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How Big is a Parsec?

Chuck Anumia

SOC-14 1K
OK
This may not be a long post but I was wondering how a Parsec is measured?
How many Light years across?
How many Kilometers across?
How many AU's?
 
A unit of astronomical length based on the distance from Earth at which stellar parallax is one second of arc and equal to 3.258 light-years, 3.086 × 10^13 kilometers, 1.918 × 10^13 miles, 206265 AU.
 
http://en.wikipedia.org/wiki/Parsec

Interestingly, the definition is tied to the Earth's orbit (being based on 1 AU, which is the distance of Earth from the sun, or 150 million km). That means that if you're from a world whose orbit around its star is not 1 AU in radius (like say, Vland, or Zhdant), the distance at which you'll get 1 second of arc is not going to be 3.26 ly.
 
I've never figured out if Traveller uses parsec for the mapping distance as the distance across a hex or the distance in any direction from the mainworld. If it's the second, then the distance across a hex would be double. Parsec is a terro-centric term that would most likely disappear if we ever made contact with other space-faring intelligent life forms - the same for astronomical unit (AU is the distance from the earth to the sun)

Dameon
 
Originally posted by Sir Dameon Toth:
I've never figured out if Traveller uses parsec for the mapping distance as the distance across a hex or the distance in any direction from the mainworld.
It's the distance from the centre of one hex to the centre of an adjacent hex in one of the six "cardinal directions".

Which is interesting, because while a subsector is 10 hexes from top to bottom (coreward to rimward), if you go orthogonally from that in a Trailing to Leading direction, the width of each hex row is actually 0.866 parsecs, not 1 pc. This is because the line connecting the centres of the adjacent hexes is actually the hypotenuse of a right-angle triangle, which is 1 pc long. Since the angle from vertical is 60 degrees, the sideways component of that is (1 * sin 60), which is 0.866 pc. That's an just artefact of using a hex-based system.

So a subsector map really shows an area that is 10 pc long in the core/rim orientation, and 6.928 pc wide in the leading/trailing direction.

A 'square' based alternative would have adjacent systems being 1 pc apart in the core/rim/trailing/leading directions, but a consecutive system diagonally across from the central square would actually be 1.414 pc away (because it's a diagonal - the length of the hypotenuse of a triangle with the other two sides as 1 pc is (SQRT 2), which is 1.414 pc).

I talk about this a little bit in section 2 of my Realistic Near Star Mapping page
 
I always felt the maps should be 10 wide, 8 tall... maintianing the vertical grain.
 
Originally posted by Sir Dameon Toth:
[QB]Parsec is a terro-centric term that would most likely disappear...
Daemon,

Sure, if the 57th Century meaning of the word 'parsec' is the same as our 21st Century meaning. Words and their uses change, look at the term 'gay' for example.

IMTU, when Earth developed jump1, they quickly figured out it's furthest range, 'lets see how far she'll go' and pushing the envelope as it were. Oddly enough, that distance turned out to be somewhere in the neighborhood of a parsec - give or take a few dozen AUs or a couple hundred million miles or so. The term parsec then gradually came to mean the maximum distance you could jump and the old meaning gradually gave way to the new meaning.

I'm sure the first, square-jawed, full of themselves, FTL crews aboard any USSF and ESA jump craft used idiotic NASA-like acronyms for the distance, stuff like MARIF - 'maximum achievable range in flight', or FCD - 'furthest controlled displacement', or whatever else their tiny bureaucratic minds could torturously devise in order to sound important. Remember, these are the same folks who call a zipper an interlocking slide fastener. However once real people began jumping about, they ditched all the NASA-speak for something far simpler - the parsec.

Thus 'parsec' slowly came to mean something entirely different than a parallel arc second. Sure, purists, pedants, cranks, and the like squealed about it, just as purists, pedants, cranks, and the like squeal about any other changes in language. Who cares? People were going to use the word 'parsec' in this new fashion despite what the OED or Immortals have to say on the matter.


