Variable star observing has a fascinating history that leads back to the discovery of the first variable star, Omicron Ceti (Mira the "wonderful") by astronomer (and pastor) David Fabricius in 1596.

Two and a half centuries later, Friedrich Argelander of Germany realized the significance and importance of observing variable stars to the development of astrophysics. In addition, Argelander is justly famous for his production of the first modern star atlas, the Bonner Durchmusterung ("Bonn star survey") published during 1859-1862.

Writing in the Journal of the Royal Astronomical Society of Canada (JRASC), David Chapman provides a thumbnail sketch of Argelander's multitudinous life.

https://articles.adsabs.harvard.edu/pdf/1999JRASC..93...17C 

In 1923, Edwin Hubble's observations of a Cepheid variable, a special type of variable star, in the Andromeda galaxy was all the proof needed to demonstrate the vastness of the universe. This led to the birth of a new field of astronomy known as "cosmology."

Today, the American Association of Variable Star Observers (AAVSO) and related societies in other countries have continued to observe variable stars ever since Argelander's time. The AAVSO's observing sections touch on nearly every aspect of astronomy, to include pulsating stars, eclipsing binaries, young stellar objects, eruptive variables, gamma ray bursters, and exoplanets. In addition to photometry, the AAVSO even has a section devoted to stellar spectroscopy.

To learn more about variable stars and how to observe them, visit the web page of the AAVSO. Variable stars are a fascinating subject of observation and study by amateurs and professional astronomers alike.

https://www.aavso.org/

AAC Point of Contact for Variable Star Observing: Andy Howell