Re: Help with star catalogs requested


"ScottM" <scott@xxxxxxxxx> wrote in message
news:1133063494.173458.267760@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> This might belong in alt.astronomy, but glancing in there, I hope not.
>
> I'm looking for a set of information about visible stars that would be
> useful in a work of fiction, and I'm finding it slow going. I can find
> resources (like simbad) that can tell me that alpha Orionius is
> Spectral type M2Iab. What I really want to know is what color it would
> appear if you were on a hypothetical planet in the star's liquid-water
> zone, how long such a planet's year would be, if it's a multiple star
> system and how the other system members would appear to the naked eye,
> if the star pumps out anything that would make it especially nasty to
> live near, the metals content of the star relative to the Sun... that
> kind of stuff. Picture the details you'd want to see gotten right in
> reasonably hard sci fi, and you get the idea.
>
> I'm happy to derive my facts and I can write software to do any
> required calculations, but I haven't got a clue how to get from "type
> M2" to "red-orange, and a planet better be at least 10 au out if you
> don't want metals to boil on the surface."
>
> Pointers to more appropriate newsgroups welcome.
>

I can't help you that much, but here goes:

* Assuming the atmosphere is transparent, the colour you see on the planet
is the same colour as we see from Earth.

* You can work out how far the planet will be from its Sun if you know the
star's absolute magnitude. Each change of 1 in absolute magnitude is an
increase of a factor of 2.5 in light energy output. The amount hitting the
planet varies as the square of the distance, so being 1.0 greater absolute
magnitude than our Sun means the planet needs to be about 1.58 (sqrt(1*2.5))
times as far away. If its 2.0 greater, then it needs to be 2.23 times
further out (sqrt(2*2.5)), etc. Unfortunately, the period of the year will
also depend upon the mass of the star, which is mostly pretty speculative
(we can measure how bright a star is, and how far away, but until we find a
planet we cannot estimate mass). However, if you can find tables of the mass
of different stars, I can tell you the fomulas that you would need.

* be careful of multiple star systems. Not all potential systems allow
stable orbits for planets. You are probably OK if the planet closely orbits
one star, or is a Lagrangian system with two others. Generally speaking, you
can't have a planet in a stable orbit around two or more close binaries -
they get perturbed into chaotic orbits and eventually flung out of the
system.




.

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