Is there a definition for Orbit(al) Factor?

[manhamster]

This is shown in the World Builder's Handbook ( pg. 64; 3b ), but there is no explanation on what the numbers represent. I have looked in various spots but so far can nothing really that delves into the subject too much. It looks so much like the results of a formula that it has piqued my curiosity.

Is there a unofficial or official definition for Orbit(al) Factor?

 

[GypsyComet]

That number represents the relative amount of solar radiation falling per a given area of planetary surface at each orbital distance, cooked a bit further to fit into the rest of the numbers to give a useful Kelvin value. I haven't crunched the numbers myself, but they likely follow the Inverse-Square law for radiation from a point source.

 

[manhamster]

I am not sold on the Inverse-Square law being used, just because so far I have not seen any formulas with results in the ballpark to those for the orbit factor. The orbital distances listed on page 62 are pretty close to what NASA has for the distances for the various planets; so I taken that as a clue that it drawing from other solar system data.

 

[GypsyComet]

That's what it *should* be. But I just crunched the numbers. Apparently "Inverse Square" meant "Square Root" in DGP Land. The numbers in that table are inversely proportional to the square root of the standard orbital distances.

 

[manhamster]

Would you be willing to walk through an example or two?

The Inverse-square that keeps coming to my mind is the one for Insolation/Sunlight. Any idea what units of measurement DGP used for calculating these numbers?

 

[GypsyComet]

Use the orbital radii on Page 62, Table 7b
Take the square root of those AU values
take the inverse of that
Multiply the result by 374.025

So: O=374.025/SQRT(r)

That produces the values on Page 64, Table 3b

Is it science? Probably not.

 

[manhamster]

Ah, interesting. I recognize that number, Book 6 ( CT ) lists it as the Average Temperature for Earth.

I agree, I do not think I have seen a formula like that, though it is interesting concept in it's own way.

 

[Carlobrand]

The formula they used in Book 6 was:

T=KG(1-A)(L^0.25)/D^0.5
where:
L= Luminosity in solar units.
A= Albedo for the world (ranging from 0.01 to 0.99).
D= Distance from the primary in AU.
T= Temperature in degrees Kelvin.
G= Greenhouse effect.
K= 374.025.

If you eliminate all the world-specific stuff like albedo and greenhouse effect and assume L to be 1, you end up with:
T=K/D^0.5

That does seem to generate those numbers, when you measure D in AU.

 

[GypsyComet]

That does seem to generate those numbers, when you measure D in AU.

So this goes back to Book 6. I can't blame DGP for it, then.

Regardless of what units you use for orbital radius, the ratio from Orbit 0 to 19 follows that table. The result is that Traveller outer worlds don't cool off as fast as they probably should. That's not to say they don't get really cold.
The other effect is that the habitable zone may shift incorrectly with changing stellar conditions. While I would not normally worry about it, the chance that we might be able to get the Trappist system to work right in Traveller is a temptation.

 

[robject]

I remember doing something like this on a simplified scale...

 

[Ishmael]

The formula they used in Book 6 was:

T=KG(1-A)(L^0.25)/D^0.5
where:
L= Luminosity in solar units.
A= Albedo for the world (ranging from 0.01 to 0.99).
D= Distance from the primary in AU.
T= Temperature in degrees Kelvin.
G= Greenhouse effect.
K= 374.025.

If you eliminate all the world-specific stuff like albedo and greenhouse effect and assume L to be 1, you end up with:

T=K/D^0.5

That does seem to generate those numbers, when you measure D in AU.

The (1-a) should also be a forth root. This will also change the 374.025 to another value as well. As a result WBH is also incorrect.

https://scied.ucar.edu/planetary-energy-balance-temperature-calculate