Astronomy Midterm 1

Which of the following is not equivalent to 20 km?

2×10^7 cm

Which is the smallest number?

A. 1.2 x 10^(-7)

B. 0

C. 1.2 x 10^(-12)

D. 1.2 x 10^8

0

When we say “We are children of stars,” what do we mean?

The atoms in our body are made by stars

Which statement best describes the scale of the Milky Way Galaxy?

It contains hundreds of billions of stars.

Which object is part of the Milky Way Galaxy?

The Solar System

Which statement is correct about stars in the same constellation?

They may be extremely far apart in space, even though they appear close together in the sky.

What is a correct description of the Big Dipper we see in the sky?

An asterism within Ursa Major (Big Bear)

Why do the stars in a constellation gradually change their pattern in the sky over many thousands of years?

Stars move through space relative to one another

Why does the Sun set in the west?

Earth rotates on its axis

In the heliocentric model, why does Mars appear to undergo retrograde motion?

Earth passes Mars in its smaller, faster orbit

Where on Earth are all stars above the horizon at one time or another?

Equator

In ancient times, how did people primarily tell the difference between planets and stars?

The planets moved relative to the stars

Which observation was especially difficult to explain with a simple Earth-centered model in which all objects move in perfect circles around Earth?

Retrograde motion of planets

Why do constellations appear almost unchanged in the sky compared with 10 years ago?

The stars are very far away, so their motion is not noticeable over human lifetimes

Which motion makes constellations appear to rise in the east and set in the west each night?

Earth’s rotation

Orion is visible in the evening sky during winter but not during summer. What is the main reason?

Earth’s revolution around the Sun makes the nighttime side face different directions in space during the year

If the Earth's axis were perpendicular to the plane of its orbit around the Sun, there would be no ___________

seasons

According to the geocentric model, how do the Sun, Moon, and stars move?

In circular orbits around Earth

Which statement correctly compares the geocentric and heliocentric models?

The geocentric model places Earth at the center; the heliocentric model places the Sun near the center of the solar system

During one night, a star moves 45 degrees across the sky. About how much time has passed?

3 hours

The eccentricity of the Earth's orbit around the Sun is 0.017, and the semi-major axis of its orbit is 1 AU. What is the distance from the Sun when the Earth is at its closest in AU?

0.98 AU

A star rises at 10:00 PM tonight. About what time will it rise one month from now?

8:00 pm

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

near the South Pole

As a planet moves in its orbit, how does its speed change?

It moves faster when closer to the Sun and slower when farther away.

Which statement does not describe Copernicus's Heliocentric model?

It explains why the Earth has seasons

Jupiter orbits the Sun with a period of approximately 11.86 Earth years. What is the semi-major axis of Jupiter in astronomical units (AU)?

5 AU

Consider two orbiting asteroids in the Solar System with the following orbital properties. What will their orbital periods be? Assume that both asteroids have the same mass.

The orbital period of Asteroid A is the same as that of Asteroid B

Which of the following objects has an apparent motion with retrograde loops?

None of these

Venus’ orbital period is 0.72 years. How does its orbital period compare to that of Earth?

Venus takes about three-quarters as long as Earth to complete one orbit around the Sun.

In looking through historical records, you find a reference to a comet that reappears every 27 years. From this you can determine the semi-major axis of the comet's orbit. What is it?

9 AU

The eccentricity (e) of an ellipse is the ratio of the distance from the center to the foci, "c", to the semi-major axis (a), i.e., e = c/a. Consider an asteroid orbiting the Sun with the following orbital parameters: a = 2.00 AU, P = 2.83 yr, and e = 0.2. At aphelion (the farthest from the Sun), how far from the Sun is the asteroid in units of AU?

2.4 AU

The mass of an asteroid is about 95 times smaller than the Moon's mass. What is the ratio of the gravitational force the asteroid exerts on the Moon to the gravitational force the Moon exerts on the asteroid?

1 to 1

If the Sun were suddenly replaced by a solar-mass black hole, its gravitational pull on the Earth would _______

Remain the same

The acceleration of a comet due only to the Sun’s gravity always points _________________

Toward the Sun

If we move a GPS satellite to a new, higher altitude above Earth, the satellite would __________

lower orbital speed

A giant asteroid is approaching the Earth at a speed of 50 km/sec from a distance of 3 x 10^5 km away. How long will it take to hit the Earth? Assume that the Earth is not moving.

1.7 hr

Earth moves faster in its orbit during January than during July. What is the best explanation?

