Re-measuring Safehold

dobriennm wrote:Think you mean

• Circumference of planet: 25390.9 miles or 40892.7 km based on a downloaded map width of 9555 pixels and a scale bar length of 715 pixels (1900 mile/3060 km).
• Diameter of planet: 8,082.2 miles or 13,007 km based on circumference above.

My bad. I guess I was thinking of using a fraction of the circumference for a new Safehold mile and forgot to divide by π. Larger than Earth though, and it shouldn't be according to OAR. Need a better map to measure.

Dalton “still looking for all his marbles” Spence

Sorry, didn't mean to embarrass you. Actually, I think that was an impressive use of the available information.

I think the Author's problem is that the tools available to fans now are so much better than what was available 9 years ago when he started the series. and he puts out so much more information in readily available formats that we are able to do a lot of fact checking and, at times, nit-picking.

I suspect that if the Author was starting now, he'd be using software which would project his made up map onto a globe and use that for distances and projections. Of course, then he would still have the problem of trying to keep the software running on his computer system 9 years and two OS version or more later. Not an easy thing to do with niche software which is often developed/maintained by a small group or even just an individual. After all, can anyone think of some globe creation software available 10 years ago, easy to use, relatively fast running (on systems then) and still working with upgrades from Windows XP to Vista to Windows 7 to 8 to finally 10?

I'm more interested in the story than making absolutely sure that the details are completely correct

DaltonSpence wrote:
My bad. I guess I was thinking of using a fraction of the circumference for a new Safehold mile and forgot to divide by π. Larger than Earth though, and it shouldn't be according to OAR. Need a better map to measure.

Dalton “still looking for all his marbles” Spence

dobriennm wrote:Sorry, didn't mean to embarrass you. Actually, I think that was an impressive use of the available information.

Thanks. Okay, I’ve looked at the Celestia add-on file for Safehold “hip666665_v1-1.zip” and the “Safeholder's Not-So-Quick-Start Guide to Celestia_v1-0-7.txt” file by "Ensign Re-read" and got the following data:

SpectralType took some group participation before we found the quote specifying "G6".

The Magnitude is the 5th required value. This took some Q&A to get right.
The magnitude can be specified using either "AbsMag" (fixed brightness) or "AppMag" (apparent brightness as seen from the Earth).

AbsMag values smaller than 4.83 make a star brighter than the sun. Larger values make it dimmer. "1" is incredibly bright. (It's a logarithmic scale.) A value of about 4.9 or 5 probably would be reasonable.
I chose 5.0

Does anyone know the equation to convert magnitude into luminosity? I could use that to compute the planet’s black body temperature from a “SemiMajorAxis” of 0.90 AU and the mean surface temperature with 0.10 Albedo (both figures from the safehold.ssc file).

Since Earth has a radius of 6378.1 kilometers,
I've set the Safehold Raidus to
5740.29 Km because that is 90% of Earth's Radius.
Is there a "better" number available?

Well, is there? This gives a circumference of 36067.3 km or 22411.18 miles. Given it was stated in OAR that Safehold’s gravity was almost the same as Earth, its mass would be 0.81 Earth’s and its density 10/9 of Earth’s. Now if I only knew the moon’s (Langhorne) mass, I could calculate its orbital distance (I need the sum of both masses if the ratio of them is significant.)

The "Period", or time it takes Safehold to go around the Sun Kau-zhi, is:
0.824366872005476 (measured in T-years)
because: 301.1 / 365.25 = 0.824366872005476

The author apparently hadn’t read “A Note on Safehold Timekeeping” as of v1-0-7 but did correct the data for the v1-1 safehold.ssc file. A local day equals 1.10486 Terran ones thus a local year is 1.10486×301.32/365.25 = 0.91148 T-years (a bit more precise than in the safehold.ssc file). Using the formula M=D³/P² where M is the star’s mass in solar masses, D is the orbital distance in AU and P is the orbital period in Terran years, Kau-zhi has a mass of 0.877472 solar units. (Useful if we ever get data on the other planets in the system.)

Embedded within the value of "UniformRotation" is: "Inclination" 25.74
I've set the Axial Tilt (or UniformRotation > Inclination) to 25.74 degrees, because:
Earth has an Axial Tilt of 23.4 degrees.
25.74 degrees is equal to 23.4 x 1.1
Is there a "better" number?

