[TML] The Sky at Night?

[Jerry W Barrington]

On 12/5/07 8:32 PM, Patrik Holmstrom wrote:

> GT:First In for the most part (very nice but *hard* to find now)
> backed up by a couple of physics and astronomy books. I _think_ the
> new Gurps:Space have similar information but I don't have it so I
> can't say for sure.

Now that you've pointed me in good directions...  :)

First In's system looks a lot like Scouts, although it only has tables for
I, III, & V classes.  :(

G4:Space, on the other hand, determines the star's mass & age and works from
there.  It sticks to classes III, IV, & V.  A system with a lot of promise,
although the masses only go from .1 to 2.0 Solar masses (M7V thru A5V, and
the subgiants, giants, and white dwarfs these age to).  Granted, that
encompasses the vast majority of stars, but for completeness I'd like the
others too.

Having looked at these 2 books, I'll definitely have to refer back to them
again.

> Have you seen 
> <http://curriculum.calstatela.edu/courses/builders/lessons/less/les1/StarTable
> s_Z.html>?

I have now, and will *certainly* keep it bookmarked.  In fact, I now have
Web Devil sucking the whole course, for safety storage.  :D

An interesting issue that page makes explicit is that luminosity determines
temperature, but not directly visual brightness.



On 12/5/07 8:32 PM, Garry Ward wrote:

> In the section on mass & temperature, he has a formula I = (little dohicky
> for Stefan-Boltzmann) T^4.
> 
> Later, in the Luminosity section, he has a formula I = L / R^2.

Actually, the 1st formula would be the intensity of radiation per square
meter of surface.  The second formula shows that that intensity would have
to be multiplied by the area of the star (4 pi R^2 [R is radius of star in
meters]) to get the total luminosity.  It would be better rearranged as L =
I * R^2 [here R is in Solar radii].

All G2 stars have the same color, meaning the same temperature.  Luminosity
will then depend on radius.  All in Solar units: L = R^2 T^4 or
approximately = M^3.9.
<http://en.wikipedia.org/wiki/Luminosity>