De systemate orbis cometici, deque admirandis coeli characteribus

De systemate orbis cometici, deque admirandis coeli characteribus (transl. Of the systematics of the world of comets, and on the admirable objects of the sky) is a small tract on comets and other celestial objects by the Sicilian astronomer Giovanni Battista Hodierna published in 1654.^[1] It contains a catalogue of comets and other celestial objects, but had limited circulation and the work was forgotten until 1985.^[1][2] In this work, Hodierna expressed the belief that comets were made of a more terrestrial substance, and considered nebulae to be made up of stars (Lux Primogenita).^[1][2]