The only caveat to the above I can think of is that having that kind of technology to build completely self-sufficient and mobile colonies would also mean that we would have no need for earth like planets at all, just raw materials in space to make more colonies, and thus would not have as much incentive to make such journeys in the first place.

Also, if the trip is sufficiently long, the population of the colony could diverge evolutionarily and perhaps wouldn’t be considered human any more, at least not by today’s admittedly limited standards.

My source for Vega’s mass was James B. Kaler’s book – ‘The 100 Greatest Stars’ – it does seem low esp. given Vega is often described as quite blueish … But Kaler is the expert in this area so .. interesting,. estimates can vary certainly.

“White dwarfs” would seem confusing to me given the application to both white dwarf stars (about 1 to 1 & 1/2 solar masses jammed down into roughly earth-sized spheres) which are stellar remmants – the old cores of medium mass stars and (about 2 solaramss, many times the solar diameter) A0-type main sequence stars. By the logic above both Sirius A & Sirius B would be white dwarfs yet they are VERY different types of star! Same for F-type yellow-white hence using Sirian & Procyonese to avoid that possible confusion …

O/B – blue
A – white
F – yellow-white
G – yellow
K – orange
M – red

But for A-type stars and hotter the dwarfs/giants distinction becomes rather less clear or useful, plus even main sequence (”dwarf”) stars are getting pretty big by this point. The term “blue dwarfs” seems to more often refer to a type of galaxy rather than a type of star. Main sequence stars of spectral type A are “white main sequence stars” I guess.

Furthermore these colours are rather approximate, and set up relative to Vega (an A0 star). If you choose your colour system so that sunlight is “white”, M and K are orangey-pink, G is white, F is whitish with a hint of blue, and A onwards get progressively bluer.

Regarding the mass of Vega, you seem to have found a source giving a rather low estimate – the usual figures I’ve seen are somewhere in the region of 2.5 solar masses: SolStation gives 2.3-3.1 solar masses.

As for “red giants”, yes this term does include types K and M. As far as I can tell, there are as yet no known exoplanets around M giants.

Sandy.

Sirius A spectral type = A1 mass “about twice” our Suns, its luminosity is 23 times our Sun’s and its surface temp 9400 degrees Kelvin.

Sirius B (”the Pup” to “the Dogstar”) is an archetypal DA hydrogen-rich white dwarf is about as massive as our Sun – but considerably smaller, (Earth-sized) fainter and hotter.

Fomal haut is an A3 star and thus similar to Sirius but a fraction less massive, smaller and cooler.

Contradictadorily enough, Vega is an A0 type Sirian* dwarf star but confusingly is listed as being only 1.5 times the solar mass yet 54 times as bright versus the respective figures for Sirius A …

(Sources : James B. Kaler, “The 100 Greatest Stars”, Copernicus Books, 2002 & ‘Astronomy’ magazine Stars poster April 2006.)

Incidentally, not to be too pedantic but shouldn’t we call these red giants ORANGE giants instead seeing they are K-type stars?

Surely : O type main-sequence stars = blue dwarfs
B type ” ” ” ” ” = blue-white dwarfs (or just blue?)
A type ” ” ” ” ” = Sirian* dwarfs
F type ” ” ” ” ” = Procyonese* dwarfs
G type ” ” ” ” ” = yellow dwarfs (or solar?)
K type ” ” ” ” ” = orange dwarfs
M type ” ” ” ” ” = red dwarfs

with the same rule applying for giants & supergiants as for dwarfs … ?

Therefore surely the K type Pollux, Aldebaran, Arcturus, etc Plus HD 17092 are actually all Orange rather than Red giants – a shade off but still .. Or do K & M giants just get lumped together as red regardless of spectral colour type?

—————————

‘Sirian’ = main sequence A type dwarf star as calling these stars “white dwarfs” risks confusing them with the very different type of stars -or rather ex-stars such as Sirius _B_ . Ditto “Procyonese”

Seems similar to Pollux’s exoplanet “Polydeuces” * … that had a 590 day orbit (3 Jove mass) which I’d mis-calculatedas putting it between Mars & Earth distance based on exactly the “Earth-like orbit error” discussed here. D’oh!

Fomalhaut is type A3, Sirius A1-0 (?) from top of head.

Thought Sirius was twice solar mass but could be 2 & 1/2.

So if the latter tehngoing by what was written earlier Aldebarran used tobe (during its main-sequence H-burning lifespan) a star like Sirius (well Sirisu A that is!)

Cool – thanks for that info. (mass Aldebarran etc ..)

———————————————————

* Polydeuces -alternate name for Pollux, mythological Greek form

However, I expect if we start building large numbers of space colonies, we’ll be kept way too busy playing in our own solar system to be settling other solar systems, at least in the near term(read 10,000 years or so) and what kind of tech we’ll have by then is anyones guess. I really expect, if the space colony with fusion power is adequately developed, we’ll have settlers in the Oort clouds all the way to the nearer stars, long before we have any need for FTL.
Last I heard, the Oort clouds extend nearly to the Centaurus Oort clouds.

Anyone wish to correct me on that?

Gary 7