Lecture 13 4/8/2013 3:29:00 PM
Astronomy with non-visible light Spectroscopy
Why look at other types of light?
Different types of sources emit different ranges of wavelengths
Cosmic microwave background:
o Shows us the last remaining heat from the big bang and gives
us clues to the early history of the universe.
Reflecting telescopes for radio waves.
Since radio waves have larger wavelengths, we need large mirrors
to get good angular resolution.
Another way to improve angular resolution: combine signals from
In most ways, infrared optics are not that different from visible
light. The problem is that earth’s atmosphere blocks a lot of IR.
IR telescopes also need to be insulated from heat.
Spectroscopy: getting more information from light:
We can learn more from light if we understand more about how
light interacts with matter: how it is emitted and absorbed.
o Breaking light from an object into its different wavelengths,
and comparing the amounts of light emitted at different
Three basic types of spectra:
Continuous (thermal radiation)
o A hot, dense object emits light at all wavelengths at once in a
o Examples: a standard incandescent light bulb, the sun, a
glowing heating coil on the stove, a human body. o This emission is also called blackbody radiation.
o The spectrum depends on the temperature.
o Stefan-Boltzan Law:
Hotter objects emit more radiation than cooler ones.
o Wien’s Law:
Hotter objects emit more protons with a higher average