In the early 1800s, physicist Joseph Fraunhofer used an early spectroscope to observe the sun and noticed black lines interrupting its spectrum, which he did not understand.
Sources
- How Scientists Discovered Helium, the First Alien Element, 150 Years Ago (smithsonianmag.com)
- https://www.fraunhofer.de/en/about-fraunhofer/profile-structure/chronicles/joseph-von-fraunhofer.html (fraunhofer.de)
- https://www.aip.org/library/ex-libris-universum/here-comes-the-sun-historical-instruments-for-solar-observation (aip.org)
- https://www.atnf.csiro.au/resources/education/senior-astrophysics/spectroscopy/spectro-history/ (atnf.csiro.au)
- https://www.ebsco.com/research-starters/history/fraunhofer-invents-spectroscope/ (ebsco.com)
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