* Cepheid variable stars: These are stars that pulsate in brightness over a regular period of time.
* Period-luminosity relationship: Leavitt found that the longer the period of a Cepheid variable star, the brighter it is intrinsically (meaning its actual brightness, not just how bright it appears from Earth). This relationship is crucial for measuring distances in space.
Here's why this was so important:
* Measuring distances: Before Leavitt's discovery, astronomers had difficulty determining distances to stars beyond our own galaxy. The period-luminosity relationship provided a "standard candle" – a way to measure a star's true brightness and then calculate its distance based on how bright it appeared from Earth.
* Unlocking the universe: This discovery opened up a whole new dimension in astronomy. It allowed astronomers to measure distances to galaxies far beyond our own, leading to the understanding of the vastness of the universe and the expansion of the universe.
Leavitt's work laid the foundation for Edwin Hubble's discovery of the expanding universe, a monumental breakthrough in cosmology.