Maps and charts of Helliconia, created by Brian W. Aldiss whilst writing his trilogy.
At the heart of Aldiss's trilogy is an idea that modern fans of fantasy may find familiar: a world where the seasons last not just three months, but years and even centuries. But unlike George R.R. Martin's A Song of Ice and Fire, the seasons of Helliconia are rooted in real scientific principles.
Helliconia is an Earth-like planet approximately 28% larger than Earth but with a more pronounced axial tilt of 35 degrees. This results in the planet having enormous icecaps which are larger than Earth's, but the planet nevertheless retains as much surface area as Earth, extending over three continents: the northern polar continent of Sibornal, the southern polar continent of Hespagorat and the equatorial continent of Campannlat, which is linked to Sibornal by a land bridge.
More important is the make-up of Helliconia's star system. Helliconia orbits at G4 star Batalix (an orange dwarf, somewhat smaller and less bright than our sun) at a distance of somewhat less than 1 AU (so Helliconia receives slightly less solar output than Earth). Batalix, in turn, orbits the A-class blue supergiant star Frey in a highly elliptical orbit. At apastron, the moment of greatest separation, Batalix is 710 AU from Freyr (for comparison, Pluto at its most distant from the Sun is still only 49 AU away); at periastron, the moment of minimal separation, Batalix is 236 AU from Freyr.
The orbits of Helliconia and Batalix around the star Freyr (not to scale).
It is revealed later in the novels that this arrangement is, relatively speaking, new: Batalix was captured by Freyr's gravity during a chance encounter eight million years ago. Prior to that time Helliconia was permanently a much colder world, and it was the capture that allowed humanity to evolve from an earlier primate species.
This push and pull of civilisation across millennia is echoed by a more personal threat: Helliconia is also home to a second sentient species. The phagors or ancipitals are a race of fur-covered creatures similar to mythical minotaurs. The phagors are optimised for life in the cold and are stronger and more formidable than humans in personal combat; however, they are (arguably) less intelligent and have never developed technology beyond that of the hunter-gather stage. During the Great Winters the phagors are the dominant species on Helliconia, whilst humans gain the upper hand during the Great Summers and force the phagors back to the polar continents.
Aldiss uses this ebb and flow of the seasons and species to drive his story. In each of the three novels in The Helliconia Trilogy (Helliconia Spring, Helliconia Summer, Helliconia Winter) Aldiss uses the change of seasons to chronicle the rise and fall of kingdoms, civilisation but, more important, individuals, who change, grow and learn from the ever-changing world around them.
A Song of Ice and Fire can clearly be seen as the fantasy equivalent of Helliconia. Scientifically and astronomically-minded fans have spent large amounts of time coming up with maps and charts of how the seasons might work in such a star system, sometimes drawing on dark matter or invisible neutron stars to explain the required orbital eccentricities. They are sadly doomed in such attempts, for there is no such scientific explanation: George R.R. Martin has been constant in his promise that the reasons for the long seasons of Westeros and Essos are magical, not scientific.
Still, they might take comfort that, fourteen years before Martin published A Game of Thrones, another author took on the same concept with a scientific viewpoint and delivered one of the greatest works of science fiction ever published. The influence of Helliconia on A Song of Ice and Fire is speculative - Martin has almost certainly read the series given its prominence but has never mentioned it to my knowledge - but certainly the parallels between the two series are fascinating.