On this day, in 1826, the Italian astronomer Giovanni Battista Donati was born. In 1864, he was the first to observe the decomposition of the light of a comet, that is, its spectrum. This observation allowed to conclude that the tail of a comet does not only reflect sunlight but also contains luminous gas. In 1858, he also discovered the comet now known as Donati's Comet. A lunar crater and an asteroid are also named after him.