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How are wavelength, frequency, and energy related for photons of light?
Longer wavelength means lower frequency and lower energy.
What is the approximate composition of the interstellar medium (by mass) in our region of the Milky Way?
70% hydrogen, 28% helium, 2% heavier elements
Photons behave like
both waves and particles
What eventually halts the gravitational collapse of an interstellar gas cloud that forms a brown dwarf rather than a true (main-sequence) star?
Degeneracy pressure caused by the high density of electrons in the core
Which has a greater mass: four protons or a helium nucleus with two protons and two neutrons?
four protons
Which of the following must be occurring in order for a molecular cloud to collapse and form stars?
The inward pull of gravity must be stronger than the outward push of thermal pressure.
A spaceship is moving past us at a speed close to the speed of light. What would we conclude about time (clocks) on the spaceship as it goes by?
We would conclude that their clocks are going slower than ours.
When an electron in an atom goes from a higher energy level to a lower energy level, the atom may
emit a photon of a specific wavelength.
Which of the following best describes the sizes of atoms?
Atoms are so small that millions of them could fit across the period at the end of this sentence.
Which of the following statements about an open star cluster is true?
All stars in the cluster are approximately the same age.
Which of the following properties of stars is directly observed (i.e., it can be measured by a calibrated instrument on a telescope, from a single observation without a need for additional calculations
apparent brightness
How does the Sun generate energy today?
nuclear fusion
Why isn't the Sun shrinking or expanding at present?
because gas pressure balances gravity in the Sun
The strength of gravity within a molecular cloud depends on
density only
A star's spectral type can be used to determine its
surface temperature.
Which of the following is the overall fusion reaction by which the Sun currently produces energy?
4 H —> 1 He + energy
Why do disks form around young stars?
Collisions between gas particles flatten the rotating gas cloud.
From lowest energy to highest energy, which of the following correctly orders the different regions of electromagnetic radiation?
radio, infrared, visible light, ultraviolet, x-rays, gamma rays
What are the standard units for apparent brightness?
watts per square meter
According to measurements made here on Earth, the distance to Alpha Centauri is about
4 light-years. If a spaceship is traveling toward Alpha Centauri at 0.999c, How far away is Alpha
Centauri according to the travelers in the ship?
quite a bit less than 4 light-years
The predictions of special relativity can sound implausible at first. Which of the following provide
observational evidence that the theory is correct?
all of the above are correct
Bob is coming toward you at a speed of 75 km/hr. You throw a baseball in his direction at 75 km/hr.
What does he see the ball doing?
He sees the ball coming at him at 150 km/hr.
On a Hertzsprung-Russell diagram, where would we find stars that are cool and dim?
lower right
How do we measure stellar masses?
We measure the orbital periods and velocities of stars in binary systems.
Sue is traveling toward you at 90 km/hr. She throws a baseball that, according to her, is going at 90
km/hr in the opposite direction. What do you see the ball doing?
you see the ball remaining stationary
Which of the following stars has the hottest surface temperature?
blue star
Why do sunspots appear dark?
They are regions that are significantly cooler than the rest of the photosphere.
What is the approximate average temperature of the surface of the Sun?
5800 K
If you see Alice going to your left at exactly 0.99c and Bob going to your right (away from Alice) at
exactly 0.99c, what will Alice say Bob is doing?
going away from her faster than 0.99c, but slower than c
Which of the following people reorganized the spectral classification scheme into the one we use
today and personally classified over 400,000 stars?
Annie Jump Cannon
) Approximately how long does the protostellar stage last for a starlike our Sun?
30 million years
what is a molecule
a group of two or more atoms bound together
where do stars form and why
Stars form in cold gas clouds because gravity has to be stronger than gas pressure
Carol is going away from you at 75 km/hr, and Sam is going in the opposite direction away from
you at 90 km/hr. According to Carol, how fast is Sam going?
Carol sees Sam going away from her at 165 km/hr.
What two forces are balanced in what we call gravitational equilibrium?
outward pressure and inward gravity
why cant we see radio waves
Radio waves have wavelengths too long for the eye to detect.
Which of the following best explains why nuclear fusion requires bringing nuclei extremely close
together?
Nuclei normally repel because they are all positively charged and can be made to stick only when brought close enough for the strong force to take hold.
What is thought to prevent the formation of stars with masses larger than about 300 times that of
our Sun?
Such massive stars would generate so much light that radiation pressure would blow them
apart
What keeps the Sun's outer layers from continuing to fall inward in a gravitational collapse?
outward pressure due to hot gas
The youngest star clusters are ones in which their brightest main-sequence stars have spectral type
O
in a pulsating variable star, which characteristic of the star changes dramatically with time?
luminosity
Which two things are the same for all observers according to the theory of relativity?
(1) the laws of nature and (2) the speed of light
Which of the following statements about the sunspot cycle is not true?
The rate of nuclear fusion in the Sun peaks about every 11 years.
if a material is transparent, then it
transmits light well
the most fundamental property of a star is its
mass
grass can appear green because it
it reflects green light and absorbs other colors.
In general, the time it takes from when in interstellar cloud fragment first begins collapsing until it
gives birth to a main-sequence star is
longer for less massive stars.
What is the primary source of energy for protostars (that have not yet become hot enough for
fusion in their cores)?
gravitational contraction
A spaceship is moving past us at a speed close to the speed of light. If we could measure the mass
of the spaceship as it goes by, what would it be?
its mass is greater than its rest mass
Al is moving by you at a very high speed (close to the speed of light). You get out a clock and
measure 10 seconds going by. If you also watch a clock in Al's ship, how much time will you see it
record during your 10 seconds?
You will see Al's clock record less than 10 seconds
