''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 Tract may refer to: Geography and real estate * Housing tract, an area of land that is subdivided into smaller individual lots * Land lot or tract, a section of land * Census tract, a geographic region defined for the purpose of taking a census ...

comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...

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celestial object An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical object, physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''bod ...

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astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, natural satellite, moons, comets and galaxy, g ...

Giovanni Battista Hodierna Giovanni Battista Hodierna, also spelled as Odierna (April 13, 1597 – April 6, 1660) was an Italian astronomer at the court of Giulio Tomasi, Duke of Palma (Palma di Montechiaro). He compiled a catalogue of comets and other celestial object ...

published in 1654. It contains a catalogue of comets and other celestial objects, but had limited circulation and the work was forgotten until 1985. 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'').

Scope

The first part of his work (''De systemate orbis cometici'') followed Galileo's ideas on comets. The second part (''De admirandis coeli characteribus'') consisted of four main sections. The first concerns the classification of nebulaes. Hodierna classified the objects into three types according to their resolvability. ''Luminosae'', or star clusters to the naked eye, ''Nebulae'', or clusters that appeared nebulous to the naked eye, but which were resolvable in his telescope, and ''Occultae'', which did not resolve even with the aid of his telescope. The second part is a list of 40 nebulae, of which roughly 25 have been identified as known objects, the others having too unclear a description for a modern identification. The third section is an attempt at a unifying theory of celestial objects, and the fourth concerns

Copernican heliocentrism Copernican heliocentrism is the astronomical model developed by Nicolaus Copernicus and published in 1543. This model positioned the Sun at the center of the Universe, motionless, with Earth and the other planets orbiting around it in circular pa ...

Discoveries

Hodernia is credited with several first descriptions, discoveries and rediscoveries: These discoveries were part of an attempt at compiling a sky atlas, ''Il Cielo Stellato Diviso in 100 Mappe'', but the work was never completed.

Scope

Discoveries

References

Further reading