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In My Traveller Universe Detail what parts of Traveller you do (or don't) use in your campaign.

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Old September 19th, 2020, 03:51 PM
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Default Time and Space in Traveller -- Units

One of the inconsistencies I've noticed in Traveller is the units of the world. In game explanations, that is. Why, for example, should Jumps so neatly correspond to Earth-weeks and parsecs? Even one being exact would be a strange coincidence, but both?

My answer is that they aren't, not quite. That is, they are close enough for many purposes, but not totally. We get similar coincidences--the apparent diameters of the Moon and Sun as seen from Earth are within a few percent, and 2^10 is very close to 10^3, so log (2) = 0.30103 . . . (There are plenty of others, naturally.)

Similarly, is it likely that a Jump (J-1) takes on average exactly 7 days = 168 hours and covers a maximum of 1 parsec? It seems more likely that these were "close enough"--and led to a re-definition of the terms, so that now one week is the average length of time of a jump, and one parsec is the maximum length that can be covered in one jump-1. So, IMTU, I redefined these, and jump one is at most 3.15 light years, taking (on average) 166 hours. (This has the advantage of giving a few extra hours for that trip between the jump-spot and the spaceport.) It removes a bit of the difficulty in believing coincidences, and blurs a bit the Earth-centered cosmos.
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Old September 19th, 2020, 09:09 PM
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There are other unit differences in Traveller (hidden in CT/MT formulae), as well...
C=300 000 000 m/s, not 299 792 458 m/s
G=10 m/s not 9.80665 m/s (explicitly given as 10 on page 54 of The Traveller Book)

These were game simplifications.. and different levels of precision loss...
G is off by 1.971621297792%...
C is off by 0.069228559445%
Imperial Year explicitly defined as 365 days, no leaps. Day explicitly 24 hours, and hours 60 minutes of 60 seconds each. 31,536,000 seconds, vs Earth's 31,557,600.

If we assume C is correct, our G would be 9.813439 or so. And the hex size for a parsec might be altered, too... and the year is defined as 365 days.

I've always assumed that the year is that of Sylea/Capitol, not of Earth. And, since I noted the discrepancy, G and C, as well, being in Sylean units, not Earth units.
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Old September 19th, 2020, 10:16 PM
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I had heard that one week in Jump Space was an out-of-game throwback to Play-by-Mail gaming where people only replied (?) or heard from the GM once a week.
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Old September 20th, 2020, 07:12 AM
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It's now part of the DNA of the game.

I had a go at creating a algorithm for jump time, experienced and universe, that doesn't necessarily default at exactly one hundred sixty eight hours, just about that period, combined with exit point, but since we don't have precise star charts in real life, sort of pointless.

You could rule that jump drives don't cycle at the same rate, so the time varies slightly for each starship jump.
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Old September 20th, 2020, 06:48 PM
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Quote:
Originally Posted by aramis View Post
There are other unit differences in Traveller (hidden in CT/MT formulae), as well...
C=300 000 000 m/s, not 299 792 458 m/s
G=10 m/s not 9.80665 m/s (explicitly given as 10 on page 54 of The Traveller Book)

. . .

I've always assumed that the year is that of Sylea/Capitol, not of Earth. And, since I noted the discrepancy, G and C, as well, being in Sylean units, not Earth units.
I'd noticed or learned of some of these, but they failed to come to mind when I posted.

Still, the Sylea/Capital explanation would be yet another coincidence. I'd still prefer close--like within 5%, or even 1%, but not necessarily exact--only close enough for uplifted game porpoises.
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Old September 21st, 2020, 04:08 AM
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Quote:
Originally Posted by Spinward Scout View Post
I had heard that one week in Jump Space was an out-of-game throwback to Play-by-Mail gaming where people only replied (?) or heard from the GM once a week.
Sounds plausible. And the picaresque SciFi it was based on favored "world of the week" campaigns, with (one hoped) weekly sessions.
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Old September 21st, 2020, 11:38 AM
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Quote:
Originally Posted by BRover View Post
Why, for example, should Jumps so neatly correspond to Earth-weeks and parsecs? Even one being exact would be a strange coincidence, but both?
Because it's a game of adventure and exploration, not quantum physics.

