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A Dyson sphere is a hypothetical megastructure first described in 1959 by the physicist Freeman Dyson in a short paper published in the journal Science entitled "Search for Artificial Stellar Sources of Infra-Red Radiation". It is an artificial hollow sphere of matter around a star designed to capture nearly all of the star's radiated energy for industrial use.Although Dyson is credited with being the first to formalize and popularize the concept of the Dyson sphere, Dyson himself got the idea in 1945 from a science fiction novel titled Star Maker by Olaf Stapledon. The original proposal by Dyson did not go into much detail about how a Dyson sphere would be constructed, focusing instead on the more fundamental issue of how an advanced civilization could expand its energy production to the maximum possible for a given solar system. Such a civilization would be classified as a Type II civilization under the Kardashev classification scheme developed by the astronomer Nikolai Kardashev.
1 Properties
A star contained within a Dyson sphere would not be directly visible to the outside universe, but the Dyson sphere itself would radiate an equivalent amount of energy in the form of infraredInfrared IR radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. The name means "below red" (from the Latin infra "below"), red being the color of visible light of longest wavelength. light due to solar heating from within. In addition, since Dyson spheres are composed of solid matter instead of heated gas, the emission spectrumA material's emission spectrum is the amount of electromagnetic radiation of each frequency it emits when it is heated (or more generally when it is excited). The term often refers to the visible light emission spectrum, although it extends to the whole e of the Dyson sphere would more closely resemble a black body spectrum than the typical emission spectrum of a star, which has absorption features introduced in the stellar atmosphereDifferent stars have different atmospheres. All stars possess a so-called photosphere, which is the lowest and coolest part of the star's atmosphere and as the photosphere is the part which we see with our eyes (hence the name) you can think of it as the. Dyson proposed that astronomers search for such giant anomalous "stars" in order to detect advanced alien civilizationsExtraterrestrial life refers to theoretical forms of life that may exist and originate outside of the planet Earth. Forms of extraterrestrial life, or "life on other planets", range from the humanoid and monstrous beings like those from science fiction wo, but none have been recorded. Attempts to detect Dyson Spheres using the IRASThe Infrared Astronomical Satellite IRAS was a space-based observatory that performed a survey of the entire sky at infrared wavelengths. Infrared Astronomical Satellite (IRAS Organization NASA, NIVR, SERC Wavelength regime infrared Orbit("sun-synchronous ( Infrared Astronomical Satellite) sky survey data are currently underway.
Shell-type Dyson spheres are neutrally stable, having no apparent overall gravitational attraction toward the enclosed star (in contrast to a ringworldRingworld is the title of a 1970 science fiction novel by Larry Niven, set in his Known Space universe. The work is widely considered one of the classics of science fiction literature. It is followed by three sequels, and it ties in to numerous other book, which is much more unstable). Thus the sphere would only need propulsion to counteract any unusual forces moving it out of place relative to its star.
2 Varieties
There are several basic varieties of hypothetical design for a Dyson sphere.
2.1 Swarm
The most realistic of them, and the closest to Dyson's original conception, is the "Dyson swarm". It consists of a large number of independent solar collectors orbiting in a dense formation around the star. The solar collectors could range widely in individual size and design, and possibly include space habitats for biological creatures to live in, but as a group they would collectively intercept almost all of the star's total light output. A number of different orbital patterns for the collectors have been proposed, each with different benefits and drawbacks; whatever pattern is chosen, some solar collectors will spend part of their orbits in the shadows of other solar collectors, reducing the sphere's efficiency somewhat. Since the collectors operate largely independent of each other, a Dyson swarm can be constructed incrementally over a long period of time and provide useful output throughout.
