The Cosmic Distance Ladder – How We Measure the Universe

How do astronomers know a galaxy is two million light years away, or thirteen billion? This episode climbs the cosmic distance ladder rung by rung, from bouncing radar off Venus, to parallax and the Gaia satellite, to pulsating Cepheid stars and exploding white dwarfs, to the redshift of the expanding universe itself — and arrives at a genuine, unresolved disagreement between two ways of measuring the universe's expansion rate.

You'll come away understanding how radar and parallax give us rock-solid distances close to home, how Henrietta Leavitt's discovery about Cepheid variable stars unlocked distances across galaxies, why Type Ia supernovae work as standard candles reaching billions of light years, how each rung of the ladder is calibrated against the one below it, and what the Hubble tension is, and why it remains one of the open questions in cosmology today.

Talking Science is sponsored by Kinsoft. Visit www.kinsoft.com.au

Further reading: NASA – "Hubble Constant" and distance ladder explainers; ESA – Gaia mission science pages; Nature – reporting on the Hubble tension; Scientific American – features on standard candles and the expanding universe.