Explore why the night sky appears dark despite the infinite universe of stars.
Calculate theoretical sky brightness, visible star counts, and understand the cosmological implications of Olbers' famous paradox about the darkness of space.
Click on any example to load it into the calculator.
Modern cosmological parameters based on current observations and the ΛCDM model.
Universe Age: 13.8 billion years
Star Density: 0.1 stars/pc³
Avg Luminosity: 0.5 solar units
Light Speed: 299792 km/s
Observable Radius: 46.5 billion ly
The classical assumption that led to Olbers' paradox - infinite, static universe.
Universe Age: 999999 billion years
Star Density: 1.0 stars/pc³
Avg Luminosity: 1.0 solar units
Light Speed: 299792 km/s
Observable Radius: 999999 billion ly
Conditions shortly after the Big Bang when stars were first forming.
Universe Age: 1.0 billion years
Star Density: 0.01 stars/pc³
Avg Luminosity: 10.0 solar units
Light Speed: 299792 km/s
Observable Radius: 3.4 billion ly
A universe with much higher star density, showing the paradox more dramatically.
Universe Age: 13.8 billion years
Star Density: 1.0 stars/pc³
Avg Luminosity: 2.0 solar units
Light Speed: 299792 km/s
Observable Radius: 46.5 billion ly