LearnCosmology & scaleBuilds on the rest
The cosmic distance ladder
The chain of overlapping techniques by which distances are measured, each calibrated against the shorter rung below it.
Why it matters
No single method spans from the nearest star to the edge of the observable universe. Every cosmological distance therefore inherits the uncertainty of every rung beneath it.
Rests on
- Stellar parallaxThe tiny annual shift in a nearby star's apparent position, caused by the Earth viewing it from opposite sides of its orbit.
- The inverse-square law of brightnessThe apparent brightness of a source falls off as the square of its distance, because the same light is spread over an expanding sphere.
- Doppler shift and redshiftMotion along the line of sight stretches or compresses the wavelength of light, moving spectral lines toward the red or the blue.
8 concepts in the full chain back to first principles.
Leads to
Nothing here builds on it yet.