It’s time to celebrate Helium, that noble gas, once again. Aug. 18, 1868: Helium Discovered During Total Solar Eclipse

French astronomer Pierre Jules César Janssen camped out in Guntoor, India, to watch as the moon passed in front of the sun and revealed the solar prominences. Like other sun-gazers that morning, Janssen discovered that the prominences were mostly made of super-hot hydrogen gas. But he also noticed something extra: Using a special prism instrument called a spectroscope, he determined that the line of yellow light everyone had assumed to be sodium didn’t match up to the wavelength of any known element.

We did this last year, too.