Ask A Scientist© Astronomy Archive

Author:      emilio vargas iii 
I am a 6th grade science teacher and my students want to know how scientist
are able to determine the temperature of the Sun's surface and it is core. 
Also the temps of the other planets in our solar system, especially pluto.   

Response #:  1 of 1
Author:      jasjeet s bagla
The temperature of the surface of the Sun can be determined in various ways. 
We know how much energy we receive on Earth per unit time over a unit area
facing the Sun.  Then knowing the distance to the Sun, we can estimate total
energy being emitted by the Sun.  The total energy emitted per unit time per
unit area is related to temperature in a known way.  This can be used to
find the Surface temperature of the Sun.
Sun is a gaseous sphere and it seems to be a stable object.  Our existence
tells us about the stability of the Sun.  We think that gravity holds the
Sun together.  In that case the gas pressure must be enough to balance the
gravitational force.  We know the relation between gas pressure and 
temperature, this is then used to calculate the core temperature.  This is 
the simplest method I know of, other methods take into account some other
effects as well but answers do not change much.

Temperature of Planets is measured in a slightly more complicated way. 
Known properties of reflected light are used to probe the reflecting
material, in the planets' atmosphere.