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