Astronomy Test 3

Which layer of the Sun produces the visible light we see?

The photosphere.

What is the approximate density of the Sun compared to other objects?

It is similar to the density of Jupiter.

What is the temperature of the Sun's photosphere?

Approximately 5,800 K.

Why can you not stand on the surface of the Sun?

The Sun does not have a solid surface; the photosphere is a layer of gas.

What is the 'solar constant'?

The amount of solar energy reaching Earth per unit area per unit time.

What natural barrier prevents two protons from combining in the Sun?

Electromagnetic repulsion.

What is the net result of the proton-proton chain?

Four hydrogen nuclei are fused into one helium nucleus, releasing two neutrinos and energy.

What is the critical temperature required to initiate the proton-proton cycle?

Approximately 10 million K.

Which of the fundamental forces is the strongest?

The strong nuclear force.

How does solar energy move from the layer beneath the photosphere to the surface?

Through convection.

What is a major mystery regarding the Sun's corona?

The corona is significantly hotter than the layers of the Sun closer to the interior.

How often do sunspot activity cycles peak?

Approximately every eleven years.

What is a property of neutrinos?

They are almost massless, neutral in charge, and travel near the speed of light.

What is an anti-electron called?

A positron.

How do you calculate the distance of a star in parsecs given its parallax in arcseconds?

Distance (parsecs) = 1 / Parallax (arcseconds).

What are the two most important intrinsic properties used to classify stars?

Luminosity and surface temperature.

What physical property does a star's spectral type measure?

Temperature.

What does a star's color index indicate?

Its temperature.

What is the approximate length of a parsec in light-years?

About 3.3 light-years.

Where do white dwarfs lie on the H-R diagram?

On the lower left portion.

What does the H-R diagram plot?

Luminosity versus surface temperature.

What is the average temperature of interstellar gas and dust?

Approximately 100 K.

What effect does interstellar dust have on visible light?

It dims and reddens the light.

What is interstellar gas primarily composed of?

Hydrogen.

Why do some regions of the Milky Way appear dark?

Interstellar dust obscures the stars behind them.

At what wavelength is neutral hydrogen most easily detected in the radio spectrum?

21 centimeters.

Why is 21-cm radiation important to the study of the Galaxy?

It is emitted by neutral hydrogen and can pass through interstellar dust, allowing astronomers to map the entire Galaxy.

What is the most common molecule in a molecular cloud?

Molecular hydrogen (H2).

What is the critical temperature required for hydrogen fusion in a star's core?

Approximately ten million Kelvin.

What event marks the birth of a star?

The collapse of an interstellar cloud.

What does a cloud fragment that is too small to form a star become?

A brown dwarf.

True or False: Hydrogen is the major gas in the interstellar medium.

True.

True or False: The birth of stars is a battle between gravity and radiation pressure.

True.

True or False: Brown dwarfs are failed stars that never ignite hydrogen fusion.

True.

What element is produced by the helium flash?

Carbon.

In terms of stellar evolution, what is the ultimate fate of gravity?

Sooner or later, gravity wins.

What temperature is required to fuse helium into carbon?

100 million Kelvin.

What forces a star like the Sun to evolve away from the main sequence?

The depletion of hydrogen fuel in the core.

What stage does a star spend the majority of its life in?

The main sequence stage.

Why does a low-mass star become brighter after running out of core hydrogen?

The core contracts, which raises the temperature and expands the region of hydrogen shell-burning.

What is the final evolutionary stage of a Sun-like star?

White dwarf.

What are black dwarfs?

Cooled-off white dwarfs that no longer emit visible light.

Why do high-mass stars die more violently than low-mass stars?

They generate immense heat and their cores collapse very suddenly.

True or False: About 90% of a star's life is spent on the main sequence.

True.

What happens if mass is added to a 1.4 solar mass neutron star until it exceeds 3 solar masses?

It will collapse to become a black hole.

What is the approximate density of a neutron star?

It is comparable to the density of an atomic nucleus (roughly 10^17 kg/m^3).

Who received the Nobel Prize for relating pulsars to neutron star formation?

Anthony Hewish.

What are two important physical properties of young neutron stars?

Extremely rapid rotation and a strong magnetic field.

What can be detected from matter that has crossed the event horizon of a black hole?

Nothing.

What is the key to identifying a black hole candidate in a binary system?

The unseen companion must have a mass significantly higher than the limit for a neutron star.

True or False: Stars between 8 and 25 solar masses will produce neutron stars when they collapse.

True.

True or False: All pulsars are neutron stars, but not all neutron stars are pulsars.

True.