Astrophysics’ True Star: Cepheid Variables

Anthony Edmonds, Staff Writer

Our universe is on a scale so significant to us that it is nearly incomprehensible. After all, it’s all we’ve ever known and all that we have ever experienced. Of course, one day, we may become an interstellar species, and be capable of furthering our development by moving to the stars. However, the universe will remain vast and empty, full of mystery and wonder.

But with all this vast emptiness came the introduction of one of the greatest problems in modern astronomy: distance. For centuries, astronomers have inquired into its seemingly eternal vastness of the cosmos. However, it seems that this “eternal” vastness may have a limit, meaning our universe may have a measurable size. 

To the average person, the concept of measuring a universe seems near impossible. However, thanks to American astronomer Henrietta Swan Leavitt, we have an idea of how to approach this dilemma. Leavitt was responsible for providing us with our understanding of a type of star called a Cepheid variable. Leavitt originally studied multiple Cepheid variables that change in luminosity at Harvard Observatory. These Cepheid variables have a specific period at which they would change luminosity, either brightening or dimming, and this could be plotted out on a graph. Leavitt, measuring this function, decided to compare the period of change to the brightness of our sun, and found that the brighter the star, the longer it took to cycle through dimming and brightening. This was important, as this regular and uniform function allowed astronomers to infer the brightness of a cepheid variable star by calculating its period. 

According to the NASA Star Child site, “From the period and Leavitt’s plot, we get the brightness at the distance of one light-year … We can also measure the brightness on Earth. The brightness at the distance of one light-year will be larger than the observed brightness due to the fact that brightness drops like the square of the distance. From these numbers, one can extract the distance to the [star].”  The reason that finding our distance to Cepheid Variables is important is that by using the equation mM = 5 log d – 5, where m is the apparent mass of the object, M is the total mass of the object, and d is the distance to the object in parsecs, we can calculate the distance of any object relative to that of the cepheid variable, and from there, the cepheid to Earth. 

This is by far one of the most influential discoveries in modern astronomy. Cepheid Variables are the primary reason we can calculate our distance to most objects, as well as the universe’s expansion. A seemingly innocuous set of stars that varied in brightness over time allowed astronomers to figure out how far things are from us, and later on, helped to prove the existence of galaxies aside from our own. On top of that, Cepheid variables are even visible to us here with the naked eye. They can be quite bright in some parts of the world, and many pictures of them are quite grandiose.

 Beholding the grandeur of the universe is intimidating, and its vastness will never go away, however, as more of us turn to science, making discoveries like the magnificent Cepheid Variables, and gaze upon the stars like those before us, we begin to understand more about the place we live in. As night falls once again, consider looking up, and absorbing all the emotions the universe may bring.