure the size of the Earth?

A

By measuring the height of the Sun in the sky on the same day in two cities at different latitudes. 

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34
Q

The slow tipping of the Earth’s axis in a circle with a period of about 26,000 years is called

A

precession.

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35
Q

The great astronomer of ancient times who summarized and improved a system of circles upon circles to explain the complicated motions of the planets (and published the system in a book now called The Almagest) was

A

Ptolemy.

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36
Q

In Ptolemy’s system, the planets orbit the Earth and not the Sun. How did the system explain the retrograde motion of planets like Jupiter?

A

The planets moved on a small circle whose center, in turn, circled a point near the Earth.

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37
Q

Which of the following was NOT done by Galileo Galilei?

A) Improving the telescope and making astronomical observations
B) Discovering the four largest moons of Jupiter
C) Explaining retrograde motion with the heliocentric hypothesis
D) Observing the phases of Venus

A

Explaining retrograde motion with the heliocentric hypothesis. 

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38
Q

The Renaissance astronomer who wrote the pioneering book that suggested the Earth probably orbits the Sun (instead of the other way around) was

A

Copernicus

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39
Q

The scientist who first devised experimental tests to demonstrate the validity of the heliocentric model of the solar system was

A

Galileo

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40
Q

In Copernicus’ day, people were worried about the idea that the celestial sphere seemed to turn around us once a day because the Earth rotates. They argued that if the Earth were to rotate so fast, it should fly apart. What was one response Copernicus had to this worry?

A

Copernicus argued that the idea that the much larger celestial sphere is turning once a day (and the Earth is not) meant that the celestial sphere would be torn apart even more. 

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41
Q

What portion of the celestial sphere can be observed from the North Pole during the course of a year? (Answer in percentages)

A

50%

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42
Q

During a retrograde loop of Mars, will Mars appear brighter than usual in the sky, about average in brightness, or fainter than usual in the sky?

A

Brighter

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43
Q

Given a figure where the Earth is in its standard North and South positioning. Let’s say there are 5 latitudes labeled, A-E. A being the North Pole, E being the South, C being the Equator, and B, and d being two mid-latitudes.

Where would a person be if they observed that all stars are visible over the course of a year?

A

C, the Equator

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44
Q

Given a figure the Earth is in its standard North and South positioning. Let’s say there are 5 latitudes labeled, A-E. A being the North Pole, E being the South, C being the Equator, and B, and E being two mid-latitudes.

Where would the person be if they observed that the stars rise and set perpendicular to the horizon?

A

C, the Equator

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45
Q

A woman lives at latitude 33° in the Northern Hemisphere.

How high above the horizon (in degrees) is the north celestial pole where this woman lives?

A

33.00 degrees

46
Q

The Moon moves across the sky relative to the background stars at approximately 0.5 degrees per hour. If you look at the Moon in the early part of the evening and then spend 2.5 hours in the library studying for an astronomy exam, how far, in degrees, will the Moon have moved relative to the stars when you leave the library?

A

Angular distance = 1.250 degrees

46
Q

A woman lives at latitude 33° in the Northern Hemisphere.

How far is it (in degrees) from the north celestial pole to the zenith where this woman lives?

A

57.00 degrees

47
Q

Astronomers subdivide degrees down into arcminutes and arcseconds.

Suppose a constellation has an angular width of 25 degrees. How many arcminutes does this equate to? With that angle, how many arcseconds are in it?

A

25 degrees = 1500 arcmin
25 degrees = 9.000×10^(4) arcsec

48
Q

The ancient Greeks had good arguments for why the Earth must be round. When the Earth’s shadow is visible on the Moon during a lunar __________, it always shows a round shape. In the northern hemisphere, the height of the north star _________ as a traveler moves south. The size of the round Earth was measured by ____________; he measured the angle that sunlight made with a vertical line in different cities at the same time on the same day. In the second century BCE, Hipparchus measured and described __________, the idea that the north celestial pole (the point around which stars in the sky seem to turn) had changed its position over long periods of time. The astronomer ___________ made a geometric model of our solar system, with the Earth in the center, and circles upon circles to explain the movements of the planets in the sky.

