Astronomy Final

Which of the following properties is used to distinguish between the core, mantle and crust of a planet?

Density

The lithosphere of a planet is the layer that consists of

the rigid rocky material of the crust and uppermost portion of the mantle

 Why do terrestrial planet cores contain mostly metal? 

 Metals are denser than rocks, so they sank to the center when the interiors were molten. 

Which of the following best describes differentiation in planetary geology?

 Gravity separates molten materials according to density. 

Which internal energy source is the most important in continuing to heat the terrestrial planets today? 

 Radioactivity 

 What are the three main sources of internal heat for terrestrial planets? 

 Accretion, differentiation, and radioactivity 

Which of the following best describes tectonics?

 The disruption of a planet's surface by internal stresses 

How does the greenhouse effect work? 

Greenhouse gases transmit visible light, allowing it to heat the surface, but then absorb infrared light emitted by the surface, trapping the heat near the surface. 

Why is the sky blue?

Air molecules scatter blue light more effectively than red light. 

Why are sunsets and sunrises red? 

Sunlight must pass through more atmosphere to reach our eyes at those times, so more blue light is scattered away. 

Ridges in the middle of the ocean are places where 

hot mantle material rises upward and spreads sideways, pushing the plates apart 

Which of the following can act like a long-term "thermostat" that helps keep Earth's average temperature fairly stable? 

The carbon dioxide cycle that moves carbon dioxide between Earth's atmosphere, oceans, and rock 

Where did the molecular oxygen in Earth's atmosphere come from? 

Photosynthesis by living organisms 

What conditions are thought to be necessary for a terrestrial planet to have a strong magnetic field? 

Both a molten metallic core and reasonably fast rotation 

Approximately how large (across) is an impact crater compared to the size of the impactor?

10 times larger 

Volcanism is more likely on a planet that 

has high internal temperature 

Which terrestrial world has the highest average surface temperature? 

Venus

Which of the following is not a greenhouse gas? 

Molecular oxygen (O2) 

A planet with a higher reflectivity will do which of the following? 

Reflect more light and absorb less light 

 Which jovian planets have compositions dominated by hydrogen compounds such as methane, ammonia, and water? 

 Uranus and Neptune

Based on the graph above, what would be the approximate radius of a hydrogen/helium planet with a mass one-tenth that of Jupiter? 

 About 0.7 times the radius of Jupiter 

 Why is Saturn almost as large in radius as Jupiter despite its smaller mass? 

Jupiter's greater mass compresses it more, thus increasing its density. 

Based on models, how does Jupiter's core compare in size and mass to Earth? 

It is about the same size, but has about 10 times as much mass as Earth.

What is Jupiter's Great Red Spot?

A giant storm that is about twice as wide as the planet Earth

Why does Jupiter have several distinct cloud layers?

Different gases can condense at different altitudes in Jupiter's atmosphere.

Why do Uranus and Neptune appear blue? 

The methane gas in their atmospheres absorbs red light. 

The largest Jovian moons have sizes comparable to Mercury. Why do they have an icy composition compared to Mercury's rocky composition? 

They formed beyond the frost line, where ices were more abundant than metals and rock. 

Where do scientists think that Jupiter's strong magnetic field is generated? 

In its metallic hydrogen layer 

Why are there no impact craters on the surface of Io? 

All of Io's impact craters have been buried by lava flows. 

What mechanism is most responsible for generating the internal heat of Io that drives volcanic activity?

Tidal heating 

Based on the given densities, which of these jovian moons contain the greatest percentage of rocky material and the smallest percentage of icy material?

Io (density = 3.57 grams/cc) 

Which of the following moons has the most substantial atmosphere? 

Titan

What is the most important reason why an icy moon is more likely to be geologically active than a rocky moon of the same size?

Ice is less rigid and has a lower melting point than rock. 

You are somewhere in the solar system. It's much colder than Earth, and you are airborne in the planet's atmosphere, with blue skies around you. And while you can tell that your planet is rotating fairly rapidly, it is remaining daylight at all times, indicating a very large axis tilt (much larger than Earth's). Where are you? 

Uranus

What two forces are balanced in what we call gravitational equilibrium? 

 Outward pressure and inward gravity 

How does the Sun generate energy today?

Nuclear fusion

How do we know how old the Sun is?

From radiometric dating of solar system meteorites

Where in the Sun do fusion reactions happen?

Only the core

Scientists in the 1800s suggested that the source of the Sun's energy might be gravitational contraction. What was the major flaw of this hypothesis?

