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29 September 2026 2518 stories tracked

Glossary · Stars & Supernovae

Cepheid variable

A star that pulses at a rate set by its true brightness, which is how the universe got measured.

Cepheids swell and shrink in a regular cycle of days to months, and Henrietta Leavitt found in 1908 that the length of that cycle tracks their intrinsic luminosity. That turns a stopwatch into a distance meter: time the pulse, deduce the true brightness, compare it to how bright it looks, and you have the distance. Hubble used one in Andromeda to prove other galaxies existed, and Cepheids remain the first rung of the distance ladder whose upper rungs now disagree about the expansion rate.

Related terms

Magnetar A neutron star with a magnetic field a thousand trillion times Earth's. Supernova (Type Ia and Type II) Two unrelated ways for a star to explode, useful for two entirely different reasons. The main sequence The long, stable middle age a star spends fusing hydrogen in its core. Hertzsprung–Russell diagram The single plot that organises everything about stars.

Questions

What is Cepheid variable?

A star that pulses at a rate set by its true brightness, which is how the universe got measured.

Why does it matter?

That turns a stopwatch into a distance meter: time the pulse, deduce the true brightness, compare it to how bright it looks, and you have the distance. Hubble used one in Andromeda to prove other galaxies existed, and Cepheids remain the first rung of the distance ladder whose upper rungs now disagree about the expansion rate.

Written and computed by . Corrections and errors to hello@cantinalabs.dev.