Earth is closer to the Sun in January

An asteroid has an orbital period of 8 years. What is its average distance from the Sun?

4 AU

If you drop a blue ball and a red ball from your dorm window, what will their speeds be after 5 seconds, according to Galileo’s findings? The blue ball is twice as heavy as the red ball. The Earth's gravitational acceleration is g = -9.8 m/s

Blue ball: 49 m/sec, red ball: 49 m/sec

A satellite moves in an elliptical orbit around Earth. At what point is its speed greatest?

At the point closest to Earth

In Astronomy, almost all information from celestial
objects is carried by light. The speed of light is finite: 𝑐 =
300,000 km/sec. Convert this value to scientific
notation

3 x 10^5 km/sec

Why do astronomers use constellations?

To help describe an object’s approximate location in the sky

What is the best description of a constellation?

An officially defined region of the sky

Which statement is correct about stars in the same constellation?

They are very far apart in space

Why do astronomers use catalog designations?

a) There are too many astronomical objects to give
each one a common name.
b) They help astronomers identify the same object
without confusion.
c) Different surveys can record many objects
systematically.
d) All of the above

All of the above

When you are sitting in the passenger seat of a moving
car, which appears to move more (or faster)?
a) trees

b) mountains

c) the same speed

trees

Which asteroid is closer to us?

A

Which stars we can see at night depends on ___________________

our location on Earth

Why do stars seem fixed relative to one another?

They are extremely far away, so their apparent shifts are usually too small to notice.

Over several hours during one night, how do most stars appear to move across the sky?

Rise in the east and set in the west

Which statement correctly describes the apparent motion of celestial objects in the night sky?

a) Objects near Polaris trace small circles.
b) Objects near the celestial equator trace large arcs.
c) Stars follow the same paths night after night.
d) All of the above

All of the above

Why were epicycles introduced in Ptolemy’s cosmological model?

To explain the retrograde motion of the planets

How does the heliocentric model explain the retrograde motion of the planets?

Differences in orbital speeds cause Earth to pass other planets (or be passed by them), creating an apparent backward motion

Assume that Earth rotates in the opposite direction, but its orbit and axial tilt stay the same. Which statement would be correct?

a) The Sun would rise in the east.
b) The Moon would rise in the west.
c) A day would no longer occur.
d) There is no season on Earth.

The Moon would rise in the west

What causes the different seasons on Earth?

The tilt of Earth’s axis relative to its orbit around the Sun

If a constellation is behind the Sun today, when will it be easiest to see this constellation high in the night sky?

about 6 months from now

The same star rises about 4 minutes earlier each night. A star rises at 9:00 PM tonight. About what time did it rise two weeks ago?

10 pm

A constellation is high in the sky at midnight tonight. About six months later, where will it most likely be at midnight?

Near the Sun and difficult to see at night

What is Tycho Brahe's biggest contribution to astronomy?

His accurate observations of the changing position of planets with respect to the stars

Which statement about ellipses is not correct?

An ellipse has three foci inside the ellipse

The diagram below shows possible orbits of objects orbiting the Sun viewed from above. Which of the three orbits is drawn incorrectly?

B

In Copernicus’s heliocentric model, how do the planets
move?

In circular orbits around the Sun

Halley’s comet reappears every 76 years. What is its semimajor axis in AU?

18 AU

An asteroid and a comet have the same semimajor axis. Ignoring the mass of each object, they have:

the same orbital period

A satellite in orbit around Earth moves faster when it is closer to Earth. Suppose a satellite sweeps out an area of 5x10^(65) km^2 in 2 hours. How much area will it sweep out in the next 1 hour if no external forces act on it?

2.5 x10^(65) km^2

Kepler’s third law of planetary motion can be applied to any planetary system

False

A car increases its speed from 10 m/s to 30 m/s in 5 seconds. What is the car’s acceleration?

(30 m/s – 10 m/s) / 5 sec = 4 m/s^2

Thomas the Tank Engine on a straight railway at the same speed
velocity: speed + direction. Which is true?
a) speed: now vs 2 sec later, change?
b) Thomas’ direction: now vs 2 sec later, change?
c) velocity change?
d) acceleration = 0?

acceleration = 0

Which is true?

Speed change?
Direction change?
Velocity change?
Acceleration = 0?

