So I'm walking across the parking lot at my local Home Depot this
afternoon and the sun is beaming down and it's generally a hot,
bright day.

Then I wonder what it would be like if this scene was taking place
on an Island 3.

Without looking at the horizon, would I be able to sense that I was
on a Habitat? Would I sense any centripetal force? Would the
sunlight be hotter or brighter on my face? Would I tan easier?

Here on Earth, the sunlight that reaches the ground goes through
many kilometers of atmosphere, smog, water vapor and is reduced in
intensity by the time it hits my face.

Will we let full strength sunlight into the Habitat or will we
filter it to lessen its intensity?

What do you think?

TangoMan

Without looking at the horizon, would I be able to sense that I was
on a Habitat? I would tend to think not. Would I sense any centripetal force? Should I assume you mean coriolis force? Again, in an Island 3 I would think not. Now as for an Island 1, I saw where somebody took a simple computer model of the buildings and streets of part of an urban area, and bent it through the curvature one would see there. The curvature was quite distinctive; more than I would have anticipated. I would say that even on a foggy day (or even inside the Home Depot), one would never mistake their surroundings for Earth, as the Home Depot would have a visually distinct curvature. But on an Island 3, the curvature would be much less and might not beparticularly noticeable at that scale. Would the
sunlight be hotter or brighter on my face? Would I tan easier? I've wondered if one would tan at all. I was thinking that glass was opaque to UV, but it seems like somebody let me know the situation was a bit more complex than that, and that some kinds of glass might let in some frequencies of UV. Here on Earth, the sunlight that reaches the ground goes through
many kilometers of atmosphere, smog, water vapor and is reduced in
intensity by the time it hits my face. In an Island 3, the sunlight would still be traveling through 4 miles of atmosphere. But in fact, with the mirror arrangement specified, whatever cloud cover existed you can multiply by 2, because the sunlight has to pass through 2 layers of clouds to get to you. But in fact, I'm not particularly convinced that the mirror arrangement we see in Island 3 will ever come to pass. Other mirror arrangements might not only be more practical, but might also avoid this particular peculiarity.

Regards,
Mike Combs

--- In ssi_list@... "Combs, Mike"

> Would I sense any centripetal force?
>
> Should I assume you mean coriolis force? Again, in an Island 3 I
would
> think not.
>

Yes, good catch.

> But in fact, I'm not particularly
> convinced that the mirror arrangement we see in Island 3 will ever
come to
> pass. Other mirror arrangements might not only be more practical,
but might
> also avoid this particular peculiarity.
>

Any thoughts on what these alternate mirror arrangements might be
for an Island 3?

TangoMan

Any thoughts on what these alternate mirror arrangements might be
for an Island 3? I think this habitat design is supposed to be a lot smaller than an Island 3, but I don't see any reason why it couldn't be scaled up to at least the same diameter(though not length): http://www.ssi.org/assets/images/Ch06p086.gif http://www.ssi.org/assets/images/Ch06p088.gif from: http://www.ssi.org/Don_Davis_Artshow.html

Regards,
Mike Combs

> Without looking at the horizon, would I be able to sense that I was
> on a Habitat? Would I sense any centripetal force? Would the
> sunlight be hotter or brighter on my face? Would I tan easier?
You would sense that you were in a habitat by moving vertically. As I calculated in an earlier post in the Coriolis thread, in an Island One I should feel a sideways tug equivalent to six pounds if I stood up rapidly from a chair. The Coriolis force scales linearly with the rotation, so since the Island Three of O'Neill's book has a quarter of the rotation rate of Island One, I should feel a sideways tug of about one or two pounds.
As for the sunlight, that is a matter of design: how large are the external mirrors, how opaque are the windows? How much cloud do we allow? That would partly be a matter of how much water there is in the habitat, partly on how swiftly the air is cycled through the radiators. Air cycled slowly through the radiators would have time to cool down significantly, causing a large percentage of the humidity to precipitate out, but simultaneously less warm, humid air would be extracted and less cool, dry air would be inserted. Larger mirrors combined with larger radiator surfaces would mean a larger temperature difference between the air being extracted from the habitat and that being inserted into it from the radiators, which again would likely mean less cloud, since more water would have been precipitated out. So there is room for weather design there. Similarly with allowing much sunlight into the habitat at daytime versus not so much, and cycling the air through the radiators more slowly at night, or more swiftly, for cooler nights. These things would influence cloud cover and aerosol content of the air, which again would influence how much direct sunlight shines on you. Remember also that clouds above the window areas of a Three would be sunlit from *below*, and you would see them from the sunlit side, particularly near the edge of a window. As well as the fact that the "sky" would have two bands of predominantly green, this would mean that light entering into a building through windows would have a different colour from what you might be used to on Earth, even if you weren't gazing out through the windows. But the effect may be too subtle to notice compared to different lighting conditions in different neighbourhoods in a single city on Earth.
Very likely the sunlight in a habitat will have less UV light, since any likely glass will tend to block that - or so I believe without knowing it. But any habitat designer would likely prefer to keep the UV light down, to reduce skin cancer among residents allowed to bask in the sun sixteen hours a day or whatever. Though perhaps some UV light would be permitted in - too little to increase significantly the risk of skin cancer, enough for such insects as can see UV light and use it to find flowers. But less UV light would mean less easy tanning.

> Here on Earth, the sunlight that reaches the ground goes through
> many kilometers of atmosphere, smog, water vapor and is reduced in
> intensity by the time it hits my face.
The atmosphere of the Earth is many hundred kilometers thick, but most of the mass is near the surface. The total mass of atmosphere above us is equivalent to ten meters of water. The total thickness of atmosphere above you in an Island Three would be the diameter of the cylinder - six kilometers. But the *mass* of atmosphere that the sunlight would pass through would not be that tiny a fraction - six divided by several hundred. A rough estimate would be this: water has approximately a thousand times the density of air, or somewhat less. So the ten meters of water corresponds to an atmospheric thickness of ten kilometers, or somewhat less, if the Earth's atmosphere were of constant density from the ground and up to some sort of ceiling.
The Island Three is six kilometers in diameter, and the atmospheric pressure at the axis, while not equal to that at the rim, is not significantly lower either. Three kilometers above ground level, it is at the pressure equivalent to one and a half kilometer's altitude on Earth. So the mass of air that a sunbeam will pass through in an Island Three would be lower than the mass of air that it passes through to the surface of the Earth, but not by an order of magnitude.

Jon Lennart Beck.

--- In ssi_list@... "Raven"

I enjoyed your thorough analysis of the question. As I was reading
through it I could visualize all of the dynamics involved. That got
me to thinking that you've really tapped into a budding discipline
of environmental engineering.

As each of the existing engineering disciplines embodies a deep well
of knowledge, so too will a body of knowledge be present in this new
one, where the dynamics of Habitat environments will be designed to
allow for cloud formation, types of clouds, atmospheric temperature
dynamics, wind origination points, scheduling of rainfall and on and
on.

Time to start building the theoretical models, don't you think?

TangoMan