What did that graph of wavelength and emission mean?
The plot of intensity versus wavelength is known as a “spectrum”. It tells you how much radiation is present at a particular frequency. For instance, if you have a curve which has a high value around wavelengths corresponding to red light, and a low value around wavelengths corresponding to blue light, then there is more red light than blue light coming from the object, and the object will appear red. If the spectrum has narrow spikes, those are emission lines: there’s a lot of radiation at those particular wavelengths. If the spectrum has narrow dips in an otherwise continuous curve, those are absorption lines: radiation of particular frequencies is missing. The example we saw in class was the spectrum of Mars. The left hump was the thermal spectrum of reflected light from the Sun, modified by absorption due to chemicals in Mars’ surface and atmosphere. The right hump at higher wavelength (lower frequency and energy) was the thermal spectrum due to Mars itself (all bodies radiate th
