Cepheids: Predictable Measurement Tools in a Mysterious World

In a world where many things are unclear, it is good to have a few metrics that behave predictably. Cepheids – variable stars – are such a measuring instrument.

In the constellation Cepheus, just above Kassiopeia, about 887 light-years away is the star Delta Cephei. We’ve known since 1784 that this is a variable star: over the course of a few days, the star’s brightness increases and then decreases again. This pattern repeats every 5.37 days.

Thousands of variable stars

At the beginning of the 20th century, it became clear that there were as many stars as Delta Cephei. Research conducted on thousands of stars has shown that there is a clear relationship between the period of the pulsation and the brightness of the stars.

Why is CEVED considered a reliable measurement tool? We can measure two things very precisely in such a star: the pulsation period and the brightness. But this brightness depends on the distance from the star, and therefore is relative. Thanks to this knowledge, we can thus determine the distance of each variable star from Earth.

expansion of the universe

As a result, Cepheids are like standards in the starry sky, by which we can determine all kinds of distances. This has yielded many benefits to science – for example, in 1929 astronomers were able to determine that the universe must be expanding.

Do you want to know the exact cause of the cephed heartbeat? Then listen to Hens Zimmerman’s column.