On August 18, 1868, French astronomer Pierre Jules Janssen travelled to Guntoor, India, to observe a total solar eclipse. The 1868 eclipse and the mysterious yellow lineThe total solar eclipse gave astronomers a rare chance to study the Sun's prominences using spectroscopy. He developed what later became known as the prominence method, allowing astronomers to observe these structures without necessarily waiting for another total solar eclipse. The historical episode is particularly relevant as another total solar eclipse approaches Europe. As a result, a particular location can wait centuries before experiencing another total solar eclipse.