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Imperial Interstellar Scout Service Details of the worlds of the Imperium (and beyond).

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  #1  
Old January 17th, 2015, 09:31 AM
Garnfellow Garnfellow is offline
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Default Eakhoi (Dark Nebula 2123)

Eakhoi is a high-population Aslan garden world in Khtoiakta subsector (K) of Dark Nebula, 9 parsecs trailing from Kusyu, about 4 parsecs from the Solomani Confederation border, and roughly 61 parsecs spinward of Terra.

What's really notable about this system is that the mainworld orbits a yellow supergiant, spectral type F8 Ia -- the same as Delta Canis Majoris. It's a busy little system, with 4 gas giants, 1 asteroid belt, and 9 other worlds.

It looks like T5 allows a habitable zone for even F8 Ia stars -- way out in orbit 12. But can the rest of the system details be reconciled with this star? I'm fine with implausible, I'm just curious where the impossible line lies.

Shouldn't a star like this be visible to the naked eye from Earth? It seems like it would be one of the most remarkable astrographic features in this part of Charted Space.
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Old January 17th, 2015, 02:41 PM
tjoneslo tjoneslo is offline
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There was, many years ago, a long discussion on the JTAS boards about Antares, which is another supergiant star with several billion people on a habitable world.

From what I remember about that discussion here were the problems raised:

1) the 100D limit for the star is somewhere about 2-4 week out from orbit 12 even assuming a 1G or 2G drive on the ships. This makes trade with the system hugely difficult. There is probably a trade station somewhere in the outer system (say orbit 18) (or several).

2) There isn't enough time for world to (depending upon the which research papers you have read) have formed, cooled to the point where they have a solid surface, or have any kind of atmosphere. The solution to this problem for Antares was to add a third (brown dwarf) companion star where the world was orbited. This put it outside the 100D limit for the primary, and gives enough time to have the world form a real garden worlds (with life and everything). I could also see using a captured deep space wandering planet, now warmed and aggressively terraformed.

3) The star will go supernova. Probably not in the timescale of anyone currently living in the system, but on a stellar lifespan scale, real soon now. There will be essentially no warning, and what little warning there will be (if people are paying attention) there is no way to get everyone off the planet.

Yes, you should be able to see the star with a naked eye from Terra during daylight hours. The same effect should be true in the Spinward Marches and Deneb sectors with regard to the Deneb system. And the Antares sector and Antares star.
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Old January 17th, 2015, 03:41 PM
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Quote:
Originally Posted by Garnfellow View Post
Eakhoi is a high-population Aslan garden world in Khtoiakta subsector (K) of Dark Nebula, 9 parsecs trailing from Kusyu, about 4 parsecs from the Solomani Confederation border, and roughly 61 parsecs spinward of Terra.

What's really notable about this system is that the mainworld orbits a yellow supergiant, spectral type F8 Ia -- the same as Delta Canis Majoris. It's a busy little system, with 4 gas giants, 1 asteroid belt, and 9 other worlds.

It looks like T5 allows a habitable zone for even F8 Ia stars -- way out in orbit 12. But can the rest of the system details be reconciled with this star? I'm fine with implausible, I'm just curious where the impossible line lies.

Shouldn't a star like this be visible to the naked eye from Earth? It seems like it would be one of the most remarkable astrographic features in this part of Charted Space.
Note that down in the left corner of TravellerMap, Dark Nebula Sector is noted as being "Unreviewed", meaninig that some of the data of Dark Nebula is likely to change when it gets the full T5 treatment (it will say "Traveller 5 Second Survey" instead of "Unreviewed" when this is done).

But to your point: Delta Canis Majoris lies a little under 500pc from Earth in a generally Rimward direction, and as you mentioned, Eakhoi's Star lies at a distance of a little under 70pc to Spinward. So yes, an F8Ia star in Dark Nebula Sector would be quite bright in Terra's sky if it were at that distance, unless it were obscured by intervening dust clouds (remember, this Sector is called the "Dark Nebula").

NOTE:
I was able to locate the following stars along a Spinward/RimSpinward bearing that could possibly fit with a little tweaking (keeping in mind that the distances on TravellerMap are projections/compressions of 3D space onto a 2D plane, and that the hexes really have to do with the distance thru Jumpspace, and generally approximate 1pc distances as transformed from NormalSpace):
1) HD 199290: Type F2Ib / Distance ~160pc
2) HD 203918: Type F8 (Luminosity unspecified) / Distance ~ 90pc
3) HD 15000: Type F5II / Distance ~ 80pc
4) EM* CDS 283: Type F6Iab / Distance unspecified *
5) V* VY Persei: Type F7.5Ib / Distance unspecified *
6) IRAS 02143+5852: Type F7I / Distance unspecified *

* - Note that this probably means that an accurate parallax measuremneant cannot be obtained (i.e. it might be very far away).
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Old January 17th, 2015, 04:00 PM
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Quote:
Originally Posted by whulorigan View Post
[...] (keeping in mind that the distances on TravellerMap are projections/compressions of 3D space onto a 2D plane, and that the hexes really have to do with the distance thru Jumpspace, and generally approximate 1pc distances as transformed from NormalSpace):
Unfortunately, Traveller maps show accurate realspace distances that can be traversed with SLT and are transitive (if that's the term I want). So that handwave makes no more sense than the flat galaxy does.


