THE UNIVERSITY
of LIVERPOOL





SUMMER 2001 EXAMINATIONS

Bachelor of Science: Year 1

Bachelor of Science: Year 2

Master of Physics: Year 1

Master of Physics: Year 2

ASTRONOMY FUNDAMENTALS

 

 

TIME ALLOWED: 1 hour 15 minutes

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Answer both questions.

The questions carry equal marks.

The marks allocated to each part of a question are indicated in square brackets.

In the event of a student answering both parts of the either/or question and not clearly crossing out one answer, only the answer to part (a) of the question will be marked.

1. Answer all parts of this question:

1. A star has Right Ascension 10 hours 00 minutes and declination +20^o. At what time of the year does the star transit the observer's meridian at local midnight? If the star is observed at the La Palma Observatory whose latitude is 28^oN, what would be its altitude above the observer's horizon when it transits? [5]

2. A nova is observed to have visual magnitude at peak brightness m_V = +8. We know from comparison with other novae that its peak absolute visual magnitude M_V = -8. Calculate the distance to the nova (neglecting interstellar extinction). What is the cause of this extinction, and if not accounted for in the above calculation, what effect will it have on the derived distance? [5]

3. What are the main characteristics and evidence for existence of (i) the Oort Cloud and (ii) the Kuiper Belt? [5]

4. Briefly describe the formation and pre-main sequence (PMS) evolution of a star like the Sun. [5]

5. Sketch the "tuning fork" diagram describing the Hubble Sequence of galaxy type. Briefly describe the three main families of galaxies represented here. [5]

2. Answer either (a) or (b):

1. Briefly describe the main characteristics, with sketched diagrams as appropriate, of the following as light detecting devices in astronomy: (1) the eye; (2) a photographic plate, and (3) the CCD camera. Highlight in your answer the advantages and disadvantages of each for astronomical applications. [14]

   The Liverpool Telescope (LT) has a primary mirror 2m in diameter and an effective focal length at the Cassegrain focus of 20m. The CCD camera used at this focus is a square array with 2048 pixels on a side. Each pixel is 15 by 15 microns. Calculate (1) the f-ratio of the telescope; (2) the plate scale at the Cassegrain focus in arcseconds per mm; (3) the field of view of the CCD camera in arcminutes, and (4) the theoretical diffraction limit at visible wavelengths (550 nm) of the telescope. (NB: there are 2.06x10⁵ arcseconds in 1 radian). [5]

   The Hubble Space Telescope (HST) has a primary mirror only marginally bigger than the LT. Briefly describe the major advantages and any disadvantages that the HST has over a similar telescope placed on the surface of the Earth, even at the best astronomical site. What techniques are being developed to overcome one of the major disadvantages of the Earth-based large telescope? [6]

2. In a homogeneous and isotropic universe, we can represent all distances s by a dimensionless number x multiplied by a universal time-dependent scale factor R(t), such that s = x R(t). Show that this leads naturally to Hubble's Law and hence obtain an expression for Hubble's Constant in terms of R. [4]

   Define the cosmological density parameter W_O and describe its use in defining "open", "closed" and "flat" universes. Sketch a graph of R versus t for the three cases W_O = 0, W_O= 1and W_O > 1. [10]

   Describe the current debate about the value of W_O making reference to the concept of dark matter, conflicts over the age of the Universe measured in different ways, and the re-introduction of Einstein's cosmological constant L. [11]