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%\fancyfoot[LE,RO]{Ralf Kotulla}
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%% %\fancyhead[C]{Ralf Kotulla: Modeling explosive transient populations}
%% \fancyhead[L]{Scientific Data Processing \& Visualization in the cloud}
%% \fancyhead[R]{Ralf Kotulla: CIF21 DIBBs}














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\fancyhead[L]{Astronomy 103 - Midterm 2}
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\begin{document}
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\begin{center}
\large\bf Astronomy 103 --  Midterm 2 --  October 29, 2014
\end{center}


%\bigskip
%{\bf Solutions: correct answers are marked in bold, red type.}

\bigskip
{\bf Instructions:  } 

{\bf No books, notes or calculator are allowed.} You have 50 minutes to complete the exam, and please do not turn to the next page until instructed to do so.

%% {This exam consists of 50 questions. 45 correct questions correspond to a
%%   score of 100\%, i.e. 5 out of the 50 questions are bonus questions}

\bigskip
{\bf You may find the following information helpful:}

\begin{itemize}
\item{1 AU $=3\times10^8$ km}

\item{speed of light $c=3\times10^5$ km/s}

\item{Kepler's 3rd law: 
\[
a^3 = P^2 
\]
with the period $P$ in years and semi-major axis $a$ in AU.}

\item{Newton's law of gravity:
\[
F = \frac{GMm}{r^2}
\]}

\item{Peak wavelength and temperature of blackbody radiation:
\[
\lambda = \frac{3\times10^6}{T} \mbox{ nm}
\]
with wavelength $\lambda$ in nm (1 nm = $10^{-9}$ m) and temperature $T$ in
Kelvin.}

\item{Relationship between frequency $f$ and wavelength $\lambda$ of light:
\[
\lambda = \frac{c}{f}
\]}

\item{Conversion of mass into energy:  $E=mc^2$}

\item{Relationship between brightness $B$ and distance $d$:
\[
B_2 = B_1 \times \frac{d_1^2}{d_2^2}
\]}

\item{Relationship between luminosity $L$, temperature $T$ and radius $R$ of stars: 
\[
L=4\pi\sigma T^4 R^2
\]
where $4\pi \sigma$ are constants.}

\end{itemize}
\newpage

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\begin{enumerate}[label=\arabic*.~, leftmargin=2em, itemsep=3ex]


\item Light of which of the following kinds is observed by earthbound
  telescopes? 
\begin{enumerate} 
\correctitem{ radio waves and visible light}
\item x-rays and gamma rays 
\item gamma rays and radio waves 
\item visible light and x-rays
\end{enumerate}





\item The main advantage of the Hubble Space Telescope compared to telescopes on Earth is:

\begin{enumerate} 
\item friendly aliens help out when it has problems 
\correctitem{ it avoids atmospheric turbulence }
\item it can detect radio waves 
\item it can detect sound waves that do not reach the Earth
\end{enumerate}





\item Radio telescopes are large in part to improve their resolution, which is poor because of the long wavelengths at which they are used to observe the skies.

\begin{enumerate} 
\correctitem{ True}
\item False
\end{enumerate}



\item Why are satellites used to detect x-rays?

\begin{enumerate} 
\item space-based detectors are more sensitive 
\item they avoid atmospheric turbulence 
\correctitem{ x-rays are absorbed by the Earth's atmosphere }
\item to avoid interference from x-ray sources on Earth
\end{enumerate}




\item A gamma-ray telescope has the same design as a telescope used to observe visible light.
\begin{enumerate} 
\item True 
\correctitem{ False}
\end{enumerate}


% RK bonus
\item The Herschel Infrared Space Telescope is stationed far from earth because
\begin{enumerate}
\item This increases the telescope's field of view
\item The telescope is sensitive to electromagnetic interference from
  terrestrial radio stations
\item Doing so avoids the obscuring effects of dust close to the ground.
\correctitem{ Earth is a heat source and the telescope must be kept very cold.}
\end{enumerate}



\newpage
\item Sunspots appear dark because they are hotter than the surrounding gas of the photosphere.

\begin{enumerate} 
\item True 
\correctitem{ False}
\end{enumerate}




\item About how hot is the Sun's photosphere?
\begin{enumerate} 
\item 3K 
\item 300 K 
\item 3000 K 
\correctitem{ 6000 K }
\item 10,000 K
\end{enumerate}





