Remember that
bodies radiate energy at all wavelengths.
Also,
the
wavelength of peak emission corresponds to
the temperature of the body.
The other thing you need to know is the atmospheric
compositions of terrestrial planet (Venus,
Earth, Mars) atmospheres.
We will talk about this next time. For
now, know that Venus' atmosphere
is mostly CO2 with a little N2;
Earth's atmosphere
is mostly N2 with a little CO2;
and Mars' atmosphere is mostly CO2 with
a little N2.