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Old January 17th, 2015, 04:36 PM
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Quote:
Originally Posted by tjoneslo View Post
1) the 100D limit for the star is somewhere about 2-4 week out from orbit 12 even assuming a 1G or 2G drive on the ships. This makes trade with the system hugely difficult. There is probably a trade station somewhere in the outer system (say orbit 18) (or several).
I was a little surprised to find that when I checked the T5 book, the 100-diameter limit for a both a F5 Ia and a G0 Ia was within orbit 11. I was expecting it to be well outside the habitable zone.

Is this right? Or am I maybe misreading the chart?
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Old January 17th, 2015, 04:55 PM
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Quote:
Originally Posted by whulorigan View Post
Note that down in the left corner of TravellerMap, Dark Nebula Sector is noted as being "Unreviewed", meaninig that some of the data of Dark Nebula is likely to change when it gets the full T5 treatment (it will say "Traveller 5 Second Survey" instead of "Unreviewed" when this is done).
And that's exactly why I'm looking at the data. I guess my ultimate question here is, should we recommend that Marc chuck this supergiant, or can we find a reasonable way to make it work?

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Originally Posted by whulorigan View Post
So yes, an F81a star in Dark Nebula Sector would be quite bright in Terra's sky if it were at that distance, unless it were obscured by intervening dust clouds (remember, this Sector is called the "Dark Nebula").
And that's one of the other questions I have in the back of my mind as I'm reviewing the data: if there really is a dark nebula in this Sector, where would it be and what would it look like? The boardgame -- which of course has only the most tenuous of connection to the canonical UWP data -- features a nebula maybe 2 parsecs in width, with some six stars within it.

Could you have some kind of dust cloud that large 50-80 parsecs from Terra that we haven't yet detected, or is that just too close? Maybe not a true nebula, but something smaller and closer.

I am fine with the sector name being just some sort of poetical or marketing device like "Greenland," but if one could shoehorn a reasonable astronomical explanation, that seems far more preferential.
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Old January 17th, 2015, 05:25 PM
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Quote:
Originally Posted by Garnfellow View Post
And that's one of the other questions I have in the back of my mind as I'm reviewing the data: if there really is a dark nebula in this Sector, where would it be and what would it look like? The boardgame -- which of course has only the most tenuous of connection to the canonical UWP data -- features a nebula maybe 2 parsecs in width, with some six stars within it.

Could you have some kind of dust cloud that large 50-80 parsecs from Terra that we haven't yet detected, or is that just too close? Maybe not a true nebula, but something smaller and closer.

I am fine with the sector name being just some sort of poetical or marketing device like "Greenland," but if one could shoehorn a reasonable astronomical explanation, that seems far more preferential.

There actually is a massive set of dust clouds called the Great Rift (or sometimes the Cygnus Rift) that lies at about the distance (~ 80pc -100pc) of the Great Rift on Traveller Map, although it begins at a bearing somewhat counter-clockwise from Deneb's bearing, and continues over toward the Lesser Rift and 2000 Worlds, as seen from Earth *. Note that this is a rift in terms of visibility, not in terms of low stellar density. Perhaps there could be some outlying pockets of these clouds in the Dark Nebula.
* - Note that this is not a single continuous formation, but are overlapping bands and pockets of nebular formations at varying distances that merely look like a continuous band from Earth. It is called a rift because it is black and you cannot see any stars through it.
http://en.wikipedia.org/wiki/Great_Rift_%28astronomy%29

P.S. And I am all for placing an actual "Dark Nebula" of some sort (perhaps 1-3pc wide) somewhere in the Dark Nebula Sector. ISTR somewhere once seeing a map of Charted Space that located the rough position of the nebula, but I do not remember where (and I do not think it was the Dark Nebula boardgame).
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Old January 17th, 2015, 06:06 PM
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Quote:
Originally Posted by whulorigan View Post
Note that down in the left corner of TravellerMap, Dark Nebula Sector is noted as being "Unreviewed", meaninig that some of the data of Dark Nebula is likely to change when it gets the full T5 treatment (it will say "Traveller 5 Second Survey" instead of "Unreviewed" when this is done).
"Unreviewed" is a bit of a misnomer in this case. It should really say "under review" and this is the sort of feedback Marc, DonM and company want before it gets the stamp of approval (and why the data is up on TM). So... paging DonM!
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Old January 17th, 2015, 07:30 PM
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"Unreviewed" is a bit of a misnomer in this case. It should really say "under review" and this is the sort of feedback Marc, DonM and company want before it gets the stamp of approval (and why the data is up on TM). So... paging DonM!
FYI, to clarify this, I've split out "In Review" from "Unreviewed" on the map site. Sorry for the confusion.
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Old January 18th, 2015, 12:26 AM
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Doing some calculations, an F8 Ia star has an absolute magnitude of -5.9. For comparison the sun is 4.83. For magnitudes, smaller numbers means brighter objects. At the 61 parsecs distance, the star has an apparent magnitude of -2, which makes it brighter than Sirius (the brightest star in the sky, m=1.47), and about the brightness of Jupiter.

That's with visible light. If there is a nebula in the way, it may dim the star some, but there would be other instruments that would see a star that bright.
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