The launch of the James Webb Space Telescope in the beginning of 2021 opened a new window to gaze into our vast universe. Current observatories work night and day to provide insight into the nature of the cosmos: from planets swallowed by their stars, to streams emanating from the accretion disk of black holes, or even the interaction between galaxies tens of thousands of light years away. Thanks to them, most of us have grown up understanding the vastness and beauty of the universe we live in.
However, this notion of immensity is relatively new. A hundred years ago, the most popular theory claimed that the Milky Way contained all the stars in the Universe. Any other observable celestial objects were catalogued as nebulae sitting at its edges. Back then, astronomers lacked a technique for measuring distances that could help them put this theory to test. The only known working methods, parallax and triangulation, were primarily accurate at scales smaller than the Milky Way.
The great breakthrough came from the work of Henrietta Swan Leavitt. In the early 1900s, when women were not allowed to operate telescopes or even sign their own scientific work, this college graduate worked at Harvard as a human computer. She was tasked to measure and catalog the brightness of variable stars in the Small and Large Magellanic clouds. That is when she noticed that the period of variability of these stars, called Cepheids, is proportional to their luminosity.
In astrophysics, the amount of attenuation that the light suffers since it is emitted until it reaches us is proportional to the distance that it travels. Thus, we can compare the intrinsic luminosity of Cepheids to the brightness that we measure on Earth, and know how far away they are. This made Cepheid stars the first “standard candles”: sources with known luminosity that allow astronomers to measure the distance to the places they inhabit. Cepheids became the first step in the “cosmic distance ladder”: the collection of techniques employed in astronomy to measure distances at different scales. Leavitt’s discovery allowed
other astronomers in the 1920s, like Edwin Hubble, to measure the distance to neighbouring galaxies, and realize that the Milky Way is just one of the many islands of stars left to explore in our Universe.
MSc in Astrophysics and Particle Physics.
PhD candidate working in the field of Galaxy Evolution and Large Scale Structure.