A
  1. The ancient Greeks had good arguments for why the Earth must be round. When the Earth’s shadow is visible on the Moon during a lunar ECLIPSE, it always shows a round shape.
  2. In the northern hemisphere, the height of the north star DECREASES as a traveler moves south.
  3. The size of the round Earth was measured by ERATOSTHENES; he measured the angle that sunlight made with a vertical line in different cities at the same time on the same day.
  4. In the second century BCE, Hipparchus measured and described AXIAL PRECESSION, the idea that the north celestial pole (the point around which stars in the sky seem to turn) had changed its position over long periods of time.
  5. The astronomer CLAUDIUS PTOLEMY made a geometric model of our solar system, with the Earth in the center, and circles upon circles to explain the movements of the planets in the sky.
49
Q

The Sun’s apparent path around the celestial sphere is called

A

the ecliptic.

50
Q

From horizon to opposite horizon, the sky takes up how much angular distance?

A

180 degrees.

51
Q

The 17th century astronomer who kept a roughly 20-year continuous record of the positions of the Sun, Moon, and planets was:

A

Tycho Brahe

52
Q

The scientist who formulated the three laws of planetary motion by analyzing the data on the precise location of planets in the sky was:

A) Galileo Galilei
B) Isaac Newton
C) Johannes Kepler
D) Tycho Brahe

A

Johannes Kepler 

53
Q

When a planet, in its orbit, is closer to the Sun, it:

A) Moves slower than average
B) Moves faster than average
C) Remains at a constant speed
D) Changes direction randomly

A

Moves faster than average

54
Q

We now know that the orbit of a stable planet around a star like the Sun is always in the shape of:

A) A circle
B) A square
C) An ellipse
D) A triangle

A

An ellipse

55
Q

According to Kepler’s third law, there is a relationship between the time a planet takes to revolve around the Sun and its

A

distance from the Sun

56
Q

When NASA and a group of astronomers sent up a spacecraft designed to find planets orbiting other stars, they named it after Kepler. Why was this an appropriate name?

A

Kepler figured out the rules of planetary motion, which planets in our solar system and planets elsewhere must obey

57
Q

Which of the following statements about the force of gravity is FALSE?

A) Its strength is directly proportional to the mass of the objects involved.
B) Its strength is inversely proportional to the distance between the objects.
C) Its strength is inversely proportional to the mass: the more mass, the less gravity.
D) Gravity acts between any two objects that have mass.

A

its strength is inversely proportional to the mass: the more mass, the less gravity 

58
Q

An astronomy textbook, when printed out, weighs four pounds on the surface of the Earth. After finishing your course, you arrange for NASA to shoot it into space. When it is twice as far from the center of the Earth than when you were reading it, what would it weigh?

A) 4 lbs
B) 2 lbs
C) 1 lb
D) 0.5 lbs

A

1 lb

59
Q

Astronomers discover a new comet that orbits the Sun but has its aphelion (the furthest point in its orbit) beyond Neptune. Astronomers studying this comet have the right to expect that it:

A) Will follow Kepler’s laws of planetary motion
B) Will follow Newton’s laws of motion
C) Will not be affected by the gravity of the Sun
D) Will have a circular orbit

A

will follow Newton’s laws of motion

60
Q

In Newton’s Law of Gravity, the force of gravity goes up as the:

A) Mass of the objects increases
B) Distance between the objects decreases
C) Volume of the objects increases
D) Density of the objects increases
E) Mass of objects increases and Volume of the objects increases
F) Mass of the objects increases and Distance between the objects decreases

A

F) Mass of the objects increases and Distance between the objects decreases

61
Q

To leave the gravitational pull of the Earth, and explore other planets, satellites must have at least:

A

escape velocity

62
Q

Let’s say a orbit has a semimajor axis of 1 (in arbitrary units).

