(no subject)

[ewx]

Didn't make it to London on Friday night in the end owing to tiredness; but we had a nice evening in with Chinese food and Trainspotting which, despite having not watched for quite some time, I found myself remembering some of the dialog far too accurately. This is one of my favourite films, not just for its dark humour and liberal style but also the way it never quite lets you forget that Renton isn't in any absolute sense either very nice or particularly together; it is merely his (apparently) detached narration and the contrast with Begbie and Spud that make him look good in comparison.

More B5 on Saturday afternoon and then a trip to the pub in the evening. Despite feeling rather dopey towards the end of this I've since been completely unable to get to sleep, hence this rather late entry.

Before getting back up again I was wondering about some of the practical problems with Alderson discs. These are large discs with a hole in the middle and a sun in the hole; you play fast and loose with gravity and live on the flat surfaces. If you want day and night you bob the sun up and down; if you want seasons you move it in a circle around the axis of the disk with a period of 1 year (or an ellipse to vary the climate around the disk, perhaps?). But: to get the sun reasonably high in the sky - say, 45 degrees at noon - and a 24-hour cycle, you'd have to move the sun about 2AU in 12 hours, giving a mean speed of about 0.02c; the peak speed (dawn/sunset) would be higher.

The sun would thus be red-shifted in the morning and blue-shifted in the evening (though I'm not sure by how much), with a rapid transition through its 'true' color at the actual moment of sunrise/sunset.

Comments

[songster.livejournal.com]

The description of seasons makes little sense - they're mainly governed by sun angle rather than distance to the sun. You'd have to move the sun *way* off the axis to get anything like a normal seasonal effect - at UK latitudes the change in insolation from summer to winter is around two fold. That corresponds to moving it out from the axis around .3AU - which will be pretty nasty for those living at Venus-distance and will make no significant seasonal difference for those living at Mars distance. Any variation you do is going to be tuned only for one particular region of the disc, at which point you might just as well build a Ringworld and have done.

I'm also not convinced that raising the sun up to a higher angle is what you want to do - if you're at Earth distance and you raise the thing up 1AU out of the plane, you get 1/2 the insolation from it just due to the increased distance, though the higher insolation angle will affect that. Now that's going to play silly buggers with climate, to say the least. In fact, I suspect you can get your seasons more effectively by varying the amplitude of the sunset/sunrise, though again you'll find the effct is much more pronounced further in.

[ewx.livejournal.com]

Perhaps we can have a bigger sun or vary the radius we live at to get the right climate for the angle we want the noon sun at, and ridiculously large hubward mountains to provide some protection while the sun is close to the plane of the disc. Fair point about the seasons though.

[sobrique.livejournal.com]

It would make for pretty spectacular sunrises though...