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Homework Help: Push me in the right direction

  1. Aug 3, 2006 #1
    Here's my astronomy homework for the week.
    bold = my answer.
    Any help is appreciated!!

    Question 1 Multiple Choice 5 points
    The apparent brightness of stars in general tells us nothing about their distances. In order for the aparent brightness of a star to be a good indicator of its distance, all the stars would have to be:
    at the same distance
    the same composition
    the same luminosity
    by themselves instead of binary or double-star systems

    Question 2 Multiple Choice 5 points
    Whic if the following stars is a Cepheid variable?

    Question 3 Multiple Choice 5 points
    Astronomers must often know the distance to a star before thay can fully understand its characteristics. Which of the following properties of a star typically requires a knowledge of distance before it can be determined?
    its luminosity
    its radial velocity
    its temperature
    its apparent brightness

    Question 4 Multiple Choice 5 points
    Which of the following will show the smallest parallax shift?
    the Moon
    the planet Jupiter
    the Sun
    the star 51 Pegasi, about 50 LY away

    Question 5 Multiple Choice 5 points
    You are observing a binary star system and obtain a series of spectra of the light from the two stars. In this spectrum, most of the absorption lines shift back and forth as expected from the Doppler effect. A few lines, however, do not shift at all, but remain at the same wavelength. How can we explain the behavior of the non-shiftnig lines?
    there is a star in the system which is not moving at all: it is just sitting there
    there is a planet orbiting the stars in the system
    there are huge clouds of dust just behind this star system from our perspective
    the lines come from interstellar matter between us and the star, not from the stars themselves

    Question 6 Multiple Choice 5 points
    An astronomer wants to observe a cloud of cold neutral (not ionized) hydrogen, far away from any stars. What would be an instrument that could help in this task?
    a telescope in space, able to pick up x-rays from space
    a radio telescope , tuned to a wavelength of about 21 cm
    a large telescope observin visible light, but with a very sensitive detector attached
    a neutrino detector, deep underground

    Question 7 Multiple Choice 5 points
    Astronomers have found large quantities of cold, neutral hydrogen gas in our galaxy. How is this gas distributed?
    it is located only near stars, and not in the large empty spaces between them
    it is found mostly in a flat layer extending throughout the disk of our galaxy
    it is found in a spherical distribution about 100 LY in size, cenetered on the Sun
    if is found only in the outer regions of the galaxy, where we are, and not in the central areas.

    Question 8 Multiple Choice 5 points
    Observations show that some gas in interstellar space has been heated to temperature of a million degrees or so. What mechanism do astronomers believe is reponsible for this heating?
    Stars like the sun shine on the gas, heating it
    Th eatoms in the gas collide, heating each other
    new stars are forming in the regions of hot gas, heating it
    exploding stars are responsible for heating the gas with the energy of their explosion.

    Question 9 Multiple Choice 5 points
    A star whose temperature is increasing but whose luminosity is roughly constant moves in what direction on the H-R diagram?
    to the right
    to the left

    Question 10 Multiple Choice 5 points
    Astronomers identify the "birth" of a real star (as opposed to the activities of a protostar) with what activity in the star?
    when it starts to contract rapidly from a cloud of gas and dust
    when it first becomes visible inside its dust cloud
    when a wind is observed coming from its surface
    when nuclear fusion reactions begin inside its core

    Question 11 Multiple Choice 5 points
    The big surprise about the first planet discovered around another (liing) star was that it
    was smaller than Mercury or Pluto in our own solar system
    orbited so close too its star it took only 4 days to go around
    has a mass greater than that of most stars
    had a spectrum which indicated it was made of elements we never find on Earth

    Question 12 Multiple Choice 5 points
    With the technique used to discover the first planets around other living stars, only some kinds of planets can be found. The kinds of planets we are able to find with this technique today are:
    only terrestrial planets
    only cold planets
    only planets that have masses like Jupiter or Saturn
    only planets with giant orbits (like Pluto or larger)

    Question 13 Multiple Choice 5 points
    Which of the following types of stars will spend the longest time (the greatest number of years) on the main sequence?

