Light Pollution Sky Glow Calculator

Light Pollution Sky Glow Calculator

Planning a stargazing trip and wondering how much a nearby city's lights will wash out the night sky? Sky glow - the diffuse brightening caused by artificial light scattering off atmospheric particles - has been empirically observed to scale with population and fall off steeply with distance.

Sky Glow Index ≈ Population / Distance^2.5

Example

A city of 500,000 people, 20 km away:

Index = 500,000 / 20^2.5 ≈ 279.5 (significant light pollution impact expected)

Why Distance Matters So Much

The steep 2.5 exponent means sky glow impact falls off much faster than a simple inverse-square relationship would suggest - doubling your distance from a city dramatically reduces its sky glow contribution, which is exactly why serious stargazers and astrophotographers often travel considerably further from a major city than casual intuition might suggest is necessary for genuinely dark skies.

What This Model Doesn't Capture

This is a simplified relative comparison index, historically referred to in astronomical light pollution research as following "Walker's Law" - actual sky glow at any specific location depends heavily on local lighting technology and fixture shielding, atmospheric humidity and particulate levels, and intervening topography, none of which this basic population-and-distance model accounts for.