Exam II Material Flashcards
Cluster ages can be determined from:
a) main sequence fitting
b) main sequence turnoff
c) pulsating variable stars
d) spectroscopic binaries
e) visual binaries
b) main sequence turnoff
Hydrogen fusion in the Sun requires a temperature (in Kelvin) of:
a) thousands of degrees
b) millions of degrees
c) billions of degrees
d) trillions of degrees
e) any temperature, as long as gravity is strong enough
b) millions of degrees
In the late 1800s, Kelvin and Helmholtz suggested that the Sun stayed hot thanks to gravitational contraction. What was the major drawback of this idea?
a) it predicted that the Sun could last only about 25 million years, which is far less than the age of Earth
b) it predicted that the Sun would shrink noticeably as we watched it, and the Sun appears to be stable in size
c) it is physically impossible to generate heat simply by making a star shrink in size
d) it predicted that Earth would also shrink, which would make it impossible to have stable geology on our planet
e) it was proposed before Einstein’s theory of general relativity and was therefore incorrect
a) it predicted that the Sun could last only about 25 million years, which is far less than the age of Earth
What two forces are balanced in what we call gravitational equilibrium?
a) the electromagnetic force and gravity
b) outward pressure and the strong force
c) outward pressure and gravity
d) the strong force and gravity
e) the strong force and kinetic energy
c) outward pressure and gravity
When is/was gravitational contraction an important energy-generation mechanism for the Sun?
a) only during solar minimum
b) only during solar maximum
c) when the Sun was being formed from a collapsing cloud of gas
d) right after the Sun began fusing hydrogen in its core
e) when the Sun transports radiation through the convection zone
c) 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?
a) the hydrogen gas in the Sun is balanced so that it never rises upward or falls downward
b) the Sun maintains a steady temperature
c) this is another way of stating that the Sun generates energy by nuclear fusion
d) there is a balance within the Sun between the outward push of pressure and the inward pull of gravity
e) the Sun always has the same amount of mass, creating the same gravitational force
d) there is a balance within the Sun between the outward push of pressure and the inward pull of gravity
How does the Sun generate energy today?
a) nuclear fission
b) nuclear fusion
c) chemical reactions
d) gravitational contraction
e) gradually expanding in size
b) nuclear fusion
At approximately what temperature can helium fusion occur?
a) 100,000 K
b) 1 million K
c) a few million K
d) 100 million K
e) 100 billion K
d) 100 million K
White dwarfs are so called because:
a) they are both very hot and very small
b) they are the end-products of small, low-mass stars
c) they are the opposite of black holes
d) it amplifies the contrast with red giants
e) they are supported by electron degeneracy pressure
a) they are both very hot and very small
A teaspoonful of white dwarf material on Earth would weigh:
a) the same as a teaspoonful of Earth-like material
b) about the same as Mt. Everest
c) about the same as Earth
d) a few tons
e) a few million tons
d) a few tons
Which of the following is closest in mass to a white dwarf?
a) the Moon
b) Earth
c) Jupiter
d) Neptune
e) the Sun
e) the Sun
If you were to come back to our Solar System in 6 billion years, what might you expect to find?
a) a red giant star
b) a white dwarf
c) a rapidly spinning pulsar
d) a black hole
e) Everything will be pretty much the same as it is now
b) a white dwarf
Why are Cepheid variables important?
a) Cepheid variables are stars that vary in brightness because they harbor a black hole
b) Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as “standard candles” for distance measurements
c) Cepheids are a type of young galaxy that helps us understand how galaxies form
d) Cepheids are supermassive stars that are on the verge of becoming supernovae and therefore allow us to choose candidates to watch if we hope to observe a supernova in the near future
b) Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as “standard candles” for distance measurements
What is a standard candle?
a) an object for which we are likely to know the true luminosity
b) an object for which we can easily measure the apparent brightness
c) a class of objects in astronomy that all have exactly the same luminosity
d) any star for which we know the exact apparent brightness
e) a long, tapered candle that lights easily
a) an object for which we are likely to know the true luminosity
Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ?
a) location where they are formed
b) time they are formed
c) luminosity they are formed with
d) mass they are formed with
e) color they are formed with
d) mass they are formed with