Which of the following orbits would have a shorter orbital period?

A) Circular orbit with radius 2
B) Circular orbit with radius 1
C) Elliptical orbit with a semimajor axis of 3
D) Elliptical orbit with a semimajor axis of 2

A

B) Circular orbit with radius 1

63
Q

In 1996, astronomers discovered an icy object beyond Pluto that was given the designation 1996 TL 55. it has a semimajor axis of 84 AU.

What is its orbital period in years according to Kepler’s third law?

A

Period = 769.9 years

64
Q

Imagine if there were a planet orbiting the Sun with an orbital period P = 52 years.

What is the average distance, a, between this planet and the Sun? Give your answer in astronomical units.

A

13.93 AU

65
Q

True or False: According to Newton’s second law, the acceleration of any object must always change, under all circumstances.

A

FALSE

66
Q

True or False: Astronauts about the International Space Station orbiting our planet are “weightless” because their distance from the Earth’s gravity is so large.

A

FALSE

67
Q

True or False: Astronauts in the International Space Station don’t feel their weight because they are falling around the Earth.

A

TRUE

68
Q

True or False: To figure out his law of universal gravitation, Newton had to make sure that whatever rule he came up with fit with Kepler’s laws of planetary motion.

A

TRUE

69
Q

The latitude of the Earth’s equator is

A

0 degrees

70
Q

If you could see the new moon, at what time of day (roughly) would it rise?

A

at sunrise

71
Q

A dashing Romanian count asks his sweetheart to marry him. She says she will give her reply when the Moon is full. If he asked when the Moon was at first quarter, how long will he have to wait?

A

about a week

72
Q

A friend of yours who takes her astronomy class very seriously challenges you to a contest to find the thinnest crescent moon you can find just after new moon? What time of day is best for looking for this very thin crescent?

A

just as the sun is setting, or just after

73
Q

Why does the Moon show phases in the course of a month?

A

the angle the Moon makes with the Sun changes and we see differing amounts of reflected sunlight 

74
Q

From a particular location on Earth, why can we see many more total eclipses of the Moon than total eclipses of the Sun?

A

a total lunar eclipse is visible over a much larger part of the Earth’s surface than a total solar eclipse

75
Q

What phase of the Moon must it be to have a lunar eclipse?

A

Full moon

76
Q

Let’s say we view the Moon’s orbit as seen from above Earth’s North Pole. What position (indicated by roman numeral) would the moon be one week after observers on Earth see a solar eclipse?
Assume that the sunlight is coming from the left, and the top of the Earth is I, right side of Earth is III, bottom of the Earth is V, and left of the earth (where sunlight is coming from) is VII. (Fill in the rest of the diagonals with roman numerals as well.

A

V

77
Q

Imagine you are looking at the Earth such that you can see the moon orbiting around it. (From a sort of side angle view of the earth so that you can see the southern and northern hemisphere, but a little higher up so you can see the moon orbit behind the Earth). It orbits counter-clockwise, and sunlight is emitted from the left. The orbit is labeled (including diagonal diagonal positions), starting from the left, and going counter-clockwise: A (left), B, C (bottom), D, E (right), F, G (top), H.

Suppose you looked up in the sky from the Northern Hemisphere and observed the Moon illuminated with the most of the entire left side dark, and a small crescent on the right side illuminated. At which lettered position in its orbit is the Moon located at this moment?

What phase is the Moon in when it appears this way?

A

B, Waxing Crescent

78
Q

The Moon orbits Earth at an average distance of 384,000 km and completes one sidereal orbit (with respect to the stars) in about 27.3 days.

Based on these two numbers, what is its average orbital speed? Express your answer in km/s.

A

v = 1.023 km/s

79
Q

What does a waning crescent look like if viewed from the Southern Hemisphere?

A

During this phase, the moon is less than half illuminated but more than not illuminated, giving it a thing, backwards “C” shape on the right side of the moon. During this time, the moon rises in the early hours and fades as the sun rises, marking the last visible phase of the lunar cycle before it renews.