<shrug> I don’t know one. That’s all for now. Now all I need is a ruling on how canonical the Celestia data is.
Dalton “who hopes Safehold isn’t ‘all alone in the night’” Spence

There isn't one. In fact, the data provided is too imprecise to be meaningful. For example, in what filter was that magnitude estimated?

Estimating luminosity requires, at a minimum, UBVRIZ photometry [or the equivalent data from another photometric system] of the star. Better is to also have UV data from Swift and at least Y, J, H & K photometry as well. Ideally, you also have at least one set of spectra covering the range from 100 to 25000nm - admittedly, data at the ends of that range is hard to come by, since time on Swift is harder to get than time on Hubble and we don't have any functioning sensors in orbit for the longer end. Given that, you can integrate the flux-calibrated spectral energy distribution and calculate the total [or bolometric] luminosity, which is the number you need. Every bit missing from that list means inserting assumptions about what the spectrum might look like, and those assumptions are in turn dependent on the age, metallicity, surface gravity [= mass & radius] and binarity of the star. Of those, I think we can safely say that Kau-zhi isn't a close binary, so we can ignore that factor.

BTW, all the calculated values you mention or quote are dependent on the assumption of .9au for the semi-major axis. Interestingly, that gives a stellar mass that seems to be more typical of G8 main-sequence stars than G6 [the relationship between mass and current spectral classification is less than exact even after age is accounted for]. This suggests that Kau-zhi, and therefore its planets, would be significantly older than the Sun, perhaps 2 billion years older, maybe more. That would certainly be consistent with the fact that despite what is obviously an extremely vigourous tectonic history, the place seems singularly devoid of active volcanoes.

DaltonSpence wrote:

SpectralType took some group participation before we found the quote specifying "G6".

The Magnitude is the 5th required value. This took some Q&A to get right.
The magnitude can be specified using either "AbsMag" (fixed brightness) or "AppMag" (apparent brightness as seen from the Earth).

AbsMag values smaller than 4.83 make a star brighter than the sun. Larger values make it dimmer. "1" is incredibly bright. (It's a logarithmic scale.) A value of about 4.9 or 5 probably would be reasonable.
I chose 5.0

Does anyone know the equation to convert magnitude into luminosity? I could use that to compute the planet’s black body temperature from a “SemiMajorAxis” of 0.90 AU and the mean surface temperature with 0.10 Albedo (both figures from the safehold.ssc file).

Louis R wrote:There isn't one. In fact, the data provided is too imprecise to be meaningful. For example, in what filter was that magnitude estimated?

...

BTW, all the calculated values you mention or quote are dependent on the assumption of .9au for the semi-major axis. Interestingly, that gives a stellar mass that seems to be more typical of G8 main-sequence stars than G6 [the relationship between mass and current spectral classification is less than exact even after age is accounted for]. This suggests that Kau-zhi, and therefore its planets, would be significantly older than the Sun, perhaps 2 billion years older, maybe more. That would certainly be consistent with the fact that despite what is obviously an extremely vigourous tectonic history, the place seems singularly devoid of active volcanoes.

That’s the semi-major axis I got from the Celestia data. It’s good to see it could explain some Safehold geology. According to my source (GURPS Space p.124 ) Sol is 4.7 billion years old, making the Kau-zhi system 6.7 billion. Oddly enough, the calculated mass of 0.877472 solar units is about half way between that of G6 and G8 in the “Stellar Evolution Table” from the same source (p.103). Is there any canonical astronomical data on the Kau-zhi system that I’ve missed? Planets, moons, asteroids, comets, anything? I want to try building the system using GURPS Space rules to fill the gaps, but I’d prefer to stick to canon where ever possible.

Dalton “more of a stats modeller than a gamer” Spence

The problem with tables like that is that they're static - and if you don't know what age is being assumed, they're pretty useless for a 'real' star.

Astrophysicists discuss the evolution of stars in terms of the Zero Age Main Sequence mass. That's because the spectral class changes as the star evolves - all stars move up the main sequence as they age, so a 1 M(sol) star could be anywhere between, roughly, G6 and F9, depending on how old it is. Extremely roughly, since i) I haven't taken the time to find a good evolutionary track and ii) in any case the evolution depends on metallicity. That's another property we don't know, BTW, although I'm going to stick my neck out and say that the density of Safehold indicates that it could be super-Solar.