This process would power the Sun for only about 25 million years, but geologists already had evidence the Earth was much older than that

What keeps the Sun's outer layers from continuing to fall inward in a gravitational collapse?

Outward pressure due to hot gas

Which of the following quantities is equal to the energy per second generated by fusion in the Sun's core?

The luminosity of the Sun's photosphere

Which of the following is the best answer to the question "Why does the Sun shine?"

The young Sun became hotter through gravitational contraction. Once the core was hot enough, nuclear fusion began and has kept the Sun shining ever since.

We say that the matter in the Sun's interior is a plasma, which means it is

an ionized gas

The core of the Sun is 

hotter and denser than the surface

Based on its surface temperature of 5800 K, most photons that leave the Sun's surface lie in the ________ region of the electromagnetic spectrum

visible

If the Sun's surface were cooler, how would its appearance change? 

It would appear more red

Order the interior layers of the Sun from hottest to coldest

Core, radiation zone, convection zone, photosphere

Which of the following properties of the Sun tells us the rate at which energy is being generated in its core?

Luminosity

Which of the following statements is an inference from a model (rather than an observation)? 

The Sun's core is gradually turning hydrogen into helium

If the Sun's core suddenly shrank a little bit, what would happen in the Sun?

The core would heat up, fusion rates would increase, the core would re-expand.

A salesman attempts to convince you to purchase a "solar neutrino shield" to protect you and your family. (It's even "on sale!") Why do you turn down this excellent offer?

Neutrinos rarely, if ever, interact with other matter

Which of the following best describes why the Sun emits most of its energy in the form of visible light?

Like all objects, the Sun emits thermal radiation with a spectrum that depends on its temperature, and the Sun's surface temperature is just right for emitting mostly visible light.

What do we mean when we say that the Sun is in gravitational equilibrium?

There is a balance within the Sun between the outward push of pressure and the inward pull of gravity.

What do we mean when we say that the Sun is in energy balance?

The amount of energy released by fusion in the Sun's core equals the amount of energy radiated from the Sun's surface into space.

What is a star's luminosity?

The total energy that the star radiates each second

What two things do we need to measure in order to determine a star's luminosity?

Apparent brightness and distance

Suppose the distance to a star was doubled but everything else about the star stayed the same. What would happen to the star's luminosity and apparent brightness?

Luminosity remains the same, but the apparent brightness is decreased by a factor of four.

Stars X and Y have the same luminosity, but star Y is 10 times as far from Earth as star X. How much brighter will star X appear in our sky than star Y?

100 times

Which of the following properties of stars is directly observed (i.e., it can be measured by a calibrated instrument on a telescope, from a single observation without a need for additional calculations)?

Apparent brightness

Star X has a smaller parallax angle than star Y. What can you conclude?

Star X is farther from Earth than star Y.

How do we estimate the surface temperature of a star?

By obtaining its spectrum and classifying the spectral type

Which of the following correctly lists spectral types in order of decreasing temperature (from hottest to coolest)?

OBAFGKM

Star X has spectral type B. Star Y has spectral type M. What can we conclude?

Star X has a higher surface temperature than star Y

Which spectral type represents stars with spectra that peak at the shortest ultraviolet wavelengths? 

O

Which of the following best describes the axes of a Hertzsprung-Russell (H-R) diagram? 

Surface temperature on the horizontal axis and luminosity on the vertical axis 

Based on the H-R diagram shown above, what is the approximate surface temperature of an F star? 

6000 K

Based on the H-R diagram shown above, what is the spectral type of a main-sequence star with a luminosity 100 times greater than that of the Sun?

A

Based on the H-R diagram shown above, what is the approximate luminosity of a main-sequence M star? 

0.01 times that of the Sun

A main-sequence star is observed with a surface temperature of 3500 K and a luminosity 10⁻² times that of the Sun. Based on the H-R diagram shown above, what is the approximate mass of this star?

0.2 times that of the Sun

Based on the H-R diagram shown above, about how long does a main-sequence star of spectral type G spend fusing hydrogen into helium in its core?

10 billion years 

On a Hertzsprung-Russell diagram, where would we find stars that are cool and dim?

Lower right

On a Hertzsprung-Russell diagram, where would we find stars that have the largest radii?

Upper right

On a Hertzsprung-Russell diagram, where on the main sequence would we find stars that have the greatest mass?

Upper right

On a Hertzsprung-Russell diagram, where would we find red giant stars? 

Upper right