Observational astronomy - 555

Homework 1

Due: Feb 8 2018

1) a) What is the difference between a flux and a flux density?  [1 point ]
   b) Magnitudes and F_lambda are both flux densities, and can be converted into
       one another. Give the conversion. [1 point ]
   c) Explain why it is more precise to give a flux density in F_nu than in F_lambda
      for a given AB magnitude. [2 points ]
   d) Sketch how the conversion from AB magnitude to F_lambda can go
      wrong for the U band. [ Hint: use the word 'atmosphere' ]   [ 4 points ]

2) Play with the sky model calculator. Use the calculator to answer the following
    questions:
   a) What is the main advantage of going to space when observing at a wavelength
      of 1.4 micron?  [1  point ]
   b) What are the dominant contributions of sky emission and absorption (separately)
       at 0.25, 0.5, 2.5, 5, and 25 micron ?
      ( so give, for each wavelength, the dominant emission contributions and the
         dominant absorption contribution)
      [ 3 points ]
   c) speculate how you can mitigate, or correct for, the effects in b *without*
       going to space
      [ 4 points ]