Astronomy Chap 10-12

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Which two factors primarily determine the characteristics of a star?

its mass and its stage of life

Based on the definition of apparent brightness, which units are appropriate for its measurement?

watts per square meter

Star A is identical to Star B, except that Star A is twice as far from us as Star B. Therefore:

Both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A.

distance in parsecs =

1/(parallax angle in arcsecond).

The spectral type of a star can be used to determine:

its surface temperature



To calculate the masses of stars in a binary system, we must measure their

orbital period and average orbital distance

Careful measurements reveal that a star maintains a steady apparent brightness at most times, except that at precise intervals of 73 hours the star becomes dimmer for about 2 hours. The most likely explanation is that:

the star is a member of an eclipsing binary star system

Which groups of stars are extremely bright and emit most of their radiation as ultraviolet light?

Hotter & more luminous main sequence stars

Which stars have the longest main-sequence lifetimes?

low-mass stars have the longest lifetimes

You observe a star and you want to plot it on an H-R diagram. You will need to measure all of the following:

luminosity, temperature, and distance

The approximate main-sequence lifetime of a star of spectral type O is

3 million years

How did astronomers discover the relationship between spectral type and mass for main sequence stars?

By measuring the masses and spectral types of main-sequence stars in binary systems.

Which two processes can generate energy to help a star maintain its internal thermal pressure?

nuclear fusion and gravitational contraction

Our Sun is considered to be a:

low-mass star

Which process is required to allow a gravitationally-collapsing gas cloud to continue to collapse?

The cloud must radiate much of its thermal energy.

Which characteristics of a protostellar system are strongly affected by the star's angular momentum?

the strength of protostellar winds
the existence of protostellar jets
the formation of a protostellar disk

A main-sequence star is _______ and ________ than it was as a protostar

hotter & dimmer

Brown Stars never


What data provides evidence that helps us understand the life tracks of low-mass stars?

H-R diagrams of globular clusters

Why is a 1 solar-mass red giant more luminous than a 1 solar-mass main sequence star?

Fusion reactions are producing energy at a greater rate in the red giant.

Carbon fusion occur in high-mass stars but not in low-mass stars because:

the cores of low-mass stars never get hot enough for carbon fusion

Which event marks the beginning of a supernova?

The sudden collapse of an iron core into a compact ball of neutrons

At the end of a high-mass star's life:

it produces new elements through a series of helium capture reactions

Which is more common: a star blows up as a supernova, or a star forms a planetary nebula/white dwarf system?

Planetary nebula formation is more common.

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

It was important when the Sun was forming from a shrinking interstellar 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.

How does the Sun's mass compare to Earth's mass?

The Sun's mass is about 300,000 times the mass of the Earth

What 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.

The Sun's surface seethes and churns with a bubbling pattern. Why?

We are seeing hot gas rising and cool gas falling due to the convection that occurs beneath the surface.

Every second, the Sun converts about 600 million tons of hydrogen into 596 million tons of helium. The remaining 4 million tons of mass is:

converted to an amount of energy equal to 4 million tons times the speed of light squared

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.

Why does the Sun emit neutrinos?

Fusion in the Sun's core creates neutrinos

Why do sunspots appear dark in pictures of the Sun?

They actually are fairly bright, but appear dark against the even brighter background of the surrounding photosphere.

How can we best observe the Sun's chromosphere and corona?

The chromosphere is best observed with ultraviolet telescopes and the corona is best observed with X-ray telescopes.

The intricate patterns visible in an X-ray image of the Sun generally show :

extremely hot plasma flowing along magnetic field lines

How can we measure the strength of magnetic fields on the Sun?

By looking for the splitting of spectral lines in the Sun's spectrum

Why does the Sun shine?

As the Sun was forming, gravitational contraction increased the Sun's temperature until the core become hot enough for nuclear fusion, which ever since has generated the heat that makes the Sun shine.

What is the sun's surface temp?

5800 K

Earth's upper atmosphere tends to _______ during solar maximum


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