A compromise between a normal planet and a Dyson
sphere. A ringworld would be an artificial, band-shaped structure placed
around a star within the star's habitable zone.
Although, unlike a Dyson sphere, it would intercept only a small fraction
of the total radiation output of the star, the incident energy would still
be many millions of times greater than that falling on a planet. The ringworld
would be easier to build than a Dyson sphere, allow freer access to open
space, and be completely habitable (in contrast with most of the interior
surface of a Dyson sphere which would be subject to reduced gravity conditions.)
As a bonus, those living on a ringworld would be able to see the stars.
Larry Niven speculated about such a structure
in his novels Ringworld and The
See also Richard Cathcart's essay