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When is/was gravitational contraction an important energy-generation mechanism for the Sun?

when the Sun was being formed from a collapsing cloud of gas

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 is the Sun made of?

70 percent hydrogen, 28 percent helium, 2 percent other elements

What is the average temperature of the surface of the Sun?

6,000 K

Which is closest to the temperature of the core of the Sun?

10 million K

From the center outward, which of the following lists the "layers" of the Sun in the correct

core, radiation zone, convection zone, photosphere, chromosphere, corona

Which layer of the Sun do we normally see?


The core of the Sun is

hotter and denser than the surface.

How does the Sun generate energy today?

nuclear fusion

How do human-built nuclear power plants on Earth generate energy?

nuclear fission

Hydrogen fusion in the Sun requires a temperature (in Kelvin) of

millions of degrees.

At the center of the Sun, fusion converts hydrogen into

helium, energy, and neutrinos.

Suppose you put two protons near each other. Because of the electromagnetic force, the two
protons will

repel each other

The overall fusion reaction by which the Sun currently produces energy is

4 H ? 1 He + energy.

Why must the Sun's rate of fusion gradually rise over billions of years?

Fusion reactions decrease the overall number of particles in the core, causing the core to
shrink, converting gravitational potential energy into thermal energy, and increasing the
rate of fusion.

Studies of sunquakes, or helioseismology, have revealed that

our mathematical models of the solar interior are fairly accurate

Which statement best describes the solar neutrino problem?

Solar neutrinos have been detected, but in fewer numbers than predicted by theoretical

What is a possible solution to the solar neutrino problem?

The electron neutrinos created in the Sun change into another type of neutrino that we do
not detect

The light radiated from the Sun's surface reaches Earth in about 8 minutes, but the energy of
that light was released by fusion in the solar core about

a million years ago.

What happens to energy in the convection zone of the Sun?

Energy is transported outward by the rising of hot plasma and the sinking of cooler

Which of the following statements about the sunspot cycle is not true?

The rate of nuclear fusion in the Sun peaks about every 11 years.

Approximately, what basic composition are all stars born with?

three-quarters hydrogen, one-quarter helium, no more than 2 percent heavier elements

Since all stars begin their lives with the same basic composition, what characteristic most
determines how they will differ?

mass they are formed with

A star's luminosity is the

total amount of light that the star radiates each second

If the distance between us and a star is doubled, with everything else remaining the same, the

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

Suppose you measure the parallax angle for a particular star to be 0.1 arcsecond. The distance
to this star is

10 parsecs.

Suppose that you measure the parallax angle for a particular star to be 0.5 arcsecond. The
distance to this star is

2 parsecs.

The spectral sequence sorts stars according to

surface temperature.

The spectral sequence in order of decreasing temperature is


Suppose you see two main-sequence stars of the same spectral type. Star 1 is dimmer in apparent
brightness than Star 2 by a factor of 100. What can you conclude? (Neglect any effects that
might be caused by interstellar dust and gas.)

Star 1 is 10 times more distant than Star 2.

Which of the following terms is given to a pair of stars that we can determine are orbiting each
other only by measuring their periodic Doppler shifts?

spectroscopic binary

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

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 left

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

upper right

You observe a star in the disk of the Milky Way, and you want to plot the star on an H-R
diagram. You will need to determine all of the following, except the

rotation rate of the star.

On the main sequence, stars obtain their energy

by converting hydrogen to helium

A star of spectral type O lives approximately how long on the main sequence?

1 million years

A star of spectral type G lives approximately how long on the main sequence?

10 billion years

Why are Cepheid variables so important for measuring distances in astronomy?

Their luminosity can be inferred from their period.

Which of the following statements about an open cluster is true?

All stars in the cluster are approximately the same age.

Cluster ages can be determined from

main sequence turnoff.

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