Stellar Information

[ovka]

I am looking at putting together a Traveller campaign for the first time in years. I have some questions regarding the stellar information on the Traveller map. I am sure this has been discussed many times before, but my Search Fu is somewhat lacking.

1. How does one look at a list of stars in a system and determine where those stars are placed. Obviously, the first star is the primary star, but, for example, I see that Castor (Solo 2339) has "A1 V M5 V A2 V M2 V M1 V M1 V" for its stars. Based on the Wiki, it appears that the M5 V orbits the A1 V (probably as a companion star), and that the A2 V orbits the A1 V at a close (or perhaps near) radius with the M2 V orbiting the A2 V (again, probably as a companion star). Finally, the M1 V/M1 V pair form a distant pair that orbits the first four stars. Is that the only way to read this? Is it possible to determine this based on the listing? Another example is Lima (Dark 2511) which has "M0 V M8 V M6 V M3 V." How would this be parsed?

2. Does the presence of multiple stars change the radius of the jump shadow at all? For example, in the instance of Castor, would the radius be determined from the center of the primary star, the center of gravity of the four stars (which could very well be the center of the primary star), or does the presence of the A2 V/M2 V pair orbiting the A1 extend this?

3. What is the formula for determining the radius of a star (for the purpose of determining the jump shadow) Muravia (Thet 1628) orbits an A7 Ia star, what would its radius be?

4. What is the formula for determining the habitable zone of a star (again looking at Castor, Lima, and Mauravia)?

Thank you in advance for indulging me.

Cheers,

Baron Ovka

 

[Spinward Flow]

You want CT LBB6 Scouts: Extended System Generation for the answers to your questions.

 

[whulorigan]

1. How does one look at a list of stars in a system and determine where those stars are placed. Obviously, the first star is the primary star, but, for example, I see that Castor (Solo 2339) has "A1 V M5 V A2 V M2 V M1 V M1 V" for its stars. Based on the Wiki, it appears that the M5 V orbits the A1 V (probably as a companion star), and that the A2 V orbits the A1 V at a close (or perhaps near) radius with the M2 V orbiting the A2 V (again, probably as a companion star). Finally, the M1 V/M1 V pair form a distant pair that orbits the first four stars. Is that the only way to read this? Is it possible to determine this based on the listing? Another example is Lima (Dark 2511) which has "M0 V M8 V M6 V M3 V." How would this be parsed?

An attempt was made early on to try and parse this info, but unfortunately the proposed notation ran into some issues potentially involving copyright. So there is currently no specific way to make a definitive determination except to note the following:

1. The FIRST star listed is normally the star about which the mainworld orbits - this is usually (BUT NOT ALWAYS) the most massive star in the system.
2. Certain stars are real-universe stars and can be detailed based on actual astronomy. I have most of the real-world stars with OTU worlds detailed on the wiki, linked to their OTU worlds (i.e. the star has a separate page on the wiki that has links on the OTU world page).

2. Does the presence of multiple stars change the radius of the jump shadow at all? For example, in the instance of Castor, would the radius be determined from the center of the primary star, the center of gravity of the four stars (which could very well be the center of the primary star), or does the presence of the A2 V/M2 V pair orbiting the A1 extend this?

Each individual star has its own individual 100-dia jump shadow. So in the case of Castor there would be 6 separate jump-shadows one for each star which may or may not overlap depending on the stellar configuration and separation of the stars.

 

[whulorigan]

The jump shadow would be determined by the barycenter of all the stars; though with hexanary, or other stellar arity, it's best to look at some source as the orbits, such as A-C, could be a close, and B a far companion.

Not according to T5. It is strictly a sphere centered on the centers of mass of individual objects.

 

[ovka]

You want CT LBB6 Scouts: Extended System Generation for the answers to your questions.

35-40 years ago, that is exactly what I would have done (did do), interpolating to get values between lines. I was hoping that in an era where a computer can perform more precise (if not more correct ) calculations, I could throw a formula into a spreadsheet and let it do the work.

Cheers,

Baron Ovka

 

[ovka]

An attempt was made early on to try and parse this info, but unfortunately the proposed notation ran into some issues potentially involving copyright. So there is currently no specific way to make a definitive determination except to note the following:

1. The FIRST star listed is normally the star about which the mainworld orbits - this is usually (BUT NOT ALWAYS) the most massive star in the system.
2. Certain stars are real-universe stars and can be detailed based on actual astronomy. I have most of the real-world stars with OTU worlds detailed on the wiki, linked to their OTU worlds (i.e. the star has a separate page on the wiki that has links on the OTU world page).

Thanks! That's good to know. I'll have a look.

Each individual star has its own individual 100-dia jump shadow. So in the case of Castor there would be 6 separate jump-shadows one for each star which may or may not overlap depending on the stellar configuration and separation of the stars.