    Question 14 Multiple Choice 5 points
    How long a main sequence star remains on the main sequence in the H-R diagram depends most strongly on
    its initial composition
    the number of companion stars or planets orbiting it
    its radial velocity
    its mass

    Question 15 Multiple Choice 5 points
    When the outer layers of a star like the Sun expand, and it becomes a qiant, which way does it move on the H-R diagram?
    toward the upper right
    toward the upper left
    toward the lower right
    toward the lower left

    Question 16 Multiple Choice 5 points
    A star with a mass like the sun which will soon die is observed to be surrounded by a large amount of dust and gas - all material it has expelled in the late stages if uts life. if asrtonomers want to observe the radiation from such a giant star surrounded by its own debris, which of the following bands of the spectrum would be the best to use ot observe it?

    Question 17 Multiple Choice 5 points
    The event in the life of a star that begins its expansion into a giant is
    the core reaches a temperature of ten million degrees
    as much as 90% of the star explodes violently
    almost all the hydrogen in its core that was hot enough for fusion has been turned into helium the star's internal structure reaches equilibrium for the first time in its life

    Question 18 Multiple Choice 5 points
    A white dwarf, compared to a main sequence star with the same mass, would always be:
    redder in color
    smaller in diameter
    the same size
    younger in age

    Question 19 Multiple Choice 5 points
    A neutron star as as dence as
    the center of the Earth
    a white dwarf star
    the nucleus of an atom

    Question 20 Multiple Choice 5 points
    Astronomers have concluded that pulsars are
    rotating black holes
    rotating neutron stars
    rotating red giants
    supernovae that are about to explode
  2. jcsd
  3. Aug 3, 2006 #2


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    4 is wrong. Do you know what parallax is?
    12 is wrong. This should have been obvious to you, since you got 11 right.
    Last edited: Aug 3, 2006
  4. Aug 3, 2006 #3
    Also, euph, if you're not sure about number one, pick d.
  5. Aug 4, 2006 #4
    So what is parallax? i don't know too.
  6. Aug 4, 2006 #5
    not really sure what parallax is. As for #12, is it only planets that have masses like Jupiter or Saturn? Is #1 D? I got confused
  7. Aug 4, 2006 #6


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    How about changing #13 to K.?
    #16 is wrong too.
  8. Aug 4, 2006 #7

    No, he was right.
  9. Aug 4, 2006 #8


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    Staff: Mentor

    Hold your hand out at arms' length and cover a distant object with it while closing one eye. Then open the other eye. Now you can see the distant object. That's parallax (the parallax of your hand wrt a fixed background).
  10. Aug 4, 2006 #9
    thanks for everyone's help so far, or lack thereof
  11. Aug 7, 2006 #10


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    Right. Now. Your hand is about two feet away from your eye. If it were two hundred feet away, would you get more or less parallax?
    OK, now, what will show only a little parallax -the Moon only 300,000km away or a star light years away?
  12. Aug 8, 2006 #11


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    same distance.



    51 Pegasi. More distant = less parallax.


    a radio telescope tuned to 21 cm - you can only detect absorption lines in a neutral hydrogen cloud, which is at 21 cm.


    Exploding stars. Radiation from ordinary stars will not be energetic enough to heat interstellar gas clouds to these temperatures.




    Only massive planets.

    K. OBAFGKM - Oh Be A Fine Girl Kiss Me [Quick Right Now]. K stars start out less massive than G stars hence remain longer on the main sequence.



    Infrared. A star like the sun will become a red giant and emit most strongly in the red wavelengths.



    Last edited: Aug 8, 2006
  13. Aug 8, 2006 #12


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    Higher temperatures are on the left side of the HR Diagram.

    And I find it stunning you got most of the answers right and you don't know what parallax is! That is some kind of astronomy course you are taking.
  14. Aug 8, 2006 #13
    yeah to be honest I still dont understand what all this arm's length parallax stuff is..
  15. Aug 8, 2006 #14
    Chronos, are you sure about that? I'm inclined to go with euphoria's initial answer: knowing the luminosity of a star and its apparent brightness gives you its distance from us. If all stars were to be equally luminous, their apparent brightnesses would indicate their different distances from us. I don't see how putting stars of different luminosity at the same distance from us would tell us how large that distance would be. I could be missing something, of course!
  16. Aug 8, 2006 #15


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    I was about to post the (approximate) same reply. Quite sure that you are correct on this one.
  17. Aug 8, 2006 #16
    #9 is to the left
    #5 is the last choice
    #1 is the answer I picked..
    even with everyone's help i still got 2 wrong
    but, thanks for everyones help
  18. Aug 8, 2006 #17
    more help needed

    hey guys.. this is my last homework and I want to make sure I do well and understand the material for the approaching final exam.

