Do photons lose energy while travelling through space? Or why are planets closer to the sun warmer?

Question

My train of thought was the following:The Earth orbiting the Sun is at times 5 million kilometers closer to it than others, but this is almost irrelevant to the seasons.Instead, the temperature difference between seasons is due to the attack angle of the rays, so basically the amount of atmosphere they have to pass through.Actually, it makes sense, heat comes from the photons that collide with the surface of the earth (and a bit with the atmosphere) and gets reflected, and there's nothing between the earth and the sun that would make a photon lose energy over a 5 million km travel on vacuum. Or is it? (Note I'm not wondering about the possible lose of energy related to the redshift of the expanding universe.)Which made me wonder…So why then are the planets closer to the sun warmer? It seems silly, the closer you are to a heat source, the warmer it feels, but that's because of the dispersion of the heat in the medium, right? If there's no medium, what dissipates the energy?

Answer 1

First, yes, photons lose energy as they travel. From the Internet: The answer to your first question is yes, for all intents and purposes, photons traveling through intergalactic space could, and in fact do, lose energy due to the expansion of spacetime in the Universe. As the photons lose energy their wavelengths become longer.

But, planets close to a star receive more photons per square unit of surface area than do planets further away because the "rays" of photons spread out in all directions as they travel further away from the star.