The diaphenous nature of giant stars

[Carlobrand]

Have we discussed judging jump shadow by setting some arbitrary lower matter density limit on shadow influence?

Terrestrial density runs in the 3 to 6 grams per cc range. Terrestrial jump shadows are 100 diameters, presumably judged from the world surface.

Jovian gas giants - at least the ones we can measure with reasonable accuracy - run from 0.687 to 1.64. That's in the range of air [oopsie; that should be water] density. They're considered to have 100 diameter shadows as well, presumably measured from the "top" of their appreciable atmospheres.

The sun runs to 1.4 grams per cc, with the photosphere layer ranging from 0.2 to 2 x 10-4 grams per cc. We're saying it also runs a 100 diameter shadow - and fiddling about density doesn't help much 'cause the layer of "thin" stuff isn't all that deep; it gets reasonably dense pretty fast

The giant stars though, those peskersome titans, are little more than a huge envelope of thin brightly glowing vapor surrounding a denser burning core. Betelgeuse is around a thousand times the size but a hundred-millionth the density of the sun - much of the star about the density of Earth's atmosphere 100 km up. Mind you, that's still about 8 orders of magnitude denser than a good dense interstellar gas cloud but, yes, you could fly your ship through the outermost reaches of a giant star with relatively little drag. It's about as much stuff as our lowest satellites face - it's just very, very warm.

However, it's presently enough to make reaching Narsil or Menorb a major headache.

So, the question: can we get some relief from the big star jump shadow problem if we were to say that matter had to reach a certain density level before throwing a jump shadow that would cause an effect on jump? If we rather arbitrarily declare that you have to achieve a density of, say, a millionth of a gram per cc (10-6) in order to be able to throw a jump shadow, would we then be able to sit down and recalculate a Betelgeusian jump shadow to something less destructive to interstellar trade? Or is the math too ridiculous to be able to guesstimate how "high" in Betelgeuse you go before you reach that magic density?

Or could we just set an unstated density and then introduce some curve on that basis that allows the jump shadow calculation to trend down from 100 diameters for a main class star to (arbitrarily) 20 diameters for an M class bright giant?

 

[Vladika]

Have we discussed judging jump shadow by setting some arbitrary lower matter density limit on shadow influence?

Terrestrial density runs in the 3 to 6 grams per cc range. Terrestrial jump shadows are 100 diameters, presumably judged from the world surface.

Jovian gas giants - at least the ones we can measure with reasonable accuracy - run from 0.687 to 1.64. That's in the range of air [oopsie; that should be water] density. They're considered to have 100 diameter shadows as well, presumably measured from the "top" of their appreciable atmospheres.

The sun runs to 1.4 grams per cc, with the photosphere layer ranging from 0.2 to 2 x 10-4 grams per cc. We're saying it also runs a 100 diameter shadow - and fiddling about density doesn't help much 'cause the layer of "thin" stuff isn't all that deep; it gets reasonably dense pretty fast

The giant stars though, those peskersome titans, are little more than a huge envelope of thin brightly glowing vapor surrounding a denser burning core. Betelgeuse is around a thousand times the size but a hundred-millionth the density of the sun - much of the star about the density of Earth's atmosphere 100 km up. Mind you, that's still about 8 orders of magnitude denser than a good dense interstellar gas cloud but, yes, you could fly your ship through the outermost reaches of a giant star with relatively little drag. It's about as much stuff as our lowest satellites face - it's just very, very warm.

However, it's presently enough to make reaching Narsil or Menorb a major headache.

So, the question: can we get some relief from the big star jump shadow problem if we were to say that matter had to reach a certain density level before throwing a jump shadow that would cause an effect on jump? If we rather arbitrarily declare that you have to achieve a density of, say, a millionth of a gram per cc (10-6) in order to be able to throw a jump shadow, would we then be able to sit down and recalculate a Betelgeusian jump shadow to something less destructive to interstellar trade? Or is the math too ridiculous to be able to guesstimate how "high" in Betelgeuse you go before you reach that magic density?

Or could we just set an unstated density and then introduce some curve on that basis that allows the jump shadow calculation to trend down from 100 diameters for a main class star to (arbitrarily) 20 diameters for an M class bright giant?

I like, and would go with, any of your suggested "fixes". We've been told all along that the 100d rule was due to gravity. IF that is true, and still a held view, then by all means let's treat it so!

If PCs are to lazy to do the math, let them continue to jump from 100d. Of course that might not work real well either in some cases

 

[tjoneslo]

After several loops around this problem on the TML, I've adopted the idea of tidal force measurement to determine where the "100D limit" exists.

I calculated the tidal forces of a normal rocky planet at 100D radius and used that as a baseline. For other rocky worlds the "safe" radius calculated somewhere between 80 and 110 diameters depending upon planetary density. For Gas Giants you ended up with safe radius at around 40-60 diameters. For some of the larger stars, the safe radius ends up being inside the stellar envelope.

I like this because it makes sense to my science mind, and makes it easy to determine the safe jump distance from other oddities like stellar nebula, the core of the galaxy (charted space is within 100 diameters of the galactic core), black holes, other space ships, and so on.

Tidal force measurement is 2GM/R^3. If I recall from my now lost spreadsheet, I was using something around 1E-6 as the calculated safe tidal force.

 

[Carlobrand]

Aramis linked to someone's post about the idea in another thread. It's an interesting idea. I couldn't figure out why the use of the cube instead of the square, though it works well. My physics is weak.

 

[aramis]

Aramis linked to someone's post about the idea in another thread. It's an interesting idea. I couldn't figure out why the use of the cube instead of the square, though it works well. My physics is weak.

Because tidal force (the function of the difference of acceleration of a body of a given length) drops off by a cube of the distance, rather than the square.

If at distance D, a body of lenth L experiences 2mm/s² tidal stress (that is, the inside edge experiences 2mm/s² more gravitational accelleration than the outside edge), then at distance 2D, it will experience 0.25mm/s² tidal stress.

One other thing fun about tidal stress: if the object is in orbit, the tidal stress will feel half as strong, but will feel like acceleration to the nearest end, with microgravity at the center of mass.

I can't remember the exact formulae for it, but Peter put it in his web article.

 

[McPerth]

For some of the larger stars, the safe radius ends up being inside the stellar envelope.

I like the idea, but I'd also rule that the jump/arrival point to be outside any atmosphere to be safe (in the case of jump, as arrival is just not posible), jsut to avoid that (or some place where it will end inside the body's atmosphere, as it surely will happen in some cases).

 

[Carlobrand]

Because tidal force (the function of the difference of acceleration of a body of a given length) drops off by a cube of the distance, rather than the square.

If at distance D, a body of lenth L experiences 2mm/s² tidal stress (that is, the inside edge experiences 2mm/s² more gravitational accelleration than the outside edge), then at distance 2D, it will experience 0.25mm/s² tidal stress.

One other thing fun about tidal stress: if the object is in orbit, the tidal stress will feel half as strong, but will feel like acceleration to the nearest end, with microgravity at the center of mass.

I can't remember the exact formulae for it, but Peter put it in his web article.

That makes sense. I did mention my physics was weak. So it's less a force-at-any-give-point thing and more a stretchy-space thing. I like that. It's the best explanation I've heard to date.

I gotta do some math, but I think that sets a lower limit of mass to the effect, which would mean ships shouldn't exert the effect.