Have fun,
Bill
 
Yep, I'm with milord Whipsnade on this. The definition is a word that has changed over time and use. The only difference is imtu it's based on the average displacement rather than the maximum. J1 averaging about 1 old parsec (between 0.5 parsecs and 1.5 parsecs) in safe operation (the extremes not being all that safe to do). The only reason the term sticks at all (like so many Terran terms and Galanglic itself) is due cheifly to the impact of The Rule of Man. I'm sure the Vilani had another term before that to describe the range of J1, and it is probably still used in some circles and is a word in Old High Vilani with a quite different meaning.
 
Yes, just like the word "mile" and "kilometre" have changed their meaning over the years too. Oh wait, they haven't. :rolleyes:

Bill's frothing, contemptuous, venomous rant about NASA aside (I can't think what NASA have possibly done to deserve that), there's no reason for parsec to be changed. It's a specifically defined unit, like miles, kilometres, metres, seconds etc. I'm sure the Vilani would have had different ways to define similarly scaled units too. A Vilani lightyear wouldn't be the same as a Terran lightyear because they most likely have a different unit for a 'second'.

In terms of the game, it's easier to call it a parsec than a 'gikiilishun' or whatever. It makes it more familiar for the reader (though admittedly, I suspect more people know what a lightyear is than a parsec). If you want an in-game explanation for it then most likely what is being presented to us are abstractified Terran-made maps of each sector. Vilani, Aslan, and any other races' maps would probably look rather different.

Also, a parsec is a convenient unit. If you used a lightyear instead, you'd end up with a bloody huge map of the Imperium instead of a merely huge one. Worlds that were right nextdoor to eachother on a pc-scale map would then be several hexes apart on a ly-scale map. Unless you filled the gaps between them with brown dwarfs or dim M star or something.

Or, maybe parsec DID get widespread acceptance. Though it's hard to see why really - metres and kilograms and lightyears and so on can be defined in the same way on any planet. But a parsec is a distance that is specifically defined through observation, and it depends on the size of the planet's orbit. So it would have to be a standardised distance.
 
Well I think "mile" has actually changed (along with many other "standards"), just not in recent history. But that's quite beside the point.

Yes, A "Parsec" is defined but as you noted it's a rather limited Sol-centric definition. But then so is the meter and kg. As you say it's convienient to use familiar (to the players) words and defintions, even if they don't make that much sense in the game. That's all I see here. An in game speculation on why the term survives.
 
Originally posted by far-trader:
Yes, A "Parsec" is defined but as you noted it's a rather limited Sol-centric definition. But then so is the meter and kg. As you say it's convienient to use familiar (to the players) words and defintions, even if they don't make that much sense in the game. That's all I see here. An in game speculation on why the term survives.
It's probably just better not to think about it ;) - any alternatives (like each race having explicitly different measuring systems) would undoubtedly make things massively complicated anyway, even if that would make it more realistic.

Personally, I tweaked the definitions so that J1 actually meant that you could jump to any destination between 0.5 and 1.5 parsecs of your origin point (and the same for J2-J6). At least that way you could have worlds that were not magically exactly an integer number of parsecs apart as they're shown on the map. But you could easily just say they're "jump units" instead of parsecs. Since distance isn't really preserved on the flat maps anyway, it may be a better solution.
 
Yep partly the same reason I came up with J1 can do 0.5 to 1.5. It also helps when doing off angle jumps. Like 2 hexes over and 1 up is J3, being between 2.5 and 3.5 rather than exactly 3.0 which it isn't. I like the idea of just calling them "jumps" or "jump units" instead just fine. It's usually how they are used anyway by the players and ref. "System X is J3 and System Y is J4" rather than "Sytem Z is 2 parsecs, or about 6.52 light years." We still need to know what we are talking about in distance but for usage I think most spacers would be doing it the way we have, "Oh, you're from there, that's just J1 from my homeworld, hey maybe you know... " ;)
 
Originally posted by Malenfant:
[QB] Yes, just like the word "mile" and "kilometre" have changed their meaning over the years too. Oh wait, they haven't. :rolleyes:
Dr. Thomas,

Check out the history of the word 'mile' in the OED, you may actually be surprised.

