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?