| 1.
| You have observed the spectrum of a nearby star of known parallax.
What can you determine from: |
| (a) | the wavelength at which its spectral intensity peaks (i.e. its colour)?
| (1) |
| (b) | the positions and strengths of the absorption lines in its spectrum?
| (2) |
| Assuming that it is too small to show a visible disc when imaged by your telescope,
how would you go about estimating its size?
| (1) |
| Under what circumstances could you determine its mass?
| (1) |
|
| 2.
|
How does the Sun compare in mass and brightness with:
|
| (a) | the thirty nearest stars?
| (1) |
| (b) | the thirty stars which appear brightest in our night sky?
| (1) |
| Using your answers to (a) and (b), and any other relevant information you possess,
critically discuss the often-made statement that "the Sun is an average star".
| (3) |
|
| 3.
| Compare and contrast
|
| (a) | planetary nebulae and supernova remnants;
| (2.5) |
| (b) | main-sequence stars and red giants.
| (2.5) |
|
| 4.
| (a) | Globular cluster stars are typically low in heavy elements,
whereas stars in open clusters have higher (solar) heavy element content. Why?
| (2) |
| (b) | Explain why the element iron has special significance in
understanding the evolution of massive stars.
Why is it less important in the evolution of stars like the Sun?
| (3) |
|
| 5.
| List the properties you might expect to observe in a pre-main-sequence Sun-like star.
| (5) |
|
| 6.
| Describe the Hubble tuning-fork classification system for galaxies.
| (5) |
|
| 7.
| Explain how you would distinguish between:
|
| (a) | an E0 galaxy and an E4 galaxy;
| (1) |
| (b) | an Sbc galaxy and an SBc galaxy;
| (2) |
| (c) | an E6 galaxy and an S0 galaxy;
| (1) |
| (d) | an SB0 galaxy and an SBa galaxy.
| (1) |
|
| 8.
| If the Universe contains one atom of helium-4 for
every ten atoms of hydrogen, how many neutrons were produced in the
early universe for every 100 protons?
| (2) |
| Briefly explain how we know that almost all of today's
helium was produced in the big bang, and not generated by hydrogen fusion in stars.
| (2) |
| Name one other isotope also believed to be produced in the early
universe.
| (1) |
|
| 9.
| What sort of planet would be easiest to discover using:
|
| (a) | Doppler shift measurements?
| (12/3) |
| (b) | astrometry (i.e. careful measurements of the position of the star)?
| (12/3) |
| (c) | transit observations (i.e. careful measurements of the apparent
brightness of the star)? | (12/3) |
|
| 10.
| Why might you not expect to find life on a planet orbiting
|
| (a) | a massive class B main sequence star?
| (1) |
| (b) | a very low mass class M main sequence star?
| (1) |
| (c) | a red giant?
| (1) |
| What observations of an Earth-like planet circling a nearby
star would you make to provide evidence for life on that planet?
| (2) |
| 1. |
The Sun is presently on the Main Sequence of the Hertzsprung-Russell diagram.
Explain:
|
| (a) | how it is currently generating energy;
| (1) |
| (b) | what will happen to it after it leaves the main sequence,
in terms of its location on the HR diagram and the processes occurring in its interior;
| (5) |
| (c) | why it will not explode as a supernova;
| (1) |
| (d) | what it will look like shortly after fusion processes have stopped.
| (3) |
| How and why does the time spent on the main sequence depend on the mass of
the star? Carefully explain why the time spent on the main sequence is so much longer
than the time spent in other evolutionary stages up to the end of fusion.
| (5) |
|
| 2. |
(a) | Describe the various ways in which
elliptical galaxies differ from spiral galaxies.
| (5) |
| (b) | How do we think large elliptical galaxies are produced?
How does this theory match up with (i) the properties you discussed in part (a) and
(ii) our observations of very distant clusters of galaxies?
| (6) |
| (c) | You are an alien astronomer living on a planet
located in an elliptical galaxy. Although you have fourteen legs and are covered in scales,
your eyes (all six of them) happen to be very similar in sensitivity and colour response
to human eyes. What does the night sky look like from a good dark observing site on your
planet, compared to the night sky from a similar site on Earth?
| (4) |
|
| 3. |
(a) | Explain why we do not think the light isotopes deuterium
(hydrogen-2), helium-4 and lithium-7 are made entirely in stars,
like the rest of the elements heavier than hydrogen.
| (3) |
| Briefly explain how these isotopes can be accounted for
in the Big Bang theory.
| (2) |
| (b) | Describe the main features of the cosmic microwave
background radiation, and explain how this is produced in the Big Bang theory.
| (5) |
| (c) | What is Olbers' Paradox,
and what is its significance for cosmology?
| (5) |
|
| 4. |
How have the majority of planets around other stars been detected so far?
Explain why and how this method of detection biases the properties of the planets discovered.
| (5) |
| Describe one other method by which planets
(not extraterrestrial civilisations) around other stars could be detected.
Critically discuss how using your chosen method would bias the properties of detected planets.
| (5) |
| The Drake Equation is an expression for the
number of technological civilisations in our Galaxy. List the factors which enter
into this equation, briefly discussing which of them can be evaluated
using existing or planned observations.
| (5) |
|
| 5. |
Write short essays on any three of the following:
|
| (a) | binary stars; | (5)
|
| (b) | black holes; | (5)
|
| (c) | the search for dark matter; | (5)
|
| (d) | whether other planets may host
technological civilisations. | (5)
|
| Note: this question, which is based on the seminar titles,
will be in the exam paper.
|