80
Q

What does a waning gibbous look like if viewed from the Southern Hemisphere?

A

During this phase, the moon is more than half illuminated but less than fully illuminated, giving it a rounded shape on the right side of the moon. Observers in the Southern Hemisphere will notice that the moon is high in the sky during the late evening and early morning, and it appears to move from east to west.

81
Q

Match up each Moon phase with the approximate rise time of that phase. (As seen from the Northern Hemisphere.)

12am:
3am:
6am:
9am:
12pm:
3pm:
6pm:
9pm:

A

12am: Last Quarter — Left half illuminated, 50%, waning.
3am: Waning Crescent — Small left sliver illuminated, less than 50%, waning.
6am: New Moon — Not visible, 0% illumination.
9am: Waxing Crescent — Small right sliver illuminated, less than 50%, waxing.
12pm: First Quarter — Right half illuminated, 50%, waxing.
3pm: Waxing Gibbous — Mostly right side illuminated, more than 50%, waxing.
6pm: Full Moon — Fully illuminated, 100%.
9pm: Waning Gibbous — Mostly left side illuminated, more than 50%, waning.

82
Q

True or False: The same side of the Moon (with the same craters) is always in sunlight and the other side of the Moon is always in darkness.

A

FALSE

83
Q

True or False: A total eclipse of the Sun occurs at those times when the umbra of the Moon’s shadow reaches the surface of Earth.

A

TRUE

84
Q

What would you have to change about the Earth to stop our planet from having significantly different seasons?

A

The tilt of the axis

85
Q

The Earth is closest to the Sun in which month of the year?

A

January 

86
Q

Which of the following is an important part of the reason it is hotter in summer in North America than in winter?

A) The Sun’s rays hit the Earth more directly in the summer and spread out less
B) The Earth’s distance from the Sun is shorter in summer
C) The Sun is closer to the Earth during winter
D) The Earth experiences longer nights in summer

A

the Sun’s rays hit the Earth more directly in the Summer, and spread out less

87
Q

If there really were a Santa Claus at the North Pole, what would the cycle of the seasons be like for him and Mrs. Claus?

A) Four equal seasons of light and dark
B) Six months of light, followed by six months of darkness (or at least dark twilight)
C) Constant daylight throughout the year
D) Twelve months of darkness

A

six months of light, followed by six months of darkness (or at least dark twilight) 

88
Q

Which of the following statements about the International Date Line is correct?

A) When crossing from west to east, you must decrease the date by one day
B) When crossing from east to west, you must decrease the date by one day
C) The International Date Line is a straight line that runs along the 180th meridian
D) The International Date Line is always located at the same longitude

A

When crossing from west to east, you must decrease the date by one day 

89
Q

When the Sun and Moon are lined up and pull together, the tides they raise are called:

A) Neap tides
B) Spring tides
C) Tidal waves
D) High tides

A

Sprint tides

90
Q

Imagine that Earth had no axial tilt. How would this affect our view of eclipses (solar and lunar)?

A) We would continue to see solar and lunar eclipses in the same way we currently do.
B) Eclipses would occur less frequently.
C) Eclipses would only be visible from the equator.
D) Eclipses would be much more common and visible everywhere.

A

We would continue to see solar and lunar eclipses in the same way we currently do.

91
Q

Due to dynamical effects related to tides, the Moon is slowly moving away from Earth at a rate of about 3.8 cm per year.

How long will it take the Moon to move away by a distance equal to its diameter? Express your answer in millions of years.

A

91.47
millions of years

92
Q

Arrange the following bands of the electromagnetic spectrum in order by frequency, highest to lowest:

A) Infrared, violet, red, X-ray, radio
B) X-ray, violet, red, infrared, radio
C) Radio, infrared, violet, X-ray, red
D) Red, infrared, radio, X-ray, violet

A

X-ray, violet, red, infrared, radio.

