Astronomy 122 Distance Education Second Homework Assignment

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  1. Do Interactive exercise #2 that is located in Module 2 Lecture D.

    This exercise refers to identifying elements AX and BX. You may use the measurement widget but do not "publish to global view". Just use that to record the wavelengths which you can then later put in your email document. To the right is an example screen shot for element AX showing the 4 spectral lines (wavelengths omitted) that you would need to match up with the periodic table of elements. The white line at the top labelled 4105/0 is what you slide up up and down to measure the wavelengths of the 4 dark lines. Your response to this question should include


















  2. For main sequence stars, there is a relationship between their total mass and their energy output (which we call the luminosity). Report on the form of this relationship and how it was empirically discovered.




  3. Application of the Inverse Square Law for determining stellar luminosities:

    We have a calibrating star - let's call this star Janelle.

    Janelle has the following properties:

    As an example to how to solve these problems consider this case. We observe Star Example - it has a flux on my detector of 8 units. Independent evidence shows that star Example has an intrinsic energy output of 2 solar luminosites. What is the distance to star Example?

    Well what do we know about star Example compared with our calibrating star Janelle:

    1. First of all, we know that if star Example was at a distance of 20 light years ( the same distance as Janelle), then the observed flux would be 5 times lower. Why, because star Example is intrincially 5 times fainter than star Janelle. So if a 10 solar luminosities at a distance of 20 light years produces a flux of 4 energy units, then a 2 solar luminosity star at the same distance will result in an energy flux of 0.8 units (4/5).

    2. But my observed flux is 8 units, not 0.8 units. Therefore star Example must be at at distance thats closer than 20 light year so that the received flux is higher.

    3. Now I notice that the observed flux (8 energy units) is actually 10 times more than it would be if star Example were at 20 light years (8/.8) = 10.

    4. Now I apply the inverse square law - to increase the flux by a factor of 10, I must move to star closer to me by a factor of the square root of 10. Thus the distance to star Example is 20/ √ 10  or about 6 light years.

    There are four other stars in the sky whose luminosity or distance or energy flux we want to obtain using Janelle as the reference point via the same scaling argument I just went through:

    Show all work/reasoning in answering these questions:





  4. Refer to the left diagram and answer this series of questions:

      a) List all the possible values of photon energies that this atom "emit" if the electron is moved to the highest energy level shown in this diagram (e.g. energy level = 12)


      b) If an incoming photon has energy = 9 units and the electron is in the ground state (as pictured), what will happen to the incoming photon and the electron?



      c) if the electron is in the first excited state (e.g. energy level =5) and in incoming photon of of energy = 5 units hits the atom, what will happen to that photon and the electron?