\item The visible light we see from the Sun comes from what part of the Sun?
\begin{enumerate} 
\correctitem{ photosphere }
\item corona 
\item chromosphere 
\item core
\end{enumerate}




% RK bonus

\item The sun rotates
\begin{enumerate}
\correctitem{ fastest near the equator }
\item fastest near the poles
\item with the same speed at all latitudes
\item not at all.
\end{enumerate}



\item What is the most abundant element in the Sun?
\begin{enumerate} 
\correctitem{ hydrogen}
\item helium
\item carbon
\item oxygen
\item iron
\end{enumerate}




\item The Sun is a stable star in which

\begin{enumerate} 
\item the rate of fusion equals the rate of fission 
\item the rate at which energy is emitted by the core is equal to the rate at
which energy is absorbed in the corona
\item radiation and convection balance one another
\correctitem{ gravity balances the force from pressure}
\end{enumerate}






\item How many times more massive is the Sun than the Earth?
\begin{enumerate} 
\item 100
\correctitem{ 300,000}
\item 100 million
\end{enumerate}




\item The Sun's energy is produced by the fusion of
\begin{enumerate} 
\item hydrogen and oxygen to water
\item carbon to iron
\item helium to carbon
\item oxygen to iron
\correctitem{ hydrogen to helium}
\end{enumerate}




\item The density of the Sun is closest to that of which of the objects listed below?
\begin{enumerate} 
\correctitem{ an ice cube}
\item the Earth
\item an asteroid
\item the Earth's atmosphere
\end{enumerate}






\item Compared to the Sun's corona, its photosphere is
\begin{enumerate} 
\item denser and hotter
\correctitem{ denser and cooler}
\item less dense and hotter
\item less dense and cooler
\end{enumerate}



\item When hydrogen fuses to helium, what fraction of its mass changes to energy?
\begin{enumerate} 
\item 100\%
\item 70\%
\item 50\%
\item 5\%
\correctitem{ 0.7\%}
\end{enumerate}







\enlargethispage{2em}
\item If 10 kg of mass is changed entirely into energy, how much energy is produced?
\begin{enumerate} 
\item 10 watt-seconds
\item 3 x 10$^{8}$ watt-seconds
\item 3 x 10$^{16}$ watt-seconds
\item 9 x 10$^{16}$ watt-seconds
\correctitem{ 9 x 10$^{17}$ watt-seconds}
\end{enumerate}


\item If the luminosity of a star is 9.0 $\times$ 10$^{26}$ watts, how much mass does it change to energy each second?
\begin{enumerate} 
\item 3 x 10$^{8}$ kg
\correctitem{ 1 x 10$^{10}$ kg}
\item 9 x 10$^{10}$ kg
\item 3 x 10$^{18}$ kg
\item 9 x 10$^{18}$ kg
\end{enumerate}




\item Which of the following lists gives the spectral types of stars in order from the type corresponding to stars with the hottest surfaces to the type corresponding to stars with the coolest surfaces?
\begin{enumerate} 
\item F, B, G, O, M 
\item A, B, F, G, O 
\correctitem{ O, B, F, G, M }
\item K, M, F, G, B 
\item B, G, F, M, K
\end{enumerate}




\item Star A appears brighter than star B, as seen from Earth. Therefore, start A must be closer to Earth than star B.
\begin{enumerate} 
\item True
\correctitem{ False}
\end{enumerate}



\item Stars with cool surfaces can be very luminous if they are very
\begin{enumerate} 
\item small
\item hot
\correctitem{ large}
\item close to our solar system
\end{enumerate}







\item Which two of the following need to be measured in order to determine the luminosity of a star?
\begin{enumerate} 
\item apparent brightness and temperature
\item temperature and mass
\correctitem{ distance and apparent brightness}
\item mass and distance
\end{enumerate}



\newpage
\item Once the luminosity of a star is known, what has to be measured in order to find the star's radius?
\begin{enumerate} 
\item parallax angle to find distance
\item color to find distance
\correctitem{ color to find surface temperature }
\item parallax angle to find surface temperature
\end{enumerate}






\item About what fraction of stars are in binary systems?
\begin{enumerate} 
\item 1/10
\correctitem{ 1/2}
\item 9/10
\end{enumerate}




\item What two physical characteristics of stars are related by an H-R diagram?
\begin{enumerate} 
\item mass and luminosity
\correctitem{ luminosity and surface temperature}
\item mass and surface temperature
\item mass and radius
\item luminosity and radius
\end{enumerate}




