From: 103134.3516@compuserve.com   
      
   On Monday, October 9, 2017 at 1:19:45 PM UTC-4, Jack Bohn wrote:   
   > Paul Colquhoun wrote:   
   >    
   > > That's not the only difference. Ringworld is mind-bogglingly huge, with   
   > > the star located at the center, and shadow rings for day-night cycles.   
   > >    
   > > Orbitals are much smaller, down to single planet sized surface areas,   
   > > (or less) and orbit the star like a normal planet would.   
   > >    
   > > I can't remember how they did the day-night thing. Maybe shutters on an   
   > > enclosing roof structure?   
   >    
   > A brief look says that its spin is not in the plane of its orbit.  So, like   
   an inside-out planet, we'd see the sun rising and setting, but we are actually   
   turning towards and away from it.  I'm having trouble visualizing this; had to   
   sight along a ring-   
   shaped object towards a light to get some idea: the sun will be "going down"   
   all afternoon, but won't actually sink below the horizon, but go behind the   
   ring somewhere near it.  At the same time we will see in the east half the   
   ring lit, and that half    
   will rise and circle around the sky until the front of it meets the western   
   horizon, and the sun will peek out from around the ring in the east.    
   Actually, a lot of the lit ring will be visible in the sky in the mornings and   
   evenings.  It will be    
   brighter than the Moon per unit area because of the higher albedo and its   
   closeness.  We would see the sun to the north or south of where the ring would   
   be in the sky, except the equinoxes.  (I'm trying to work this out: the sun   
   appears to drift across    
   the fixed stars over the year, say one degree a day; the point where the   
   rotation of the ring crosses the ecliptic also drifts... at the same rate in   
   the opposite direction? so one edge of the ring should appear to cross the   
   half degree of the sun's face    
   in a quarter day?)  We know total eclipses, when natural and rare, cause   
   excitement.  I'm thinking two a year, especially when someone can be seen as   
   responsible for them, would be thought of as an annoyance.  So design the   
   orbital matching the thickness    
   to the radius such that it's visual size is half its sun's.  Noticeable, but   
   not disruptive.   
   >    
   > Which brings me to the question of what ignorant natives would make of the   
   shape of the world.  On Ringworld it was a table with an arch from which the   
   sun hung on a golden thread.  Here they might quickly work out that their arch   
   is closer than their    
   sun.  Also, being closer, the details on the rest of the ring would be   
   visible:  their far side might be as close as our Moon is.  How far around   
   would you have to go before you could look back and see the "map" of your home   
   there in the sky?  The view    
   of any close orbitals visible in the sky might give the answer right then.    
   (But why would an orbital fall into barbarism with others close?  Malevolence?)   
      
   Nicely reasoned, overall. But note that an orbital spinning for 1G of   
   psuedo-gravity with a day length of 24 hours has a diameter of about 2 million   
   miles (IIRC). So even if it's 20,000 miles wide (and therefore has surface   
   area equal to a thousand    
   earths) the far side of the ring won't eclipse the sun at all - rather, the   
   "eclipse" will reduce insolation only by a percent or so.   
      
   Interesting questions about what inclination to its orbit is appropriate for   
   an orbital's spin axis. I'm assuming the air is kept in by very high sidewalls   
   (like ringworld), or by a transparent roof.    
      
   If you have an inclination of 90 degrees, you'll have "seasons", including two   
   "winters" per year. The winters are when the spin axis points towards/away   
   from the sun. Even without sidewalls shading the surface, the sun angle is   
   zero degrees everywhere    
   in the orbital. It's cold!   
      
   If you have an inclination of zero, there are no seasons at all.   
      
   Somewhere in between you might get a nice seasonal variation (still with two   
   of each season per year). . .   
      
   JimboCat   
   --    
   "What did you bring that book that I didn't want to be read to out of up for?"    
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)