Extra Problems - Light and Atoms

You will find the following numbers useful.

The speed of light is 3x105 km-sec-1.

1 AU is 1.5x108 km.

One year = about 3x107 seconds.

  1. How long does it take light to travel from the Sun to Neptune? (Neptune is roughly 30 AU from the Sun).
  2. A star has surface temperature of 18,000 K. Use Wien's Law to find at what wavelength it radiates most strongly.
  3. A dim star radiates most strongly at 1500 nm. Use Wien's Law to find its surface temerpature.
  4. A galaxy shows a spectrum line at 800 nm which in the laboratory is at 600 nm. What is the galaxy's speed?