Astronomy, Our Place in the Universe: Short answer assessment (for MQuni)

grade:– 37.5/55 (75%)

1. Visit the Rotating Sky Explorer at: http://astro.unl.edu/naap/motion2/animations/ce hc.html Set the observer’s latitude and longitude to the correct values for Sydney. Set the Star Controls tab to display the constellations of Orion and the Southern Cross. Switch on as many display settings as you like (I recommend checking all the boxes first and later removing ones that are less useful). 4 marks 
   
   (a) Which of the two constellations you have displayed is circumpolar from Sydney? (b) What is the meaning of the line that runs through the constellation of Orion?
   (c) Are there any places on Earth where Orion will be a circumpolar constellation? (d) How does the sky appear to rotate if you move the observer to the North Pole? (e) How does the sky appear to rotate if you move the observer to the Equator?
2. Describe why we are able to see 59% of the Moon’s surface from Earth. 4.5 marks
3. Two bodies are orbiting each other in a binary system. Draw a plausible sketch of the orbits in the two cases given below, being sure to mark on the orbital path of each body and the centre of mass of the system. 5 marks
   (a) The two bodies are stars are of equal mass.
   (b) One body is a Sun-like star and one is a small rocky planet.

4. Visit the Doppler Shift Demonstrator at http://astro.unl.edu/classaction/animations/light/dopplershift.html. Set the source to emit radiation. 5 marks
   
   1. (a)  Move the source towards the observer. What happens to the wavelength of the observed radiation?
   2. (b)  Now move the source away from the observer. What happens to the wavelength of the observed radiation?
   3. (c)  What happens if the source is moving purely tangentially to the observer (i.e. neither towards or away)?
   4. (d)  From this answer the following: The doppler shifting of radiation from astronomical objects allows us to measure which component of their velocity?
      i. Radial (towards/away from us)
      ii. Tangential (along side us; neither towards or away)
   5. (e)  The Hydrogen alpha spectral line is measured experimentally in the lab to have a wave- length of 656.28 nm. Observed from a distant emission nebula it is seen to have a wavelength of 656.58 nm. State whether the line has been redshifted or blueshifted, and what this enables us to tell about the motion of the nebula relative to the Solar System.
5. Look up the following telescopes online: 3 marks
   
   1. (a)  The Atacama Large Millimeter Array
   2. (b)  The Chandra X-Ray Observatory
   3. (c)  The Spitzer Space Telescope
   Pick one and write a few sentences about it, making sure to include what part(s) of the electro- magnetic spectrum it can observe. Describe one type of astronomical object that this telescope is well-suited to observe, justifying your answer in terms of the type of radiation they emit and, if relevant, the resolving power of the telescope.

6.  Describe how the Sun generates energy. Why can this process only occur in the Sun’s core? 

4 marks

      7.  Why are parallax measurements only possible for relatively nearby stars? If we set up a colony        on Mars and measured parallax from there, would we be able to measure the distances to more or fewer stars (and why)? 3 marks

     8.   Explain why emission nebulae are signposts of recent and/or ongoing star formation. 5 marks

Challenge question! The figure below shows two snapshots of supercomputer models of molecular cloud collapse (credit: https://www.astro.ex.ac.uk/people/mbate/):

In these images, the white dots are newly-formed stars, and the red/orange stuff is the gas of the molecular cloud. The two snapshots were both taken at the same time (∼89,000 years after the model started), and the simulations were identical except for one thing: the “stars” formed in the left-hand model were just treated as inert blobs of gas, whereas the stars on the right hand model emit radiation (as real stars do!). 

   9.  A quick glance will tell you that the model on the left has formed many more stars in the same time period. (Count the dots!) With reference to what we have learned about the factors that oppose molecular cloud collapse, why do you think this might be? 0.5 marks

  10.  Finally... Visit http://apod.com/ and use the search function to find a picture related to some- thing we have covered in the course so far (if we haven’t done it in the course you won’t get the marks!) Provide the image and a three-sentence caption condensed from the description available on the page. 3.5 marks