I'm glad you found it helpful.
Have you heard of the black-body curve? The Planck law?
A perfect 'black body' (i.e. one which does not reflect any light at all) will give off electromagnetic radiation. If you plot the intensity of that radiation against wavelength (or frequency), you get a very distinct curve. Around the end of the 19th century the shape of this curve was pretty much known, from experiments. And both the long wavelength tail and the fact that the peak wavelength decreased as the temperature increased could be explained, by separate equations - the Rayleigh-Jeans Law and Wien's Displacement Law, respectively - but there seemed no way to get (derive) the actual curve from the then theory of electromagnetism (Maxwell's equations, in a nutshell). This was maddening, because that theory was so spectacularly successful otherwise.
Along came Max Planck, who introduced the concept of the photon, a quantum of electromagnetic energy; with this, he could produce a curve that matched the observational data very well. But he thought of the photon as a computational aid only, a sort of trick; in 1905 Einstein took the idea and ran with it, and showed that it explained the experimental data on the photoelectric effect,
if you assume photons are real.
It turns out that lots of astronomical objects radiate with a spectrum close to that of a black body, the Sun is one such (HII regions and planetary nebulae are exceptions).
Here is a website which explains this in more detail.