I'm new to physics and am just going through some of the free online classes at World Science U, and after watching this video on the nature of the speed of light and its constancy, a question came to mind about photons. (Video: YouTube Video, World Science U course)
I know that photons don't have mass, but what happens when photons — even the photons from distant stars — reach us? Are we merely observing the occurrence of photons moving through space relative to us, or are we really being "bathed" in photons? I know that when I observe rain, I can both observe it from a distance but could also be immersed in it as well if in the path of that rain. But with distant starlight, are we just observing it or are the photons actually reaching and penetrating the earth around us? If they are penetrating, does science tell us what is actually happening on an atomic or sub-atomic level?
Answer
Yes, the photons actually reach you, like rain falling on you, not like watching rain from a distance. When you see a star, photons from the star actually enter your eye.
In for example rods of your eye, the photon causes a molecule of retinal to react by change from cis to trans isomer.
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