Another thought that just hit me is that Safehold seems to have formed in the sweet spot of the habitable zone. Close enough to be in it on or soon after formation, far enough to stay in it as Kau-zhi gets hotter and brighter.

DaltonSpence wrote:That’s the semi-major axis I got from the Celestia data. It’s good to see it could explain some Safehold geology. According to my source (GURPS Space p.124 ) Sol is 4.7 billion years old, making the Kau-zhi system 6.7 billion. Oddly enough, the calculated mass of 0.877472 solar units is about half way between that of G6 and G8 in the “Stellar Evolution Table” from the same source (p.103). Is there any canonical astronomical data on the Kau-zhi system that I’ve missed? Planets, moons, asteroids, comets, anything? I want to try building the system using GURPS Space rules to fill the gaps, but I’d prefer to stick to canon where ever possible.

Dalton “more of a stats modeller than a gamer” Spence

Yup. If I had it to do again there are much better examples of mapping software available today than were available when I began mapping the planet. In fact, we are looking at the possibility of transitioning it to one of the more modern varieties. What I obviously can't do at this point is to start all over again in another system. There's so much detail on this map that trying to replicate it without a suitable transfer mechanism would be both a nightmare from a time perspective – I hate to think about how many hours I've put into this map as it stands – and bound to create an enormous number of errors.

This rather illustrates one of the problems with doing what I do for as long as I've done it. The real life universe continues to move forward, changing not only the tools currently available to a writer – like the new generations of mapping software – but also changing the basic starting assumptions available to him and his readers, alike. It's frequently true that an author who chose one set of starting assumptions 20 or 30 years ago would choose a different – or at least modified – set if he was launching the same series today. Unfortunately, he can't change them in an existing series, unless he wants to "cheat" both himself and his readership. Abrupt jogs in something that is essential to the story's foundations are simply unacceptable to a good storyteller. In my opinion, of course.

That's, frankly, even more true/apparent in the Honorverse than it is in this one, for some probably fairly obvious reasons. Unlike certain movie franchises, however, the author of a series of books can't do a "reboot" in which basic hardware or assumptions are abruptly changed half or 2/3 of the way through the series. So no matter how what's happening in the "real universe" affects a writer's understanding of the real/probable/possible trends or end destination implications of the technology he has or hasn't built into his books, he can't change the limitations/possibilities he assigned to the characters in them when he started. Technology can change and evolve, which happens quite a lot in my books, and new breakthroughs can occur, but the series' basic parameters can't, and neither can the starting point of his characters' technological gunny sack. Those are sort of locked in, and most discerning readers are (or certainly ought to be) more upset with authors who suddenly shift the conceptual ground under their feet and they are with authors who haven't hit the exact mark they think he should have when he set up his universe's underlying assumptions. I think that readers sometimes lose track of that particular limitation on literary universes. For that matter, I've seen instances in which authors rather obviously do the same thing!

dobriennm wrote:Sorry, didn't mean to embarrass you. Actually, I think that was an impressive use of the available information.

I think the Author's problem is that the tools available to fans now are so much better than what was available 9 years ago when he started the series. and he puts out so much more information in readily available formats that we are able to do a lot of fact checking and, at times, nit-picking.

I suspect that if the Author was starting now, he'd be using software which would project his made up map onto a globe and use that for distances and projections. Of course, then he would still have the problem of trying to keep the software running on his computer system 9 years and two OS version or more later. Not an easy thing to do with niche software which is often developed/maintained by a small group or even just an individual. After all, can anyone think of some globe creation software available 10 years ago, easy to use, relatively fast running (on systems then) and still working with upgrades from Windows XP to Vista to Windows 7 to 8 to finally 10?

I'm more interested in the story than making absolutely sure that the details are completely correct

DaltonSpence wrote:
My bad. I guess I was thinking of using a fraction of the circumference for a new Safehold mile and forgot to divide by π. Larger than Earth though, and it shouldn't be according to OAR. Need a better map to measure.

