Phys1190 Short Answer

1. What were the key observations that led to the acceptance of the heliocentric or Copenican model of the Solar system, in preference to the geocentric or Ptolemaic model?  (100 words, 2 marks)

The key observation for acceptance of heliocentric model included Galileo’s discovery of four large moons of Jupiter provided evidence that that the solar system contained bodies that did not orbit Earth, as suggested by Aristotelian Cosmology and Roman-Catholic beliefs.

In addition, Kepler’s observation of Mars, in which astronomers had difficulty in predicting its position, determined that the all the planets had an elliptical orbit around the Sun, further reinforcing the heliocentric model that Sun was the perceived centre of the Solar System.

2. Glass photographic plates were once the standard detector for astronomical imaging. Describe the type of detector that has replaced photographic plates and outline what its advantages are. (100 words, 2 marks)

The invention and development of the electronic detectors in the 1980s, particularly the Charged Coupled Devices (CCD) had replaced the glass photographic plates. The advantages of using the CCD include:

* The sensor is very sensitive to light and is comparable to standard film allowing fainter objects to be observed;

* Responds to the entire visible spectrum, and even into the near infra-red; and

* Provides immediate results that are recorded directly to a computer.

3. What is meant by the "Early faint sun paradox" in the history of the Earth and how has the "paradox" been resolved? (150 words, 3 marks)

The “Early faint sun paradox” refers to the contradiction between the observations of liquid water present early in Earth’s history astrophysical expectation that the Sun would have had a reduced intensity of approximately 70% of today’s output. The key issue raised is that the reduced output from the Sun would not have been sufficient to maintain a liquid water surface in contrary to the...