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Tuesday, January 25

  1. page Q18Mock11 edited ... January 2011 Mock: Question 18 a) 4.6 days b) If (x distance from peak to peak) b) The re…
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    January 2011 Mock: Question 18
    a) 4.6 days
    b) If(x distance from peak to peak)
    b) The relationship between a Cepheid variable's period and its luminosity is almost directly proportional. So, if
    you know
    ...
    of a CephidCepheid variable star,
    ...
    the period-luminosity law.law (luminosity is essentially the same as absolute magnitude). Then, using
    ...
    in parsecs.
    Or: Where I=intensity of light observed from Earth, L = the star's luminosity and D = the distance to the star,
    I=L/4piD^2
    Rearranging this equation gives us:
    D=sqrt(L/4piI)

    c) The
    ...
    to the starstar.
    *Suitable diagram*
    (view changes)
    1:49 pm
  2. page Q17Mock11 edited ... When the observable stars are plotted in this way, a pattern emerges. The most prominent featu…
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    When the observable stars are plotted in this way, a pattern emerges. The most prominent feature is the 'Main sequence' which arcs across the diagram from top left to bottom right, with redder, cooler, dimmer stars on the bottom right end, working up through average yellow stars like our Sun all the way up to hot, bright, blue stars on the other end in the top left. In the diagram above, the Sun can be placed approximately between the 'Main sequence' and 'Giants' labels.
    The other main features of the diagram are the clouds in the upper right and bottom left. In the top right are the giants (and supergiants)—massive, very bright, but relatively cool stars—and in the bottom left are the white dwarfs—remains of burnt out stars which are still extremely hot, but not very bright since they are no longer undergoing nuclear fusion.
    The units on the axes can vary. In this diagram, luminosity is measured in solar luminosities i.e. 100Lo = 100 x the luminosity of the Sun. The units of temperature are Kelvins, which is a system of units whose individual sizes are equivalent to ºC, but for which 0K is absolute zero (~-273ºC).
    For a sketching question like this, the main features to include are the shapes and positions of the main sequence and the clouds of white dwarfs and giants; and the labelling of the axes, with the direction in which they are increasing.
    –Andrew
    (view changes)
    1:36 pm
  3. page Q17Mock11 edited ... The other main features of the diagram are the clouds in the upper right and bottom left. In t…
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    The other main features of the diagram are the clouds in the upper right and bottom left. In the top right are the giants (and supergiants)—massive, very bright, but relatively cool stars—and in the bottom left are the white dwarfs—remains of burnt out stars which are still extremely hot, but not very bright since they are no longer undergoing nuclear fusion.
    For a sketching question like this, the main features to include are the shapes and positions of the main sequence and the clouds of white dwarfs and giants; and the labelling of the axes, with the direction in which they are increasing.
    –Andrew
    (view changes)
    1:25 pm
  4. page Q17Mock11 edited January 2011 Mock: Question 17 This is a simple Hertzsprung-Russel diagram: {hr_local.gif} T…

    January 2011 Mock: Question 17
    This is a simple Hertzsprung-Russel diagram:
    {hr_local.gif}
    The Hertzsprung-Russel diagram is essentially a scatter graph of observable stars' luminosity vs. their temperature, which can be assessed by looking at the colours of light being emitted from the star. The letters along the x-axis are the categoric spectral types of stars, which are not essential. Luminosity is increasing with the positive y direction, and temperature increasing with the negative x direction. Both variables are on logarithmic scales, i.e. they do not increase in a linear or direct way, but by increasingly large amounts.
    When the observable stars are plotted in this way, a pattern emerges. The most prominent feature is the 'Main sequence' which arcs across the diagram from top left to bottom right, with redder, cooler, dimmer stars on the bottom right end, working up through average yellow stars like our Sun all the way up to hot, bright, blue stars on the other end in the top left. In the diagram above, the Sun can be placed approximately between the 'Main sequence' and 'Giants' labels.
    The other main features of the diagram are the clouds in the upper right and bottom left. In the top right are the giants (and supergiants)—massive, very bright, but relatively cool stars—and in the bottom left are the white dwarfs—remains of burnt out stars which are still extremely hot, but not very bright since they are no longer undergoing nuclear fusion.
    For a sketching question like this, the main features to include are the shapes and positions of the main sequence and the clouds of white dwarfs and giants; and the labelling of the axes, with the direction in which they are increasing.

    (view changes)
    1:25 pm
  5. file hr_local.gif uploaded
    1:07 pm
  6. file hrdiagram.jpeg uploaded
    1:06 pm
  7. page Q4Mock11 edited ... 3.) A robotic Telescope can take pictures of things that you cannot see with your naked eye. E…
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    3.) A robotic Telescope can take pictures of things that you cannot see with your naked eye. E.G. Andromeda Galaxy
    AKASH PATEL
    
    4 a)
    The students should know where the object is in the sky (eg. North, South...)
    The students should know the weather predictions near the observation day. If there is a high chance of there being cloud, the students may want to reschedule the observation date.
    4 b)
    The students will need a red torch
    The students will need a chair
    4 c)
    An advantage of using a robotic telescope is that the telescope will automatically find the object you are trying to see which saves time looking for the object.
    Sudz Lakhani

    (view changes)
    12:52 pm
  8. page Q7Mock11 edited ... iii) Because the Earth needs to rotate slightly more in order for the Sun to be exactly back …
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    iii) Because the Earth needs to rotate slightly more in order for the Sun to be exactly back where it was at the start of the rotation. This takes longer than it does in comparison to a far away star.
    Martin Macrae :D
    7a) A sidereal day is the time it takes for the Earth to rotate once on its axis. This is 23 hours and 56 minutes.
    b) A solar day is the time taken for a particular part of Earth to face the sun again. This is 24 hours
    c) {http://www.astronomyforum.net/members/magnetar-albums-my-drawings-picture778-day.jpg}
    The diagram shows that it takes 23 hours and 56 minutes for the earth to rotate on its axis once. It then takes the another 4 minutes for the same part of the Earth to face the sun. This is the solar day.
    Sudz Lakhani

    (view changes)
    12:43 pm
  9. page Q18Mock11 edited ... January 2011 Mock: Question 18 a) 4.6 days ... out the absolute magnitude of luminosity …
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    January 2011 Mock: Question 18
    a) 4.6 days
    ...
    out the absolute magnitude ofluminosity using the star.period-luminosity law. Then, using
    ...
    parsecs.
    c) I'LL DO THIS BIT LATER I PROMISEThe heliocentric parallax method can be used to determine the distance to a star, if the star in question is relatively nearby. The position of a star against the fixed background stars is noted, then measured again 6 months later, when the earth is on the opposite side of the sun. The star's shift in position is used to calculate the parallax angle, and then trigonometry can be used to calculate the distance to the star
    *Suitable diagram*

    (view changes)
    11:51 am
  10. page Q4Mock11 edited ... 2 - Pen and paper to record notes c) Using a Robotic telescope will make the pictures more de…
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    2 - Pen and paper to record notes
    c) Using a Robotic telescope will make the pictures more detailed.
    1.) a.)MOON PHASE
    b.)WEATHER CONDITIONS
    2.) a.)CHAIR
    b.) Pencil
    3.) A robotic Telescope can take pictures of things that you cannot see with your naked eye. E.G. Andromeda Galaxy
    AKASH PATEL
    

    (view changes)
    11:04 am

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