\item About what fraction of stars are on the main sequence?
\begin{enumerate} 
\item less than 10\%
\item about 50\%
\correctitem{ about 90\%}
\end{enumerate}





\item If the Sun had a cooler surface, it would be
\begin{enumerate} 
\item bluer
\correctitem{ redder}
\item there would be no difference in its color
\end{enumerate}




\item From a distance of 1 parsec, the angular size (radius) of Earth's orbit would be
\begin{enumerate} 
\correctitem{ 1 arc second}
\item 1 degree
\item 2 degrees
\item impossible to determine
\end{enumerate}




\item The planets Londinium and Bellerophon orbit a star called the White Sun. Londinium is 1 AU from the star, and Bellerophon is 10 AU away. The brightness of light from the White Sun on Londinium is about 100 watt/meter$^2$. What is the brightness of light from the White Sun on Bellerophon?

\begin{enumerate} 
\correctitem{ 1 watt/meter$^2$}
\item 10 watt/meter$^2$
\item 1000 watt/meter$^2$
\item 10,000 watt/meter$^2$
\end{enumerate}




\item Compared to a main-sequence star of type G, a main-sequence star of type B is:
\begin{enumerate} 
\item hotter and less massive
\correctitem{ hotter and more massive}
\item cooler and less massive
\item cooler and more massive
\end{enumerate}







\item Stars of spectral class M do not show strong lines of hydrogen in their spectra because
\begin{enumerate} 
\item they contain very little hydrogen 
\correctitem{ their surfaces are so cool that most hydrogen is in the ground state}
\item their surfaces are so hot that most hydrogen is ionized elements
\item the hydrogen lines are swamped by even stronger lines of other elements
\end{enumerate}




\item What type of star is the Sun?
\begin{enumerate} 
\item A 
\item B
\item F
\correctitem{ G}
\item O
\end{enumerate}


%% RK BONUS
\item You observe two stars in the sky. Star A is a spectral class O supergiant,
  star B is a spectral class O white dwarf. What can you say about their
  temperatures?
\begin{enumerate} 
\item A is hotter than B
\item B is hotter than A
\correctitem{ A and B have approximately the same temperature}
\item We do not have enough information to derive their temperatures.
\end{enumerate}


\newpage
\item When visible light from a star passes through interstellar dust, the light
\begin{enumerate} 
\item ionizes the dust, which then emits blue and ultraviolet light
\item is dimmed and becomes bluer
\correctitem{ is dimmed and reddened}
\item primarily excites electrons in the silicon atoms of the dust. We observe
ultraviolet light when the electrons fall back to their ground state.
\item is Doppler shifted
\end{enumerate}




\item Two clouds of interstellar gas contract to form stars. Suppose that no mass is lost in the contraction and that when they stop contracting, cloud A is a type A star and cloud K is a type K star. Compared to cloud A, cloud K has
\begin{enumerate} 
\item the same mass and the same percentage of hydrogen
\item a smaller percentage of hydrogen
\item a larger percentage of hydrogen
\item more mass
\correctitem{ less mass}
\end{enumerate}




\item Two clouds of interstellar gas contract to form stars. Suppose that no
  mass is lost in the contraction and that when they stop contracting, cloud A
  is a type A star and cloud K is a type K star. What stops the contraction of
  each star?
\begin{enumerate} 
\item Cloud A is stopped by fusion of helium to carbon and cloud K is stopped
by fusion of hydrogen to helium
\item Cloud K is stopped by fusion of helium to carbon and cloud A is stopped 
by fusion of hydrogen to helium
\correctitem{ Both clouds are stopped by fusion of hydrogen to helium }
\item Both clouds are stopped by fusion of helium to carbon 
\item None of these answers is even remotely related to what happens in the
formation of stars. 
\end{enumerate}




\item A main-sequence star with a mass of 15 times the mass of the Sun has a lifetime that is
\begin{enumerate} 
\item much longer than the Sun's.
\correctitem{ much shorter than the Sun's.}
\item about the same as the Sun's.
\end{enumerate}


\item It takes less and less time to fuse heavier and heavier elements inside a highmass star.
\begin{enumerate} 
\correctitem{ True}
\item  False
\end{enumerate}




% RK bonus
\item Star formation requires a sufficient amount of $\ldots\ldots\ldots$ to begin.
\begin{enumerate}
\item Hot gas with millions of degrees K
\correctitem{ Cold gas with temperatures of tens of degrees K}
\item Asteroid collisions
\item Emission from emission nebulae
\item Ionizing radiation
\end{enumerate}



