Cepheid Variables are the Bedrock of the Cosmic Distance Ladder. Astronomers are Trying to Understand them Better

One of the most fundamental questions astronomers ask about an object is “What’s its distance?” For very faraway objects, they useas “distance rulers”. Astronomers call these pulsating stars “standard candles”. Now there’s a whole team of them precisely clocking their speeds along our line of sight.

Some pretty well-known stars are Cepheid variables. For example, Polaris—the well-known “North Star” is one, as is RR Puppis, Delta Cephei, and Eta Aquilae—all visible from Earth. Why these stars pulsate is still being studied but here’s a very basic look at their process. The core of the star produces heat which heats the outer layers. They expand, and then cool. Radiation is escaping, which makes the star appear brighter.

Calibrated Period-luminosity Relationship for Cepheid variables. Courtesy Spitzer Space Telescope/IPAC.

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