Speed change

Velocity change

A satellite orbits the Earth in a perfect circular orbit. Do its velocity and acceleration change over time? Hint: The magnitude of its velocity and acceleration is the same. Both velocity and acceleration are vectors.

v: yes, a: yes

A satellite orbits the Earth in a perfect circular orbit. Its velocity and acceleration are shown in the figure below. Is there a force acting on it?

yes

According to Newton’s Second Law, what causes an object to accelerate?

a non-zero net force acting on the object

Why does a rocket move in space?

The exhaust gases push against the rocket, and the rocket pushes back on the gases

If you drop a feather and a steel hammer at the same moment, they should hit the ground at the same instant. Why doesn't this work on Earth, and why does it work on the Moon?

There is no air resistance on the Moon

If you drop a blue ball and a red ball from your dorm window, what will their speeds be after 2 seconds, according to Galileo’s findings? The blue ball is twice as heavy as the red ball and they have the same size.

Blue ball: 19.6 m/sec, red ball: 19.6 m/sec

At Earth’s orbit, 1 AU from the Sun, a solar panel on a spacecraft receives 100 units of sunlight per square meter. The spacecraft then moves to 2 AU from the Sun. How much sunlight does the same solar panel receive per square meter?

25 units

If the distance between two objects is tripled while both masses remain unchanged, what happens to the magnitude of the gravitational force between them?

9 times smaller

Which figure correctly represents the gravitational forces between the two objects?

A

The Earth is not a perfect sphere; its polar radius is about 21 km smaller than its equatorial radius. If you drop a ball from the same altitude at the North Pole and at the Equator, at which location will the ball hit the ground first?

North Pole

An asteroid is moving directly toward Earth. Ignore air resistance. As the asteroid gets closer to Earth, what happens to its speed?

Its speed increases

At its surface, which object has the greatest gravitational acceleration, g?

A

An astronaut has a mass of 80 kg on Earth. On an asteroid where the gravitational acceleration is about 1/100 that of Earth, ____________________. The gravitational acceleration of the Earth is 10 m/sec^2.

his mass is 80 kg and his weight is about 8 N

An exoplanet has about 80% of Earth's mass and about 95% of Earth's radius. What would your weight be on this exoplanet?

about 10% less than on Earth

If Asteroid A is three times as far from the Sun as Asteroid B, which of the following is correct?

Asteroid A will have an orbital period 5.2 times longer than Asteroid B

Consider the Earth-Sun system. According to Newton's laws, which of the following is correct?

The force of the Earth on the Sun is the same as the force of the Sun on the Earth, but opposite in direction

One of the central assumptions in astronomy is that the physical laws of nature on Earth and in the universe _________________.

are the same

Which graph correctly shows the relationship between a planet’s orbital period and its semi-major axis in the Solar System?

D

According to Kepler’s laws, where do comets with highly elongated elliptical orbits spend most of their time?

Near aphelion, far from the Sun

Jupiter sometimes appears to move backward relative to the background stars. What causes this apparent retrograde motion?

Earth passing Jupiter as Earth revolves around the Sun

You are in a spacecraft orbiting 1,000 km above the surface of a planet. The radius of the planet is 1,000 km. How strong is the force of gravity on your spacecraft compared to the one on the surface of the planet?

4 times weaker

Which of the following objects has an apparent motion with retrograde loops?
a) the Sun

b) the Moon

c) Polaris (a star close to the North Pole)
d) none of these

none of these

When a planet temporarily moves westward in the sky over the course of several weeks or months (instead of eastward, as it typically does), we call it:

retrograde motion

In Ptolemy's geocentric model, the planets orbit the Earth and not the Sun. How did this model explain the retrograde motion of planets like Jupiter?

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

A satellite orbits Earth. Which force is larger: Earth pulling on the satellite, or the satellite pulling on Earth?

Both forces are equal in magnitude

If a GPS satellite’s orbital altitude increases, what would its orbital period be?

increases

Which statement is true about man-made satellites orbiting the Earth in highly elliptical orbits?

They move faster when closer to Earth and slower when farther away

If an astronaut takes a 5 kg rock from the Moon to Earth, what happens to its mass and weight? Earth's gravitational acceleration is 9.8 m/s², and the Moon's gravitational acceleration is 1.6 m/s².

Mass = 5 kg; Weight = 49 N

A 2 kg object and an 8 kg object are placed at the same location near Earth. Which statement is correct?

Earth exerts a greater gravitational force on the 8 kg object

A particular constellation is visible high in the southern sky at 10:00 PM tonight in Colombia. One month later, at 10:00 PM, that constellation will appear _______

farther west in the sky

The fact that different constellations are visible at night during different seasons is mainly caused by ________

Earth’s yearly revolution around the Sun