\item What is the next stage in the Sun's evolution?
\begin{enumerate} 
\item neutron star
\item T-Tauri star
\item white dwarf
\item type F main-sequence star
\correctitem{ red giant}
\end{enumerate}




\item Most of the nitrogen on Earth was
\begin{enumerate} 
\item formed in a supernova
\correctitem{ formed in a star that later exploded in a supernova }
\item formed in a planetary nebula 
\item formed in a star that then lost its outer envelope in a planetary nebula
\end{enumerate}






\item In a core-collapse supernova, the outer part of the core rebounds from the inner, high-density core, destroying the entire outer part of the star.
\begin{enumerate} 
\correctitem{ True}
\item False
\end{enumerate}






\item  A nova is a sudden outburst of light coming from an old main sequence star.
\begin{enumerate} 
\item True
\correctitem{ False}
\end{enumerate}





\item One billion years from now the Sun will be a
\begin{enumerate} 
\item red giant
\correctitem{ main-sequence star}
\item white dwarf
\item none of the above
\end{enumerate}






\newpage
\item Match the phases of stellar evolution listed below (1-4) to the
  appropriate energy generating processes (A-D). 

\begin{enumerate}[label=\arabic*]
\item Contraction of the core and fusion of hydrogen to helium in a shell 
\item Fusion of helium to carbon in the core 
\item Contraction of the entire star 
\item Fusion of hydrogen to helium in the core 
\end{enumerate}

\begin{enumerate}[label=\Alph*]
\item The energy source for a star just after the helium flash. 
\item The energy source of a star in its first red-giant stage. 
\item The energy source of a main sequence star. 
\item The energy source of a protostar, before it has reached the main sequence.
\end{enumerate}

\begin{enumerate}
\item 1 and B, 2 and D, 3 and C, 4 and A 
\item 1 and A, 2 and B, 3 and D, 4 and C 
\item 1 and D, 2 and A, 3 and C, 4 and B 
\item 1 and C, 2 and B, 3 and A, 4 and D 
\correctitem{ 1 and B, 2 and A, 3 and D, 4 and C }
\end{enumerate}






\item Put the following stages in a star's evolution in chronological order from first to last:

\begin{enumerate}[label=\Alph*]
\item contraction of a gas cloud 
\item main-sequence star 
\item ejection of a planetary nebula 
\item first red giant stage 
\item fusion of helium to carbon in the core
\end{enumerate}

\begin{enumerate} 
\item C, A, B, E, D 
\item A, D, B, E, C 
\item B, A, C, E, D 
\correctitem{ A, B, D, E, C }
\item A, B, C, D, E
\end{enumerate}




\item What is the upper limit on the mass of a white dwarf?
\begin{enumerate} 
\item 0.08 solar masses
\item 0.5 solar masses
\correctitem{ 1.4 solar masses}
\item 10 solar masses
\end{enumerate}





\newpage
\item Match the descriptions below to their names: 

\begin{enumerate}[label=\Alph*]
\item Type I supernova 
\item Nova 
\item Planetary nebula 
\item Type II supernova
\end{enumerate}

\begin{enumerate}[label=\arabic*]
\item The ejected outer part of a star whose core becomes a white dwarf. 
\item The explosion that results from hydrogen from a companion star falling
  onto a white dwarf and suddenly fusing to helium when it gets hot enough to
  ignite. 
\item The explosion that results from the gravitational collapse of the iron
  core of a massive star when it approaches its upper mass limit. 
\item The explosion that results from the gravitational collapse of a white
  dwarf when it approaches or reaches its upper mass limit. 
\end{enumerate}

\begin{enumerate}
\correctitem{ 1 and C, 2 and B, 3 and D, 4 and A }
\item 1 and A, 2 and B, 3 and D, 4 and C 
\item 1 and D, 2 and A, 3 and C, 4 and B 
\item 1 and C, 2 and B, 3 and A, 4 and D 
\item 1 and B, 2 and A, 3 and D, 4 and C
\end{enumerate}










% rk BONUS
\item What ages does a star cluster have in which all stars have masses similar to or less than the
  mass of our Sun?
\begin{enumerate}
  \correctitem{ A large age of many billions of years}
  \item A very young age of at most a few millions of years
  \item Each star has a different age, so we can not tell the age of the cluster
\end{enumerate}

\end{enumerate}

\label{lastpage}

\end{document}
