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Old July 7th, 2014, 02:30 PM
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Default Mapping the Local Arm

The "Local Arm" is the galactic arm, in the middle of which Charted Space sits.

I've traced sectors along the Great Rift rimward to the "Great Abyss" region (or whatever you want to call it) halfway to the edge of the arm, but haven't gone further.

Today, though, I started thinking about the rimward border of the local arm. What does it look like? A flat demarcation between "regular density" and "extra rift density"? Or a gradual but regular decrease in density, over the space of a few sectors, until we're in the rift?

I think I like to keep my options open: it can be like it is in the Great Rift with sudden "dropoffs", but could also be gradual, depending on what you want.

I also think that that edge is not a straight line running through the sectors. I tend to prefer that it is rather irregular, with sector-sized dips and promontories, making for varied and interesting "terrain".

Thoughts?
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Old July 7th, 2014, 03:48 PM
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Have you looked at the Zhodani Core Route? (Although Chris Lineham's site is gone the data is included on Travellermap.com.) That cuts across multiple arms and the spaces in between ... albeit without much width.

My gut feeling (based on no evidence at all) is that across a wide boundary, some areas will have sudden drop offs whereas others will have a more gradual petering out. And some areas where there is a sudden drop off may have higher than normal density right up to the 'cliff'.
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Old July 7th, 2014, 03:54 PM
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Quote:
Originally Posted by robject View Post
The "Local Arm" is the galactic arm, in the middle of which Charted Space sits.

I've traced sectors along the Great Rift rimward to the "Great Abyss" region (or whatever you want to call it) halfway to the edge of the arm, but haven't gone further.

Today, though, I started thinking about the rimward border of the local arm. What does it look like? A flat demarcation between "regular density" and "extra rift density"? Or a gradual but regular decrease in density, over the space of a few sectors, until we're in the rift?

I think I like to keep my options open: it can be like it is in the Great Rift with sudden "dropoffs", but could also be gradual, depending on what you want.

I also think that that edge is not a straight line running through the sectors. I tend to prefer that it is rather irregular, with sector-sized dips and promontories, making for varied and interesting "terrain".

Thoughts?

Keep in mind that while the space between the galactic arms is of lower stellar density than within the arms proper, the "arms" are more an "observational" phenomenon than a purely structural one. The spiral structure is believed to be the result of a "density wave" within the galactic disc. Since the areas of higher gas-density are also naturally regions of higher star-formation rates, they appear "brighter" and "bluer" than the rest of the disk, where the remaining (older) stars tend to be dimmer and redder.

So between the spiral arms, while the region does have a lower stellar density than the arms proper, the stars have a much higher degree of probability of being dim red stars (and presumably white dwarfs), whereas within the higher-density arms where star formation is being driven by gas-compression, there are many more younger, brighter and "bluer" stars (which is why the regions stand out as visible "arms").

Theory:
"http://en.wikipedia.org/wiki/Density_wave_theory "
"http://en.wikipedia.org/wiki/Spiral_galaxy#Origin_of_the_spiral_structure "

Nice animation:
https://www.youtube.com/watch?v=c5Us-jonCLA
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Old July 7th, 2014, 04:31 PM
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@Peter: yes, Cliff's data is instructive. He uses a fast drop-off from standard density to sparse.

And @Whorl's note is an interesting and tidy explanation of what arms *are* and why the spaces between look dimmer.

It's almost more intense having a sea of sparse, dead or uninhabitable systems, than to have a lack of stars altogether.
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Old July 8th, 2014, 02:48 PM
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Originally Posted by robject View Post
It's almost more intense having a sea of sparse, dead or uninhabitable systems, than to have a lack of stars altogether.
As an aside, another interesting thought (particularly for a campaign involving one or more "ancients" connections (either capital A- or lowercase a-)) that often get overlooked are the island-like Globular Clusters in the Galactic Halo (above/below the galactic plane). You certainly cannot get to them using standard Jump Drive (but perhaps using a Skip- or Leap-Drive you could), but one wonders what might be (or might have been long, long ago) lurking there in those clusters, staring down from above the galactic plane from a high vantage point, observing, planning, . . .


Globular Clusters
http://en.wikipedia.org/wiki/Globular_cluster
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Old July 8th, 2014, 03:30 PM
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And for my purposes, just identifying the sector of space I've worked is an interesting problem. How do I define its position? As an offset from Core Sector?

I think travellermap.com has an Imperiocentric coordinate system, doesn't it?
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Old July 8th, 2014, 03:50 PM
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Quote:
Originally Posted by robject View Post
And for my purposes, just identifying the sector of space I've worked is an interesting problem. How do I define its position? As an offset from Core Sector?

I think travellermap.com has an Imperiocentric coordinate system, doesn't it?
Yes. The coordinate system is based upon the planet Reference/Core0140 as the Origin. Core Sector is Sector [0,0], Fornast is [0,1], Dagudashaag is [-1,0], Massilia is [0,-1], Lishun is [0,1], Vland is [-1,1], etc.

Simply decide the number of sectors "x" Spinward/Trailing of Core, and the number of sectors "y" Coreward/Rimward of Core, and call it Sector [x,y].


Note that Sol is about 190 Sectors from the Galactic Core. The Perseus Arm is about 50 Sectors Rimward from the Orion Spur (where Charted Space lies).
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Old July 8th, 2014, 08:32 PM
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staring down from above the galactic plane from a high vantage point, observing, planning, . . .
....regarded this earth known space with envious eyes; and slowly, and surely, they drew their plans against us.
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Old July 9th, 2014, 09:19 AM
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Quote:
Originally Posted by whulorigan View Post
As an aside, another interesting thought (particularly for a campaign involving one or more "ancients" connections (either capital A- or lowercase a-)) that often get overlooked are the island-like Globular Clusters in the Galactic Halo (above/below the galactic plane). You certainly cannot get to them using standard Jump Drive (but perhaps using a Skip- or Leap-Drive you could), but one wonders what might be (or might have been long, long ago) lurking there in those clusters, staring down from above the galactic plane from a high vantage point, observing, planning, . . .


Globular Clusters
http://en.wikipedia.org/wiki/Globular_cluster
It is possible, Jump 1 or Jump 2 had been invented there long before it was invented in the galaxy... then they realized the galaxy was too far away for Jump drive to get them there. What affect that would have on their society could make for some interesting adventure hooks.
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Old August 11th, 2014, 07:03 AM
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Quote:
Originally Posted by whulorigan View Post
So between the spiral arms, while the region does have a lower stellar density than the arms proper, the stars have a much higher degree of probability of being dim red stars (and presumably white dwarfs), whereas within the higher-density arms where star formation is being driven by gas-compression, there are many more younger, brighter and "bluer" stars (which is why the regions stand out as visible "arms").
Would the likelihood of the formation of gas giants in these be similar to in the denser arms? If so, then in the "dead" space between the arms it may be possible for "deep space" vessels to refuel on their way between the arms...
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