I *thought* that might be the case, but wasn't quite sure.

Cheers,

Baron Ovka

 

[Garnfellow]

An attempt was made early on to try and parse this info, but unfortunately the proposed notation ran into some issues potentially involving copyright.

I didn't realize there was a copyright problem -- I thought Don McKinney considered stellar notation too big a project to add to the T5SS.

 

[Garnfellow]

Not according to T5. It is strictly a sphere centered on the centers of mass of individual objects.

And I don't think I've caught that before. Can you point me to where I should look?

 

[Spinward Flow]

It is strictly a sphere centered on the centers of mass of individual objects.

This is consistent with CT (just pointing out for reference).

Sol in the Terra system is 695,700km in radius ... which is 1,391,400km diameter.
139,140,000km is 0.93 AU (Terra's orbit is 149,600,000km or 1 AU) is 100 diameters away from Sol.

Terra's equitorial radius is 6378.137km ... which is 12,756.274km diameter.
1,275,627.4km is 100 diameters away from Terra ... not enough to impinge on Sol's 0.93 AU jump shadow from Terra's orbit around Sol.

Luna's equitorial radius is 1738.1km ... which is 3476.2km diameter.
347,620km is less than Luna's perigee distance (362,600km) and not still completely within Terra's own jump shadow from Luna's apogee distance (405,400km) meaning that where Luna is in orbit has no effect on the 100 diameters limit of Terra's own gravity well (Luna's jump shadow is always within Terra's jump shadow). However, Luna's orbital position could potentially be relevant for being within 10 diameters for misjump calculations if using Luna for a gravity whip assist to exit Terra's 100 diameter jump shadow.

Just pointing that out for reference to help with the task of how to think about such matters.
Point being that each mass casts its own jump shadow.
Some jump shadows can be "contained within" other jump shadows, depending on orbits and positioning.

 

[whulorigan]

And I don't think I've caught that before. Can you point me to where I should look?

It is in the "How Jump Works" Chapter of of T5.10 Book 2.

 

[whulorigan]

I didn't realize there was a copyright problem -- I thought Don McKinney considered stellar notation too big a project to add to the T5SS.

I think it ended up being a little bit of both. I do not believe there was an explicit copyright issue that would have been violated, but rather the person in question who had invented the notation was being cantankerous enough to potentially cause problems down the line if implemented.

 

[robject]

I think it ended up being a little bit of both. I do not believe there was an explicit copyright issue that would have been violated, but rather the person in question who had invented the notation was being cantankerous enough to potentially cause problems down the line if implemented.

Ah yes, I remember that. Well it doesn't matter -- there are many notational styles that would help, even if some are less all-encompassing than others.

I think that the most common trope should be the least annotated, if you get my drift.

Like in Spanish, the accent is on the penultimate syllable. Since most words follow the rule, you don't have to annotate that. When it isn't, then you add an accent.

So set down a most-common grammar and then introduce "accents" for the exceptions.

 

[whulorigan]

Ah yes, I remember that. Well it doesn't matter -- there are many notational styles that would help, even if some are less all-encompassing than others.

I had thought that a simple jot of some kind would be helpful to split near stars from companions and secondary system stars. For example:

A1 V M5 V A2 V M2 V M1 V M1 V

If you use "a comma after companions" and "plus stars for distance", then you could have:

A1 V M5 V, +A2 V, M2 V M1 V M1 V

Thus "A1 V M5 V" would be a primary and its close companion.
Then "+A2 V" marks a far system star -- 1D x 1000 AU away in Book 6 terms.
And "A2 V," means it has no close companions -- the remaining stars are "Near" to it, in their own orbits.

That could work.

IIRC, the system that was being considered was using [brackets], (parentheses), and {braces} for [Close], Near, (Far) and {Extreme} Companions, with an asterisk (*) on the primary (or primary group) of the main world. (A Near Companion had no punctuation notations).

So your example above could have been:

[A1 V M5 V]*, M2 V, M1 V, M1 V, (A2 V)

If the two M1 V stars were themselves a close orbiting pair, then:
[A1 V M5 V]*, M2 V, [M1 V M1 V], (A2 V)

If the M1 V pair were orbiting the Far Companion:
[A1 V M5 V]*, M2 V, (A2 V [M1 V M1 V])

 

[robject]

My house rules follow. You have been warned.

Castor (Solo 2339) has "A1 V M5 V A2 V M2 V M1 V M1 V" for its stars. Based on the Wiki, it appears that the M5 V orbits the A1 V (probably as a companion star), and that the A2 V orbits the A1 V at a close (or perhaps near) radius with the M2 V orbiting the A2 V (again, probably as a companion star). Finally, the M1 V/M1 V pair form a distant pair that orbits the first four stars. Is that the only way to read this? Is it possible to determine this based on the listing? Another example is Lima (Dark 2511) which has "M0 V M8 V M6 V M3 V." How would this be parsed?

