If photons do not split, and light travels in straight lines then at x distance from a star there should be gaps in the straight line light tangents (which would make the star unobservable) However this doesnt happen which suggests the light field expands but how? Put another way if a light wave is present then this suggests that with wave particle duality the number of photons should increase to maintain the perimeter of the expanding field of light. With light speed at around 300,000 kms is there a formula for light wave frequency (photon multiplication) expansion?


1 Answer 1


The light from a star is distributed uniformly among the surface area of a sphere enclosing it, much like how a Gaussian surface enclosing a point charge has an equal $\vec E$ field everywhere on its surface. As such, it does "expand" in the sense that a larger Gaussian surface means that there is a lower luminosity per unit area (i.e., flux) from the star.

The light field also expands for two more reasons. The first is what is called "seeing" in astronomy, which is the blurring of stars' light because of turbulence in the atmosphere. The second reason for the "field" expansion is because the light must pass through some kind of aperture detector (either a telescope or your eye), which creates circular diffraction patterns on the viewing surface.

  • $\begingroup$ Thank you. So does this mean that photon density decreases hence resulting in a decrease in luminosity? If so then the distance between photons should be greater as the distance from the sun increases. I like your answer though i had thought photons must split and lose luminosity. $\endgroup$
    – Darren
    Feb 13, 2018 at 3:22
  • $\begingroup$ If by photon density, you mean the number of photons per unit area, then I think that makes sense. $\endgroup$
    – zh1
    Feb 13, 2018 at 3:29
  • $\begingroup$ Ok so if the distance between photons increases over distance then the constant emission of light would explain why at a distance we dont miss the observation of a star when the distance between photons is greater than the width of an eyeball. $\endgroup$
    – Darren
    Feb 13, 2018 at 3:52

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