Determining the Qualities of Stars

[AlexanderHowl]

Why not just use G-type main sequence stars? It is easier if you can connect Sol.

[Varyon]

Originally Posted by Humabout

I dont have the equation for absolute magnitutde from luminosity on hand, but Jon Zeigler (author of GURPS Space) has been publishing an update to the star and planet generation system that incorporates modern planetology here.

Neat. I'll keep an eye on it if I need deeper details, but so far I'm happy with what I'm getting out of Space. Well, mostly - I'd really like a way to determine the heliopause (but after trying to look it up, I get the feeling we don't actually have any idea of where the heliopause is for any star other than Sol), and determination of planet subtype with a basis on more than just its orbit would be nice (the mentioned possibility of high albedo meaning an ice planet or high greenhouse meaning a greenhouse planet in the habitable zone), although I think I have a kludge for that, which is roughly actually rolling to determine the ratio of the habitable zone planet, and use the resulting temperature instead of the true blackbody temperature. The further it is from 1.11 AU, the higher its albedo (and beyond 1.14 AU, an otherwise-Ocean/Garden world is Ice, and quite bright), while the closer it is, the more of a greenhouse effect is has (and less than 1 AU, an otherwise-Ocean/Garden world has a runaway greenhouse effect and is a Greenhouse planet.

Originally Posted by AlexanderHowl

Why not just use G-type main sequence stars? It is easier if you can connect Sol.

Sol being cut off is a feature, not a bug. I also feel it's necessary for making FTL travel easy, yet never discovered on Earth - it's literally impossible within our solar system, and indeed in many solar systems. "Aetheric stars" aren't actually the only ones where boost drives and entering/exiting hyperspace is possible, however, but they are much easier than the others, and how you enter hyperspace sort of "attunes" your ship to make it easier to detect and utilize very similar systems, hence humans having only colonized the aetherics. The setting's "aliens" do make use of some of the other eligible star systems but essentially nobody actually knows that (nor do they know the "aliens" are actually engineered lifeforms based on Earth life).

For the purposes of the setting, only the aetheric systems really matter. Earth is a distant theocracy on a 5-year communication delay, while the Malakim are a threat that can somehow enter - and apparently exit - hyperspace without being at an aetheric heliopause, although not reliably. Nobody can visit Earth (and while Earth occasionally sends new colonists - primarily to further along the Caliphate's spread into Harpyia so it can seize power and force humanity to return to Earth - said colonists are still a few generations removed from anyone who's actually seen Earth), and hitching a ride on one of the Malakim's biological ships to see where they are based is impossible (it will detect you, and if you kill all of its crew and prevent it from making more, it's more likely to just stay in hyperspace long enough for the aether to kill it than try to return home).

[Fred Brackin]

Originally Posted by Varyon

Neat. I'll keep an eye on it if I need deeper details, but so far I'm happy with what I'm getting out of Space. Well, mostly - I'd really like a way to determine the heliopause (but after trying to look it up, I get the feeling we don't actually have any idea of where the heliopause is for any star other than Sol), e).

<shrug> The distance to the heliopause should be similar for stars with solar wind activity similar to Sol in areas of space similar to the "Local Bubble" where interstellar space is thin but energetic.

A G0 probably has at least a little more acivity than a G2 though I know of no one who has collected data on this. It' hard for me to say evven in theory what having your star in a colder but thicker interstellar medium might do. My intuition gives a 60/40 chances that it might push the heliopause farther out.

Combine that witht he bigger star and the heliopause might be a long way out though you have to go about 100 ly before you're out of the bubble.

I'm not even sure what the "official" distance for our heliopause is. There ahve been announcemnts that the Voyager probes have crossed the heliopause 3 or 4 times in my lifetime.

It's definitely a long way out. If it was 80 AU that'd be about a month at 1G and turnover velocity would be enormous. WMD issues are a definite thing and a drive that can do it makes STL interstellar flight pretty reasonable.

[Varyon]

Originally Posted by Fred Brackin

It's definitely a long way out. If it was 80 AU that'd be about a month at 1G and turnover velocity would be enormous. WMD issues are a definite thing and a drive that can do it makes STL interstellar flight pretty reasonable.

For the original generation ships, I haven't designed them yet, but the current intent is for them to be roughly 50% fuel, and they had a delta-v a bit north of 2% light speed, but rather low acceleration - something like 0.05G IIRC - thanks to their small drives (the amount of time spent accelerating is so small compared to the whole trip, using sub-system engines doesn't make a lot of difference). They accelerated to 1% light speed, then traveled for 500 years to reach Harpyia Mati. Modern ships of a similar design can manage delta-v's of around 5% light speed, and as the drives can function in a pseudovelocity "boost drive" mode once they enter an aetheric star's heliosphere that also sync's them to the system they are in (functioning as a rather efficient braking system), modern ships coming from Earth can make the journey in "only" 100 years.

One thing I intend to use the heliopause distance to determine is actually the speed of the pseudovelocity boost drives - I want a typical freighter to take roughly 1 month to go from 1.11 AU to the heliopause, making interstellar journeys typically take 2 months, plus the time in hyperspace. With my initial estimate of 88 AU for the heliosphere, that's 86.89 AU per month, or right around 3000 mps. That's roughly Earth's solar orbit to Mars' solar orbit in 4 hours, 20 minutes (or Gateway to the next furthest orbit in 6 hours, 20 minutes).

[Agemegos]

Are you using real stellar data for position etc.? If so, are you aware of the Extended Hipparcos compilation of stellar data? I find it pretty useful.

I count 295 G0V stars within 200 light-years.

[Agemegos]

Originally Posted by Varyon

Harpyia is the romanization of the Greek word ἅρπυια - the harpy. I can't remember why I added the n on the end of it (probably to make it possessive or similar)

άρπυια is a first-declension feminine noun ending in -α. I think the genitive is άρπυιασ. "Harpyias".

[Varyon]

Originally Posted by Agemegos

Are you using real stellar data for position etc.? If so, are you aware of the Extended Hipparcos compilation of stellar data? I find it pretty useful.

I count 295 G0V stars within 200 light-years.

I wasn't planning on it - Earth's night sky looks more-or-less the same as in reality, with the glaring exception of the Harpy constellation, but I intended to pretty much just throw the aetheric systems around semi-randomly. Assuming I'm using the catalog properly, I'm pretty certain I'll still need to do that - the catalogue only contains 4 G0V stars between 3 and 5 billion years old, and maybe only 3 of them (HIP 726, 12099, and and 33460) are around the right age to be aetheric (the 4th is 4.7 billion years old, the other three are 4.1, 4.1, and 4.0, respectively). They're also all quite a bit brighter than Harpyian Mati. I haven't yet decided how distant systems will be from each other, although I initially intended to have them be relatively clustered together, with Harpyian Mati some distance from the main cluster. I may still do so.

Originally Posted by Agemegos

άρπυια is a first-declension feminine noun ending in -α. I think the genitive is άρπυιασ. "Harpyias".

I thought that might be the case, actually. I'll probably change it to Harpyias Mati, then.