In 1868 French astronomer Pierre-Jules-César Janssen was studying a total solar eclipse in India with a device called a spectrograph. A spectrograph is used to figure out what something is made out of based off of the colors of light it gives off. The spectrograph uses a prism to split a beam of light into all of its different colors. Elements and molecules give off specific colors that are determined by how the electrons are bound to their host atom or molecule.
When Janssen pointed his spectrograph at the Sun’s corona he observed a signature that no one had ever seen before, a yellow line with a wavelength of 587.49 nanometers. Janssen called in the help of English chemist Edward Franklin, together they determined that the line belonged to a new element. They called it helium after helios, the sun god from greek mythology. This was the first time that an element was discovered in space before being discovered on Earth. Originally it was thought that helium only existed on the Sun. However, today we know that some does exist on Earth trapped in pockets underground. Due to its density, helium typically escapes our atmosphere very quickly.