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]