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Loading contentBeyond the Solar System lies a menagerie of clusters, nebulae, and galaxies. This encyclopedia gives that menagerie its taxonomy — the classes of deep-sky object, from open clusters to supernova remnants — and ties each class to the hundreds of real objects already mapped in the graph, so a nebula is never just a picture but a member of a family with a physical story.
The taxonomy of the deep sky — open and globular clusters and stellar associations, the emission, reflection, and dark nebulae, HII regions and Bok globules, planetary nebulae, and supernova remnants.
11 entriesIconic deep-sky objects added to the encyclopedia — the Horsehead and Cone nebulae.
2 entriesA small, dense, isolated cloud of cold gas and dust — a compact kind of dark nebula, named for Bart Bok — within which one or a few stars are collapsing into being. Bok globules are among the coldest objects in the Universe and are studied as the birthplaces of low-mass stars.
A dense cloud of interstellar dust so opaque that it blots out the light of the stars and glowing gas behind it, appearing as a dark silhouette. Catalogued systematically by E. E. Barnard, dark nebulae are the cold, dusty reservoirs — often molecular clouds — from which new stars condense.
A catch-all term for any object beyond the Solar System that is neither a single star nor a planet — the star clusters, nebulae, and galaxies that fill catalogues from Messier to the NGC. Deep-sky objects are the classic targets of the amateur telescope and the workhorses of stellar and galactic astrophysics.
A cloud of interstellar gas that glows with its own light, ionised by the ultraviolet radiation of nearby hot stars so that it re-emits in characteristic lines — most famously the red of hydrogen. Emission nebulae mark regions of active star formation and include the great HII regions of the Galaxy.
A dense, roughly spherical swarm of tens of thousands to millions of very old stars, tightly bound by gravity and orbiting in the halo of a galaxy. Globular clusters are among the oldest structures in the Universe, and their tightly packed, coeval stars make them benchmarks for stellar ages and the early history of the Galaxy.
A large cloud of ionised atomic hydrogen (H II) surrounding one or more hot O- and B-type stars, whose ultraviolet light strips the electrons from the surrounding gas. HII regions are the glowing signposts of massive-star formation, and their sizes and spectra are used to trace star formation across galaxies.
A loose, irregular group of a few dozen to a few thousand stars born together from the same molecular cloud, found in the disk of the Galaxy. Their stars share an age and composition, making open clusters key laboratories for stellar evolution; because they are only weakly bound, they gradually disperse over hundreds of millions of years.
The glowing shell of gas cast off by a dying Sun-like star as it becomes a white dwarf, ionised and lit up by the hot stellar core at its centre. Despite the name — coined because their round disks resembled planets in early telescopes — planetary nebulae have nothing to do with planets; they are a brief, beautiful final phase of low- and intermediate-mass stars.
A cloud of interstellar dust that shines not by its own emission but by scattering the light of nearby stars. Because fine dust scatters blue light most efficiently, reflection nebulae typically appear blue — as in the wisps of nebulosity draped around the Pleiades.
A loose grouping of young, massive stars that formed together but are not gravitationally bound, so they drift apart over tens of millions of years. OB associations trace the sites of recent star formation along a galaxy's spiral arms and are often still embedded in the gas of their parent clouds.
The expanding cloud of debris left behind when a star explodes as a supernova, sweeping up and shock-heating the surrounding interstellar medium. Supernova remnants seed the galaxy with heavy elements, accelerate cosmic rays, and — like the Crab — can harbour the neutron star born in the collapse.
A tall pillar of cold molecular gas and dust, about seven light-years long, sculpted by the radiation and winds of hot young stars in the NGC 2264 star-forming region in Monoceros. The Cone lies at the southern end of the same complex as the Christmas Tree Cluster, roughly 2,700 light-years away, and is a textbook example of a star-forming pillar.
One of the most recognisable dark nebulae in the sky — a column of cold, dusty gas in the Orion molecular cloud, about 1,500 light-years away, shaped by radiation into the silhouette of a horse's head. Catalogued as Barnard 33, it is seen against the soft red glow of the emission nebula IC 434 behind it, in the constellation Orion just south of the belt star Alnitak.
The objects, morphologies, and concepts these classes build on — reused, not duplicated.
Each entry is a first-class knowledge-graph entity resolved through the Scientific Data Engine, reusing the 600-plus deep-sky objects in the graph, the complete galaxy morphologies, the interstellar-medium concepts, the stellar-death processes and supernova classes, and the Messier, NGC, Sharpless and Barnard catalogues already present. Only well-established astrophysics is stated; distances and sizes appear only where firmly measured, and nothing is fabricated. See source quality.