Name __________________________________ Date _________ Per. ______
Unit 7 Review Worksheet
1. Draw a diagram illustrating the structure of the sun. Label each layer.
2. Discuss how the sun produces energy in the core and describe how the sun remains in gravitational equilibrium.
The sun releases energy by hydrogen fusion. During the proton- proton chain, it fuses four hydrogen nuclei into one helium nucleus.
The sun is in equilibrium because the outward radiation pressure balances the inward push of gravity.
3. Describe the transport of energy, from the deep interior of the sun, to when it finally reaches the Earth. Include the various methods of transport.*
Radiation Zone:
Energy transported randomly from atom to atom by photons
Convection Zone:
Energy transported upward by rising hot gas in convective current.
Photosphere:
Visible surface of Sun- energy is given off as visible light. It travels to the earth as photons (radiation).
4. Discuss the nature of the Sun’s magnetic field and its relationship to the various types of solar activity.
The motion of the plasma in the convective zone and the rotation of sun create and twist magnetic fields.
Sunspots occur near strong magnetic fields that burst through the photosphere. The magnetic fields slow convection & cause these cooler, dark patches.
Prominences occur where plasma clings to the magnetic fields that loop up into the sun’s atmosphere.
Coronal holes are areas in the corona where field lines extend out & allow particles to escape as solar wind.
Solar flares (emit x-rays) and CMEs occur when magnetic loops snap.
5. Describe the appearance of the photosphere and the “structure” of a sunspot.
The surface of the photosphere is granulated. The granulation is the bubbling pattern caused by convection below.
Sunspots have a cooler, darker interior called the umbra. This is surrounded by a warmer, lighter region called the penumbra.
6. Describe the sunspot cycle.
The number of sunspots rises and falls in 11-year cycle that has something to do with winding and twisting of Sun’s magnetic field
7. Describe how a star forms from an interstellar cloud. Include a description of each stage ending with when the star enters the main sequence.
A large cloud collapses due to gravity.
As it collapses, it heats up due to conservation of energy. It also begins to spin faster due to conservation of angular momentum. The protostar forms at the center. It is giving off heat but not light at this point.
Collisions between particles flatten the cloud into a disk
When the temperature gets high enough, fusion begins in the core. The protostar becomes a main sequence star.
8. Briefly explain why high-mass stars have shorter lifetimes than low-mass stars. What are the lower end cutoff and upper limit on the mass of a star?*
The range for high mass stars is between 8 and 100 solar masses. These high mass stars have 10 – 100 times the mass (fuel) of a star like our sun which causes greater gravitational pressure so they burn faster. Higher fusion rate causes greater luminosity (1,000 to 1, 000 million times the sun’s luminosity, so they burn up faster.
9. Explain why stars evolve off the main sequence.
Stars leave the main sequence when they’ve used up most of their core hydrogen. The fusion reaction slows so gravity takes over & compresses core.
10. Summarize or illustrate the evolutionary stages followed by a Sun-like star once it leaves the main sequence.
• Once the hydrogen fuel is being used up the core shrinks, begins helium fusion.
• Hot core causes Hydrogen fusion in layer of gas surrounding core.
• Radiation pressure pushes atmosphere out.
• Star swells, and surface cools, becomes a red giant.
• Once helium is used up, gravity compresses core but balanced by electron degeneracy pressure.
• The star’s atmosphere gradually drifts away and forms a planetary nebula.
• The exposed core is a white dwarf.
11. Describe the properties of a white dwarf and explain what supports it. Include the upper mass limit for this type of star.
White dwarfs have a diameter approximately equal to the earth’s diameter.
Electron degeneracy pressure supports them against gravity. The mass of the core is under 1.4 Ms.
12. Explain how white dwarfs in binary systems can become explosively active.
Nova- Occurs in binary system (white dwarf + giant).
Gases from companion form accretion disk & fall on white dwarf surface.
Outer layer of star burns hydrogen again.
13. Describe or illustrate the evolutionary stages of high-mass stars once they leave the main sequence. Include a description of how the star generates energy in the core and which process finally dooms it.
· Hydrogen fuel is being used up.
· Core shrinks, begins helium fusion.
· Core temp so high begin H fusion in layer of gas surrounding core.
· Radiation pressure pushes atmosphere out.
· Star swells.
· Advanced nuclear burning proceeds in a series of nested shells.
· Each reaction takes less time, each time fuel is used – core shrinks more & temp gets higher.
· More & more layers of fusion in shells around core.
· Once iron fusion begins the core collapses in a supernova.
14. Explain how neutron stars are formed. Include a description of how heavy elements are made during the explosion.
Neutron stars are formed when the core of a massive star (1.4 – 3 Ms) collapses.
During the supernova, the shock waves from the rebounding gases blow the star’s layers into space forms a neutron star.
Heaviest elements formed by gases in atmosphere during explosion.
15. Describe the properties of neutron stars. Include a discussion of what supports the star and what the upper mass limit for neutron stars is.
A neutron star is about the same size as a small city. Very dense, teaspoon full weighs more than Mt. Everest. They spin very fast and they have a very strong magnetic field.
Degeneracy pressure of neutrons supports a neutron star against gravity .
Neutron stars form if the mass of the remnant is between 1.4 – 3 Ms.
16. Describe what happens to stars with a mass too big to be a neutron star. What is the name of the spherical surface of space that defines this object? Why can’t we see them?
Stars that are more massive than 8 times Ms (so the core is more than 3 Ms) will collapse to form black holes. The surface that defines the black hole is the event horizon. We can’t see black holes because their gravity is so strong its escape speed is more than the speed of light.
17. Describe the difference between a nova and a supernova.
A nova is the temporary brightening of a WD when fusion ignites on its surface (can happen many times). A supernova is the explosive end of a massive star (occurs only once).
18. Explain how stellar distances are determined using parallax. How far out can this technique be applied? How many stars can be measured with this technique?*
The distance is 1 divided by the parallax angle.
19. So if a star has a parallax angle of 0.5 arcseconds, its distance would be two parsecs.
20. Distinguish between luminosity and apparent brightness, and explain how stellar luminosity is determined.
Luminosity is a measure of how much energy the star is giving off each second.
Absolute magnitude (M) is a measure of the luminosity (it’s a scale, more luminous stars have negative absolute magnitudes). Apparent brightness is how bright the star appears on earth. We can get the luminosity from the star’s apparent brightness and its distance, if it’s known, or its spectrum.
21. Distinguish between apparent magnitude and absolute magnitude. What factors affect the apparent magnitude?
Absolute magnitude (M) – measures how bright it is, in other words, its true luminosity. This depends on the star’s temperature & size. Apparent magnitude (m) measures how bright it looks. This depends on luminosity and distance.
22. Explain the usefulness of classifying stars according to their colors, surface temperatures, and spectral characteristics. What is OBAFGKM?
Absorption lines in a star’s spectrum correspond to a spectral type that reveals its temperature. Based on their temperature or spectral type we know their luminosity (absolute magnitude). We can use this to determine their distance.
O B A F G K M
(Hottest) (Coolest)
Also each spectral class is divided into 10: Sun à G2
23. Describe how a Hertzsprung–Russell diagram is constructed and used to identify stellar properties.
The HR diagram is a plot of the luminosity (or magnitude) of a star versus its temperature (or spectral class). From the diagram we can determine a star’s mass, temperature, luminosity, spectral class, and life expectancy.
24. Explain how the age of a star cluster can be determined using the HR diagram.
We can measure the age of a star cluster by finding the main sequence turn off point. Its age is equal to the hydrogen burning lifetime of the hottest, most luminous stars that remain.