93
Q

Arrange the following bands of the electromagnetic spectrum in order by wavelength, longest to shortest:

A) Gamma ray, ultraviolet, blue, red, microwave
B) Microwave, red, blue, ultraviolet, gamma ray
C) Red, blue, ultraviolet, microwave, gamma ray
D) Ultraviolet, microwave, gamma ray, red, blue

A

Microwave, red, blue, ultraviolet, gamma ray.

94
Q

Arrange the following bands of the electromagnetic spectrum in order by energy, highest to lowest:

A) Radio, infrared, red, violet, X-ray
B) X-ray, violet, red, infrared, radio
C) Infrared, red, radio, violet, X-ray
D) Violet, X-ray, infrared, red, radio

A

X-ray, violet, red, infrared, radio

95
Q

The light which allows you to see this very interesting exam is made up of waves. In these waves, the distance between crests is called the:

A

wavelength

96
Q

How fast do electromagnetic waves travel?

A

at the speed of light

97
Q

In the future, several students living on board a space station decide to have a race among different types of electromagnetic radiation. Which of the following travels through space the fastest?

A

you can’t fool me, all of these travel through space at the same speed 

98
Q

A Hertz is

A

a unit of frequency

99
Q

Not all wavelengths of electromagnetic radiation can penetrate the Earth’s atmosphere. Of the following types of waves that come from space, which one are you likely to be able to detect most easily from our planet’s surface?

A) Gamma rays
B) Ultraviolet rays
C) X-rays
D) Radio waves of the wavelength that carry FM broadcasts

A

Radio waves of the wavelength that carry FM broadcasts

100
Q

An idealized object that does not reflect or scatter any radiation that hits it, but simply absorbs every bit of radiation that falls on it is called:

A

a blackbody 

101
Q

An astronomer discovers a new star and wants to measure its temperature. She would typically do this by:

A

making a blackbody curve and finding the wavelength of the peak (maximum) 

102
Q

Wien’s Law relates the wavelength at which a star gives off the greatest amount of energy to the star’s:

A) Distance from Earth
B) Size
C) Temperature
D) Luminosity

A

Temperature

103
Q

Why do different types of atoms (elements) give off or absorb different spectral lines?

A

because the spacing of the energy levels is different in different atoms 

104
Q

Let’s say you have a hydrogen spectrum from a source that is stationary with respect to the observer (you) (such that the wavelength is increasing from left to right).

Suppose the source was moving toward you at a high speed. What would you expect the new observed spectrum to resemble?

A

Black bands and spectrum would be all shifted toward the left for shorter wavelengths.

105
Q

A carrier wave on a campus radio is broadcasting at a frequency f = 92 MHz.

What is the wavelength of the carrier wave of this radio in meters?

A

Wavelength = 3.261m

106
Q

Your astronomy instructor is pointing a red laser beam with a wavelength of 650.5 nm at a power point presentation you are reviewing in class.

What is the frequency in hertz of the red laser beam?

A

4.612×10^(14) Hz

107
Q

The maximum light emitted by a star is at a wavelength λ_max = 312 nm.

What is the temperature T in Kelvin of the star?

A

9288 K

108
Q

An astronomer takes a spectrum of a star and finds an absorption line of sodium, which is measured at 589.0 nm in a lab on Earth. He measures that line to be 588.9 nm.

How fast is the star moving relative to us in m/s?

A

5.093×10^(4) m/s

109
Q

An astronomer studies a newly discovered star and determines that it has a luminosity 1.1 times that of the Sun, where the Sun’s luminosity is 3.8 × 10^(26) W. Further analysis reveals that this star’s apparent brightness is 6.9 × 10^(-13) W/(m^(2)).

a) Calculate this star’s distance, in km.

b) Express this star’s distance in light-years (1 light-year = 9.5 × 10^(12) km).

A

a) 6.943 × 10^(15) km
b) 730.9 ly

110
Q

Suppose Star A and Star B have the same surface temperature but Star A is 73237 times as luminous.

How many times larger is Star A than Star B?

A

Factor = 270.6

Astronomy Assignments and Quizzes (2 decks)

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