Dalton “still looking for all his marbles” Spence

runsforcelery wrote:Yup. If I had it to do again there are much better examples of mapping software available today than were available when I began mapping the planet. In fact, we are looking at the possibility of transitioning it to one of the more modern varieties. What I obviously can't do at this point is to start all over again in another system. There's so much detail on this map that trying to replicate it without a suitable transfer mechanism would be both a nightmare from a time perspective – I hate to think about how many hours I've put into this map as it stands – and bound to create an enormous number of errors.

You may have noticed from my other posts that I’m more interested in numbers than maps (although I did notice there were gaps on the western edge of the downloadable Safehold world map that break up the landmasses that cross that edge). While Safehold may be the setting of the story, it doesn’t exist in a vacuum. Well, technically it does, but that’s part of the problem you see. It exists in a vacuum with other planetary objects that we have heard nothing about. Planets, moons, comets, asteroids, all these things in Safehold’s skies may (hopefully) have no direct impact on the story, but for those of us who have come to love this world of yours information about them (even if only available online as a fake OWL data file) would make setting even more real. I don’t expect you to spend a great amount of time on this, but even something as simple as the number of planets in the system and Safehold’s position among them would help. Data about moons, asteroid belts, comets and gas giants would be gravy, as would info about the system's hyperlimit (if any).

runsforcelery wrote:This rather illustrates one of the problems with doing what I do for as long as I've done it. The real life universe continues to move forward, changing not only the tools currently available to a writer – like the new generations of mapping software – but also changing the basic starting assumptions available to him and his readers, alike. It's frequently true that an author who chose one set of starting assumptions 20 or 30 years ago would choose a different – or at least modified – set if he was launching the same series today. Unfortunately, he can't change them in an existing series, unless he wants to "cheat" both himself and his readership. Abrupt jogs in something that is essential to the story's foundations are simply unacceptable to a good storyteller. In my opinion, of course.

I guess this precludes discussion of my “Cher-ing the Moment" (aka “If I could turn back time...”) ideas. Too bad, I had some interesting thoughts on how to make 13 a Sacred Number (it requires adding two Archangels to the Heavenly Host covering new “spheres of influence”, establishing a clear “Heavenly Hierarchy”, changing Safehold clocks and calendars, and defining an official system of Weights and Measures for the Church based on a Divine Numerology ). Oh well, if anyone is interested in my “what might have been” fantasies, just PM me and I’ll share them.

Dalton “in the words of Number 5, ‘I need INPUT!’” Spence

Thank you, I like when you explain some of the limitations of the "authoring" process.

I wonder if some of the problems and limitations you describe below is the reason there are so few long running and complicated(?)/detailed(?) series. The amount of detail and the way assumptions set in the beginning can limit or constrain the story later may bog down an author so they literally can't move forward. (beyond the major problem of keeping those details straight)

runsforcelery wrote:Yup. If I had it to do again there are much better examples of mapping software available today than were available when I began mapping the planet.
..................
This rather illustrates one of the problems with doing what I do for as long as I've done it. The real life universe continues to move forward, changing not only the tools currently available to a writer – like the new generations of mapping software – but also changing the basic starting assumptions available to him and his readers, alike. It's frequently true that an author who chose one set of starting assumptions 20 or 30 years ago would choose a different – or at least modified – set if he was launching the same series today.
.....................
Technology can change and evolve, which happens quite a lot in my books, and new breakthroughs can occur, but the series' basic parameters can't, and neither can the starting point of his characters' technological gunny sack. Those are sort of locked in, and most discerning readers are (or certainly ought to be) more upset with authors who suddenly shift the conceptual ground under their feet and they are with authors who haven't hit the exact mark they think he should have when he set up his universe's underlying assumptions.

More canonical data about Safehold. From the first chapter of "Midst Toil and Tribulation;

Nor did he have to know he was nine thousand feet above sea level on a planet with an axial inclination eleven degrees greater and an average temperature seven degrees lower than a world called Earth, of which he had never heard.

From memory, Earth axial tilt is 23 degrees, making Safehold's 34 degrees. I'm not sure what Earth's current average temperature is (it's been changing lately, hasn't it) although I'm assuming the differential is in degrees Fahrenheit.

Dalton “re-reading the series to prep for the next book” Spence