Re: MotM: Nine Plate - day and night patterns

I absolutely love this moon. But like Stephen Hawking I have a brief question of time...

----- Original Message -----
From: "Night_Druid" <Night_Druid@??????????.net>
Subject: [SPELLJAMMER] MotM: Nine Plate, the Sandwich Moon

<snip>

> Day Length: 24 hours
> Year Length: 400 days

<snip>

> This moon appears as a stack of flat earth worlds, each 150 miles thick.
> Gaps of 150 miles separate each plate. The diameter of each plate increases
> from the poles to the equator, with the plate on the equator having the
> greatest diameter. Starting from the poles, the diameter of the plates are
> 500 miles, 1,000 miles, 1,500 miles, 2,000 miles, and finally 2,500 miles
> for the equatorial plate. This gives an overall appearance of a sphere.
> Enormous pillars join the plates, with the single largest pillar at the
> center, running from pole to pole.

<snip>

How do the days work on this planet? If the "poles" were tilted over slightly (like the
Earth) the sunlight would come onto them something like this:

North - South (Grainlund - Glachar)

    (-|-|-|-|-|-|-|-)

\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (sun rays)

(I've simplified the plates here - the middle ones should be much longer than the others
as they should have the same diameter as the length of the central pillar - please excuse
the poor quality ASCII art)

As you can see the top of Grainlund would be dark for 200 days and the bottom of Glachar
would be light for 200 days (like our Artic and Antarctic circles). The sunlight also hits
half of the "south facing" plates (the other half would be in shadow because the sunlight
would be blocked by the next plate). At first this looks like it gives you a 24 hour day
because as the planet rotates around the central pillar the dark parts of those plates
would rotate into the sunlight.

However this gives you a problem. The "north facing" plates don't get any sunlight at all
and won't get any until 200 days later (half a local year) when the sunlight will be
coming in from the north. Until then all their light would be indirect light bounced off
of the opposing plate.

After 200 days things would be reversed like this:

North - South (Grainlund - Glachar)

    (-|-|-|-|-|-|-|-)

/ / / / / / / / / / / / / / (sun rays)

You could instead say that the planet doesn't have any tilt, at all. Like this:

North - South (Grainlund - Glachar)

    (-|-|-|-|-|-|-|-)

| | | | | | | | | | | | | | | | |  (sun rays)

However with the light going straight through the middle I can't see any way that there
would be any shadow inside. This takes away your day and night.

:-(

The only solution I can see is to abandon the idea that Grainlund and Glachar are north
and south poles and instead make the moon tumble so that each one points to the sun in
turn over a period of 24 hours:

Grainlund - Glachar (midnight Grainlund time)

    (-|-|-|-|-|-|-|-)    <<<<<<<<<< (sun rays)

Grainlund (Glachar facing away from us) (6am Grainlund time)

           O            <<<<<<<<<< (sun rays)

Glachar - Grainlund (midday Grainlund time)

    (-|-|-|-|-|-|-|-)    <<<<<<<<<< (sun rays)

Glachar (Grainlund  facing away from us) (6pm Grainlund time)

           O            <<<<<<<<<< (sun rays)

I think this would work and would give every plate a 24 hour day for every day of the
year. However, it does give two problems:

1) The inner faces and outer faces of Grainlund and Glachar would be on opposite time
schedules (day on the outside/night on the inside and vice versa). This would possibly
have some sort of impact on the society that was 12 hours away from the other side of the
edge.

2) There would be some sort of eclipse everyday at noon. Even if you put the rotation of
the planet a little bit off centre there would still be some sort of shadow that would
last for a few hours.

Maybe you could write a bit more about this for a follow up article. It might be useful if
you could get someone to make a simple animation for Beyond the Moons when you get Static
to put this up. An animated gif that doesn't spin too fast would be a very good visual
aid.

I think that most non-spherical worlds and moons could do with visual aids to show how
their days work. I don't think people instinctively comprehend what light on something
like Nine Plate or Torus (from Practical Planetology) would be like. Is there anyone on
the list that would be able to make an animation of this (assuming Adam and Static want
one)?

David "Big Mac" Shepheard
Virtual Eclipse Role Playing Club
http://uk.groups.yahoo.com/group/virtualeclipselrp/links/d20_system_001071937434/Spelljammer_001071430476
http://virtualeclipse.aboho.com/