    Question 1 Multiple Choice 10 points
    The principle of equivalence says that
    the amount of energy released by fusion is equivalent to the amount of mass that is lost
    gravity is equivalent to the strong nyclear force inside of any nucleus
    the effects of gravity are equivalent to the effects of acceleration
    far away from a black hole, its pull is equivalent to the pull of the star that is formed from

    Question 2 Multiple Choice 10 points
    The region around a black hole where everything is trapped, and nothing can get out to the rest of the universe, is called
    the singularity
    the neutron star radius
    the gravitational redshift zone
    the event horizon

    Question 3 Multiple Choice 10 points
    Far away from a black hole (at the distance of another star), which of the following is a possible way to detect it?
    notice what a large amount of star light it blocks from behind it
    look for the pulsed radio waves it gives off as it rotates like a lighthouse
    look for the neutrinos that always escape from the event horizon
    search for flickering x-rays being given off as it "eats" part of a neighbor star.

    Question 4 Multiple Choice 10 points
    An astronomer needs to measure the distance to a globular cluster of stars that is part of the Milky Way Galaxy. What method should she try to use to find the distance?
    measure the parallax of the cluster
    count the number of O and B stars in the cluster
    look for flickering x-rays coming from a black hole in a binary star system in the cluster
    find a variable star (ceoheid or RR Lyrae) in the cluster

    Question 5 Multiple Choice 10 points
    Which of the following statements about the nuclear bulge of our Galaxy is FALSE?
    it is significantly thicker that the disk of the Galaxy
    typically consists of older stars
    it is difficult for us to see with visible light because of cosmic dust
    the best way to learn more about it is yo observe ligher energy radiation, such as UV and x-rays

    Question 6 Multiple Choice 10 points
    Where would you look for the youngest stars in the Milky Way Galaxy?
    in the halo
    where there is the dark matter
    in the disk
    in the nuclear bulge

    Question 7 Multiple Choice 10 points
    If I want to find a sizable collection of Population II stars in the Milky Way Galaxy, where would it be a good place to look?
    near the Sun
    in a globular cluster high above the Galaxy's disk
    in the Orion Spiral Arm
    on the outer surface of giant nolecular clouds

    Question 8 Multiple Choice 10 points
    Our Milky Way Galaxy is what type of galaxy?
    dwarf elliptical

    Question 9 Multiple Choice 10 points
    Which galaxy is observed to contain mostly older stars?
    dwarf elliptical

    Question 10 Multiple Choice 10 points
    Which type of Galaxy is very difficult to see but (astronomers recently relized) may be very common?
    dwarf elliptical
  19. Aug 8, 2006 #18


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    You might want to think more about #5, #7, and #10. What kind of light does dust obscure? What is a Population II star? What would make a galaxy difficult to see?
  20. Aug 9, 2006 #19


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    No, you are not missing anything, I had a dyslexic moment.
  21. Aug 9, 2006 #20


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    You have to do it to get it.

    1] Close one eye.
    2] Hold your thumb in front of your eye at arm's length - about two feet away.
    3] Move your thumb to hide something on the wall across the room, say a picture.
    4] Now, switch eyes: close one, open the other. Is the picture still hidden? It's off to the side a little bit, right?

    Now, do it again, but this time hold your thumb only 6" away:

    1] Close one eye.
    2] Hold your thumb in front of your eye about 6" away.
    3] Move your thumb to hide the picture.
    4] Switch eyes: close one, open the other. The picture, rather than being a little off to the side, is now waaay off to the side, right?

    The closer your thumb is to your eye, the more parallax shift (movement against the wall) is observed. If you knew nothing about your thumb except how much shift it exhibited, you could tell how far away it was from your eye.

    Now, scale it up.
    - The distance between your eyes is equiv. to the diameter of the Earth's orbit
    - Your thumb is a star of unknown distance
    - The wall is the background of stars (which is effectively at infinite distance, so no shift)

    By seeing how much parallax shift the star undergoes over six months of the Earth's orbit, you can estimate its distance from us.
    Last edited: Aug 9, 2006
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