Astronomy
The Cosmic Distance Ladder and the Measurement of the Hubble Constant
Quick fact
The cosmic distance ladder is a series of methods, each calibrated by the previous rung, that allows astronomers to measure distances to galaxies billions of light-years away. The Hubble constant, derived from this ladder, is famously uncertain, with different methods giving values that differ by about 10%, a discrepancy known as the Hubble tension.
Why this is interesting
You might know that galaxies are flying apart, but did you know that measuring exactly how fast they are moving requires a chain of cosmic measuring sticks that astronomers call the distance ladder?