Get on the ship from T-Shirt world A, fly in a week, dodging pirates, to T-Shirt world B, explore the world, avoid being eaten by a grue, bargain a cargo manifest, steal a secret document, get drunk in a bar with your buddies, brawl with some locals, and skip out to the next star system minutes ahead of the local lawmen. Hooting and hollering the live long day.
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Old September 21st, 2020, 04:17 PM
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Quote:
Originally Posted by BRover View Post
Why, for example, should Jumps so neatly correspond to Earth-weeks and parsecs?
You should REALLY ask, "Why do Earth-weeks and parsecs so neatly correspond to Jump space physics?"

THAT really bothers me.
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Old September 21st, 2020, 05:28 PM
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Calculating the value of a parsec
By the 2015 definition, 1 au of arc length subtends an angle of 1″ at the center of the circle of radius 1 pc. Converting from degree/minute/second units to radians,

{\displaystyle {\frac {1{\mbox{ pc}}}{1{\mbox{ au}}}}={\frac {180\times 60\times 60}{\pi }}}{\displaystyle {\frac {1{\mbox{ pc}}}{1{\mbox{ au}}}}={\frac {180\times 60\times 60}{\pi }}}, and
{\displaystyle 1{\mbox{ au}}=149\,597\,870\,700{\mbox{ m}}}{\displaystyle 1{\mbox{ au}}=149\,597\,870\,700{\mbox{ m}}} (exact by the 2012 definition of the au)
Therefore,

{\displaystyle \pi {\mbox{ pc}}=180\times 60\times 60{\mbox{ au}}=180\times 60\times 60\times 149\,597\,870\,700=96\,939\,420\,213\,600\,000{\mb ox{ m}}}{\displaystyle \pi {\mbox{ pc}}=180\times 60\times 60{\mbox{ au}}=180\times 60\times 60\times 149\,597\,870\,700=96\,939\,420\,213\,600\,000{\mb ox{ m}}} (exact by the 2015 definition)
Therefore,

{\displaystyle 1{\mbox{ pc}}={\frac {96\,939\,420\,213\,600\,000}{\pi }}=30\,856\,775\,814\,913\,673{\mbox{ m}}}{\displaystyle 1{\mbox{ pc}}={\frac {96\,939\,420\,213\,600\,000}{\pi }}=30\,856\,775\,814\,913\,673{\mbox{ m}}} (to the nearest metre)
Approximately,


In the diagram above (not to scale), S represents the Sun, and E the Earth at one point in its orbit. Thus the distance ES is one astronomical unit (au). The angle SDE is one arcsecond (
1
/
3600
of a degree) so by definition D is a point in space at a distance of one parsec from the Sun. Through trigonometry, the distance SD is calculated as follows:

{\displaystyle \mathrm {SD} ={\frac {\mathrm {ES} }{\tan 1''}}}{\displaystyle \mathrm {SD} ={\frac {\mathrm {ES} }{\tan 1''}}}
{\displaystyle \mathrm {SD} \approx {\frac {\mathrm {ES} }{1''}}={\frac {1\,{\mbox{au}}}{{\frac {1}{60\times 60}}\times {\frac {\pi }{180}}}}={\frac {648\,000}{\pi }}\,{\mbox{au}}\approx 206\,264.81{\mbox{ au}}.}{\displaystyle \mathrm {SD} \approx {\frac {\mathrm {ES} }{1''}}={\frac {1\,{\mbox{au}}}{{\frac {1}{60\times 60}}\times {\frac {\pi }{180}}}}={\frac {648\,000}{\pi }}\,{\mbox{au}}\approx 206\,264.81{\mbox{ au}}.}
Because the astronomical unit is defined to be 149597870700 m,[9] the following can be calculated:

Therefore, 1 parsec ≈ 206264.806247096 astronomical units
≈ 3.0856775811016 metres
≈ 30.856775815 trillion kilometres
≈ 19.173511577 trillion miles
Therefore, if 1 ly ≈ 9.461015 m,

Then 1 pc ≈ 3.261563777 ly

https://en.wikipedia.org/wiki/Parsec



Rather dependent on what one supposes is the Third Rock from the Sun's unique orbit.

So the Universe really does revolve around the Earth.
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Old September 22nd, 2020, 01:37 PM
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Quote:
Originally Posted by whartung View Post
Because it's a game of adventure and exploration, not quantum physics.

Get on the ship from T-Shirt world A, fly in a week, dodging pirates, to T-Shirt world B, explore the world, avoid being eaten by a grue, bargain a cargo manifest, steal a secret document, get drunk in a bar with your buddies, brawl with some locals, and skip out to the next star system minutes ahead of the local lawmen. Hooting and hollering the live long day.
That's the game explanation, but not the in-universe explanation. I can accept it, but the exact equivalence is harder to explain.
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