Bill's frothing, contemptuous, venomous rant about NASA aside...
Now, now, now, we two aren't supposed to type things like that about each other. Remember Hunter's warning to us both? Hmmm?

Languages change and the words that make up them change. It works IMTU, it's nonsense IYTU, and it doesn't really matter anyway.


Have fun,
Bill
 
Originally posted by Larsen E. Whipsnade:
</font><blockquote>quote:</font><hr />Bill's frothing, contemptuous, venomous rant about NASA aside...
Now, now, now, we two aren't supposed to type things like that about each other. Remember Hunter's warning to us both? Hmmm?
</font>[/QUOTE]Yes. And that doesn't change the fact that you were frothing, contemptuous, and venomous. I wasn't the one who suddenly and for no apparent reason launched into a foul tirade against people who would work at NASA when it wasn't even relevant to the discussion.

I'd wager you don't even know people who work there - I do. For that matter, I've met astronauts too. And while the bureaucrats and politicians there may be somewhat small-minded, most of the rest of the people - including the ones who would potentially be flying the ships that you were so bile-filled at - are good, sensible people.

So kindly leave your vitriolic rants about NASA out of this.
 
Actually, it isn't all that bile filled, and many of NASA's acronyms and terminologies are, well, part of the paradigm of the military space programs NASA partially included when being formed.

His choice of words was "Colorful"; I find your tone over it equally, if not more so, vitriolic, Mal.

The post seemed to me to be an "In milieu" history. I laughed on first read.

Knowing the people doesn't make the excessive acronym usage any less idiotic, for both crypticness and unpronouncability. It is understandable, but not a bright thing in many people's opinion. (in part, it is an artifact of the typewriter and handwriting as opposed to word processing, and also in part a tradition of military programs and secrecy issues.)
 
All that may be true, but it's one thing to point that out and another to go on about it the way Bill did. From his tone, you'd be forgiven for thinking that NASA had committed some unspeakable violation upon his person.

It's true that I don't have high tolerance for Bill, particularly when he gets all bitter and twisted about something (and I've been on the receiving end of that myself). When he gets like that his posts are just plain toxic. How anyone can get so twisted about things that are basically not really all that important is beyond me.
 
Originally posted by Malenfant:
When he gets like that his posts are just plain toxic. How anyone can get so twisted about things that are basically not really all that important is beyond me.
"You really do walk into these things don't you Baldrick?" - from Blackadder the Third, "Sense and Senility"

Like about CT chargen for example?

(Casey has been watching Blackadder a lot of late)
 
Sarcasm, Mal. Sarcasm.

Bill (and often I) are filled with it. We use it for humor. It carries poorly on paper (or other textual media).

Bill tends to exaggerate his dislikes for humorous intent (or, more correctly, apparently for same). I do, too.

But it is easily mistaken for vitriol. There are a few things that raise my hackles rather quick...

As for NASA commiting an unspeakable Violation, well the promised lunar colony is STILL not there, Pan-Am is a shade of it's former self, and NASA can't keep the fleet flying, rejected Both the serious contenders claiming the shuttle was good enough, and fills it's papers with unreadable jargon, despite knowing that educators are the most common readers, and typically are of average to subaverage IQ's based upon studies.

I don't disparage my own colleagues lightly, but many aren't PLAYING a box of rocks, but ARE a box of rocks. (One is even quite good at teaching her grade level, despite being by her own admission, far from the sharpest tool in the shed.) Whoops, a bit of sarcastic exaggeration again!

NASA is lofty in it's mission, but has failed on promise after promise; it's losing street cred. NASA at one point said we'd be colonizing the moon within the next five years... we can't even send a man there now! (Actually, we could, by sending a few of russian energia launchers up... one with the orbiter, one with the lander, one with a landable base, and a Soyuz up to send the crew up. The assembled craft could use some chem with a few ion arrays to shorten travel times..