The first star is the mainworld star. That's established.
Break the stars up into Systems. If there are more than four stars, split the remainder off and resolve as a Far System.
Now for each System:
1. If the second star is significantly smaller, then I call it a binary companion. Move to the next star.
2. The current star is Close.
3. The next star is Near. Any star left over becomes its binary companion.

Example: A1 V M5 V A2 V M2 V M1 V M1 V

A1 V = mainworld star
Mainworld system = A1 V M5 V A2 V M2 V
Far system = M1 V M1 V

Mainworld: the M5 V is Close, the A2 V is Near, and the M2 V is its binary companion.
Far system: The second M1 V is Close.


(Traveller5 assigns the same 16% probability for the presence of Close Stars, Near Stars, and Far Stars, and has a further 16% chance that each of those stars will have a Companion. T5 implicitly sets a hard limit of 8 stars per system -- which is insanely high, but thankfully highly unlikely.)

 

[robject]

IIRC, the system that was being considered was using [brackets], (parentheses), and {braces} for [Close], Near, (Far) and {Extreme} Companions, with an asterisk (*) on the primary (or primary group) of the main world. (A Near Companion had no punctuation notations).

So your example above could have been:

[A1 V M5 V]*, M2 V, M1 V, M1 V, (A2 V)

If the two M1 V stars were themselves a close orbiting pair, then:
[A1 V M5 V]*, M2 V, [M1 V M1 V], (A2 V)

If the M1 V pair were orbiting the Far Companion:
[A1 V M5 V]*, M2 V, (A2 V [M1 V M1 V])

I remember that.

I preferred always putting the mainworld system first, thus we remove the asterisk... but then I was also fairly sloppy about things, not wanting pure accuracy but rather a good-enough guide.


The problem with my comma is that too many star systems would require it. Binary companions aren't as common as Close/Near/Far stars, so that's cumbersome.

 

[robject]

Maybe instead, I could use a mark that "binds" a star as a binary companion.

A1 V M5 V A2 V M2 V M1 V M1 V

I would grab the smallest star -- is it the M5 V? -- and subordinate it as a binary companion, probably to the A1 V since that appears to be the intent.

THEN, I would read this as Mainworld Star A1 V with binary M5 V, Close Star A2 V, and Near Star M2 V. Then I'd read a Far System with a Main star as the M1 V and either a Close or Near star for the M1 V.


****

If I say "plus a companion" then maybe

A1 V +M5 V A2 V +M2 V M1 V M1 V

That means the two A-class stars each have a close companion.

Now I need something to split the Far system from the Mainworld system. A slash or splat or colon or something.

A1 V +M5 V  A5 V +M2 V M1 V M1 V
A2 V +M5 V // A9 V +M2 V M1 V M1 V
A3 V +M5 V  A9 V // M2 V M1 V M1 V
A4 V +M5 V  A9 V  M2 V M1 V // M1 V
A5 V  M5 V  A9 V  M2 V M1 V M1 V

Thus example "A1" has two binary companions in one star system.
"A2" has a Far system beginning with the A9 V, which still has a binary companion.
"A3" has the Far system beginning with the M2 V.
"A4" has the Far system with the last star only, and the only binary companion is the M5 V.

"A5" suggests there is only one star system with no binary companions and five Close and Near stars.

Go by your rule system for further clarification.

 

[robject]

My rules of thumb.

1. The first star is the mainworld star.
2. If the second star looks significantly tiny compared to the mainworld star, then make it a binary companion.
3. The next two stars are, in order: Close and Near. This is a useful simplification.

That takes care of three to four stars.

4. Alternate assigning remaining stars between the Far system and binary companions, however you like. In order. Random. ?

Example
A1 V M5 V A2 V M2 V M1 V M1 V

A1 V = mainworld star.
M5 V = Close. I'll claim that it's not supremely diminutive and therefore has its own orbit.
A2 V = Near.
M2 V = Far (main star).
M1 V = would be a binary companion -- anywhere you like. I do "in order", so it's binary to the A1 V.
M1 V = would then be in the Far system, either Close or Near.

 

[whulorigan]

Now I need something to split the Far system from the Mainworld system. A slash or splat or colon or something.

I would probably go with slash ("/" or "\") , but that is just my personal preference, as a slash already is a "divider" by nature.
You could also use " | " or " || ".

 

[robject]

Regina's stars:

F7 V BD M3 V

1. F7 V is the mainworld star.
2. BD is tiny, so it's the binary companion.
3. M3 V (Derida) is actually the Far star, but without knowing that, I'd read it as Close, which would be "wrong".

So I'd be tempted to write it as

F7 V BD // M3 V

 

[whulorigan]

Or: F7 V BD || M3 V

Perhaps :
| = Near
and
|| = Far