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University of Wisconsin - Madison
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Universe: The Solar System w/Starry Night Enthusiast CD-ROM
The Earth differs from the Gas giants because
it is closer to the sun, has a higher percentage of heavier elements, and is less massive
Extra solar planets
Planets orbiting stars other than the sun
How can we know the sun is fueled by nuclear energy?
Because gravitational contraction wouldn't last long enough as an energy source
Why does the sun appear to be brighter than other stars?
It is much nearer than other stars
Which property of a star would not change if we could observe it from twice as far away?
Two stars have the same surface temp, but one has a radius 100 times that of the other. The luminosity of the larger star is:
ten thousand times greater
A cool star that is very luminous must have:
a large radius
How do we determine the temperature of a star in order to place it on the H-R diagram?
The temp is related to the peak wavelength emitted by the star which we measure from the star's spectrum
How do we measure the stars' Luminosity?
We can measure the brightness of the star and get the luminosity by measuring the distance. We can also measure the radius and the temp and get the luminosity by combining them.
Most of the brightest stars in the sky are:
giant stars and relatively hot main sequence stars
If we know that a group of stars are at the same distance, we can plot ___ in place of Luminosity and Temp on the H-R diagram
brightness and color
If 2 stars are on the main sequence, and one is more luminous than the other, we can be sure that the:
more luminous star is more massive.
How do we know that stars spend most of their lives on the main sequence?
We see more stars on the main sequence than anywhere else
What determines when a star becomes a main sequence star?
When nuclear fusion generates the energy required to balance gravity
What would happen if the temp in the core of the sun increased?
The rate of nuclear reactions in the core would increase, the radiation pressure would increase, the core would expand, and the temp in the core would eventually decrease
Why doesn't fusion occur in the corona?
The density in the corona is too low
In an H-R diagram plotting brightness in the visible and brightness in the infrared, what kinds of stars are we seeing?
Stars of the same age.
What does the mass of the Main Sequence Turn-off tell us?
The age of the cluster
Why do stars pass quickly along the HR diagram as they reach the Planetary Nebula phase?
High velocity gas cools quickly, changing the color of the star quickly
What is the primary source of energy for a white dwarf?
stored heat, cooling passively
When does a massive star form metals heavier than iron?
During a supernova
What would supernovae look like if there were no elements heavier than iron?
About the same as supernovae occurring due to core collapse, only with elements as heavy as iron in the core
How many times more luminous is a star with the same radius as the sun but twice as hot?
What is the basic evolutionary sequence of a star like the sun?
protostar, main sequence, red giant, planetary nebula, white dwarf
How does a white dwarf generate energy?
When does a supernova occur?
The core of a massive star collapses in an attempt to ignite iron
How do red giants get their name?
They are very large in diameter and very cool
What is the relationship between mass and luminosity of stars on the main sequence?
The greater the stellar mass, the larger the luminosity
What is the sun's predicted main sequence lifetime?
About 10 billion years, roughly half of which is over
If we know the true luminosity of a star and measure the flux from it, what can we determine?
Compared to main sequence stars of the same surface temperature, supergiants:
are more luminous, are less dense, and have larger radii
Two stars that have the same surface temperature have the same:
What fundamental property of a star determines its location on the main sequence?
How were elements heavier than iron originally produced?
Given five stars with the colors below, which has the lowest surface temperature?
Why do sunspots appear dark?
They are a bit cooler and thus dimmer than the rest of the photosphere.
What are blackbodies?
Bodies that absorb all energy of all wavelengths.
How do we know the age of the solar system?
We can measure the relative abundance of isotopes in rocks and use the half-life of the elements to determine the age.
If two blackbodies of the same temperature are different sizes, how different is their flux?
The flux is the same
What does the Oort Cloud do?
It sends comets into the solar system
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