NASA is, in short, dedicated to keeping NASA in the business of being NASA, as opposed to actually exploring space by human means, which was why they were formed: too put men into space to learn about earth.

more than 10 astronauts are dead because of complacency in NASA at some level, rather than ignorance, ala Apollo 1. A spaceprobe was lost because someone forgot to label units on a program's interface. (both shuttle losses were foreseeable incidents that administrators decided were too small a threat to fix. Or, for that matter, to check for.)

But, back on topic:
A traveller parsec is a unit of hyperspace distance which apparently correlates closely to the distance of 1 arc second of parallax of earth's orbit.
 
Originally posted by Aramis:
[QB] Sarcasm, Mal. Sarcasm.

Bill (and often I) are filled with it. We use it for humor. It carries poorly on paper (or other textual media).

Bill tends to exaggerate his dislikes for humorous intent (or, more correctly, apparently for same). I do, too.
I can tell sarcasm apart from malice. And in Bill's case, when he gets on his high horse he's all about the sheer spite and malice, not sarcasm.
Hell, he practically wished me dead for approving of bioroids in Transhuman Space, because the concept offended him so. And this is something in a freakin' game.


As for NASA commiting an unspeakable Violation, well the promised lunar colony is STILL not there, Pan-Am is a shade of it's former self, and NASA can't keep the fleet flying, rejected Both the serious contenders claiming the shuttle was good enough, and fills it's papers with unreadable jargon, despite knowing that educators are the most common readers, and typically are of average to subaverage IQ's based upon studies.
Yes, and none of that affects anyone personally. Unless they had their entire future staked on the fact that they'd be living on the moon by the year 2000, or were one of the people laid off when the X-(34?) was cancelled.

It's fine to be annoyed at that - I sure as heck am. I thought Sean O'Keefe and Dan Goldin - the former NASA administrators - made a lot of stupid, incomprehensible decisions. NASA is just blundering around in the dark today.

NASA is lofty in it's mission, but has failed on promise after promise; it's losing street cred. NASA at one point said we'd be colonizing the moon within the next five years... we can't even send a man there now! (Actually, we could, by sending a few of russian energia launchers up... one with the orbiter, one with the lander, one with a landable base, and a Soyuz up to send the crew up. The assembled craft could use some chem with a few ion arrays to shorten travel times...
It's funny how every scifi/space fan thinks they can do a better job
. There's a lot of bureaucracy and politics in all this. It shouldn't be there, but it is. That's what's messing things up. That and a lack of focus and money and resources.

Plus, it's hard to send people to Mars and the Moon when it requires billions to be spent on research and engineering over several decades, and successive US governments come along and 'rethink' it all every four years and scrap this and that and change priorities. Bush's insane Moon/Mars program won't last for the same reasons - it's very badly thought out, it makes a lot of rather optimistic assumptions, is shafting most of the astrononomical community by shifting the focus to manned flight when perfectly good unmanned missions (like Hubble) are being screwed over, and frankly most of the astronomical community doesn't actually see the point of it either.


NASA is, in short, dedicated to keeping NASA in the business of being NASA, as opposed to actually exploring space by human means, which was why they were formed: too put men into space to learn about earth.
Funny, I thought they were formed to try to beat the Russians into space ;) .


more than 10 astronauts are dead because of complacency in NASA at some level, rather than ignorance, ala Apollo 1. A spaceprobe was lost because someone forgot to label units on a program's interface. (both shuttle losses were foreseeable incidents that administrators decided were too small a threat to fix. Or, for that matter, to check for.)
Oh, Apollo 1 was complacency and idiocy too. Yes, these cases were avoidable and caused by bureaucratic dithering, but don't be under the illusion that space travel is or ever will be 'safe'. It's always going to be a risk.
 
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