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The Ringworld
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If our solar system had been used to create the Ringworld then everything would have been used for it's manufacture.  No planets, asteroid belt, gas planets or comets would be left behind.  In fact to make the Ring the material from nearby solar systems would probably have to be brought to add material to the project.

At the orbit of Earth would be, instead, a ring with an internal surface that is 997,000 miles wide, about 125 Earth-diameters!  The whole inner surface of the ring would provide the surface are of 3 million Earths.  The size of this thing is almost inconceivable.  The ring is spun at a speed to provide 1G of gravity on the innerside (that of Earth).  At the orbit of Mercury there would be 20 giant shadow squares sufficient in width to occlude the Sun enough so that a shadow can be cast on the inside of the Ringworld - to provide night.

In the Ringworld in the game, the Ring is set at 95 million miles (152.9 million Km) from it's G3V (a main sequence dwarf) sun.  Star EC-1752 has been chosen and sits somewhere in the constellation of Coma Berenices if you were to try and view it from Earth.    The ring is spun at 770 miles per second  (1239km/sec), completing one revoluion in 9 United Nation Standard days (24 hours x 9).  The night lasts for 9 UNS hours and the day is 21 UNS hours, giving a 30 hour day.

The Ringworld is home to some 30 trillion sentient inhabitants from up to 2000 Hominid Species.

The Ringworld From Space

Below is an excerpt from the players handout in the Ringworld RPG which describes what the ringworld would look like as you approach it in a starship.  To see what it might look like from space go here.

"The Ringworld sun is a solar-type star, a shade less intense than Earth's own.  From anywhere in Known Space it is several magnitudes too faint to see with the unaided eye.  Through a telescope it looks like a pefectly ordinary example of the thousands of yellow dwarf stars within several hundred light years of Sol. Careful spectroscopic studies might reveal periodic magnetic anomalies and occasional intense flare activity; and extremely precise astrometric measurements might suggest the absence of any major planetary family, but that is about all.   The plane of the ring is face-on to Human Space, so the disk of the star cannot be even partially occluded."

"From the edge of the Ringworld system, the G3 sun is nothing more than a blazing white point - but with a difference: this star wears a barely-visible halo.  At a distance comparable to the gulf separating earth from Pluto, Ringworld is already a naked-eye object, a shallow pencil-line of arc-blue with its sun nestled serenely at the centre.  As you decelerate into the system at 30gees, the Ring shifts its position gradually, too slowly - evidently its diameter is huge, though in proportion it is thin and narrow, not much wider across than its star at its axis.  Ringworld is a band of solid material, clearly an artifact.  Its near side is a dim dead-black line occulting a few stars, sharp-edged were it cuts across the solar disk.  The further side is a pale blue ribbon across space, with long streaks of glowing baby-blue interrupted by shorter strips of deep midnight blue.  The surface looks as if it has been laid out in a series of regular, rectangular dots and dashes.  There are no other objects visible on the way in - no planets, no asteroids, no periodic comets or meteoroid swarms, no interplanetary craft or space stations."

"Much closer to the Ringworld, major details become discernable, first through telescopes and finally to the unaided eye as the structure looms near.  The blue daylit rectangles of the Ring develop a complex, finely-etched textured appearance at the limit of resolution, overlain with thin smudges of indistinct white cloud-cover. Faintly deeper-blue areas which might be land masses are intricately intertwined  with patches of lighter blue which might be seas.  Occasionally there is an unusual spot of brightness, like sunlight reflected from an ice field, a polished metal plate, or the surface of a calm ocean at just the right angle.  The two Great Oceans can be picked out easily, if you look for them, 180° apart around he checkered surface of the Ring.  One is oval in shape, the other a ragged four pointed star.  The shadowed regions are quite visible, blue-black with blurred straight edges for boundaries, containing a hint of differentiated shading.  And a ring of 20 dark, retangular outlines circle near to the Ringworld sun, like a swarm of huge black moths."

"From a dim, sharply-defined line, the rim of Ringworld slowly grows by degrees, to a featureless straight black wall 1600km [1000miles] high.  The rotational velocity of the Ring is by now obtrusively apparent, requiring five gees acceleratoin to hold a constant curved path next to the wall.  Close to the rim wall, or to the underside of the structure, half the sky seems a dark geometric abstraction, its edges converging to vanishing points at either end of th euniverse.  From two of the points at infinity, narrow lines of baby-blue and midnight shoot straight upward.  If you have picked the right spot on th rim, you may glimpse 160-km-diameter toroids, spaceport ledges (perhaps with intact craft), towers plainly for attitude jets, or (just as you maneuvar over the top edge of the rim wall) the rectangular loops of a transport system.  From this vantage point, 1600 km above the Ring floor, no other signs of civilization are visible.  Barely discernale are the curiously regularly spaced, half conical bumps of nearly 50-km-high mountains far below, leaning against the base of the rim wall."

"The Panorama unfolds in breath-taking detail as you descend slowly toward the upper reaches of Ringworld's atmosphere.  The Ring becomes a luminous parabolic arch above, and you lose all track of how the rim walls and Ring floor merge together as a single circular artifact.  Below, rapidly expanding, all the surfaces of all the earthlike worlds in a dozen galaxies seem to be spread out flat for beholding.  Swirled white cloud-decks resolve first, some right enough to dazzle the eyes, in soft blankets and churning storms, in long parallel streamers, and in diminutive, dappled wooly fleece.  Topography appears: continents and oceans, huge mountain chains, lakes, valleys, patterns of rivers and streams, endless flat plains, barren deserts, vast forests, snow fields, and odd patches of regularly textured land or dully gleaming spots that look disturbingly unnatural.  The surface area is more than 50% water, with an endless sprinkling of small shallow seas and large oceans, evenly distributed but scattered at seeming random.  Their exotically convoluted shorlines display a striking variety of gulfs, bays inlets, peninsulas, river deltas, natural harbors, and wide sandy beaches; while island archipelagos dot their faces.  Sluggish, silt-laden rivers and extensive marshlands are visible, as well as colorful jungles and lush tropical rainforests.  With a surface area three million times that of Earth, there is room enough for everything.  It is easy for a traveler to lose perspective, to forget the scale of the artifact, and to habitually underestimate sizes and distances amid such a landscape.  It is quite dificult to recall that the stunning variety and geographic splendor that is Ringworld did not evolve naturally - and even harder to understand that every topographic detail and major feeature had to be carefully planned, meticulously designed, and molded in bas-relief in the ultrasolid foundation material."

©Steven Vincent Johnson, you are looking spinward, as a night/day terminator approaches.  Each Ringworld day lasts for about 30 UNS hours, 9 hours of which is the Ringworld night - a shadow cast on the innerside of the Ringworld by a shadow square. There is a ring of 20 shadow squares connected by incredibly strong black monofilimanent shadow wire. This ring of squares is spinning antispinward (opposit to the spin of the Ringworld) around the Ringworld star.  Each shadow square revolves around the star with a period of 11.4 Ringworld days (14.2 UNS days).  Each shadow square is about 9.66 million Km apart and has dimensions of 1.6 million by 4.18 million km.