Subject: SI prefixes (was Re: What ius [sic] a parsec?)

From: [email-masked] (Erik Max Francis)
Date: Fri, 04 Jun 93 03:19:30 PDT

[email-masked] (Roland Karlsson) writes:

> All those conversion factors just disappears if you stop using archaic
> units (:-) like lightyears, parsec, au, feet, inch, ounce, gallon,
> mile, nautical mile, knot, etc.  Use the metric system.  Much more
> convenient.  How about using giga-km or tera-km for astronomical
> distances, just as micro-meter or nano-meter for the very small ones?

Definitely, though I'd qualify your use of the term "metric" to 
specifically mean SI, instead of more conventional meanings of the term 
"meric."  Meters, kilograms, seconds, amperes (and other supplementary 
units).  Who could ask for more?

Though I think gigameter and terameter would be more fluid and useful 
(and they're already being used) than giga-kilometer and tera-kilometer, 
as that's just a terameter and a petameter, respectively.

Anybody catch the article in _Science News_ about the extra drafted 
official SI prefixes?  They were zempto-, yatto-, and two other analogous 
ones for the opposite end of the spectrum.  Very, very interesting.  Is 
this _really_ official or what?

Erik Max Francis, &tSftDotIotE ...!apple!uuwest!max [email-masked]  __
USMail: 1070 Oakmont Dr. #1  San Jose, CA  95117  ICBM: 37 20 N  121 53 W /  \
If you like strategic games of interstellar conquest, ask about UNIVERSE! \__/
-)(- Omnia quia sunt, lumina sunt.  All things that are, are lights. -)(-

---

From: [email-masked] (Erik Max Francis)
Date: Tue, 08 Jun 93 04:14:45 PDT

[email-masked] (richard d clark) writes:

> I suppose this would work as long as they add enough prefixes. What power
> 10 is the new&improved highest?

I wish I knew for sure.  There were four new prefixes, two large and two 
small.  Two started with the letter _y_; the other two started with _z_.
The smaller pair was lowercase, as is the convention -- y & z -- and the 
bigger pair were uppercase -- Y & Z.  The names were something like 
_yatto_ and _zemto_, but I can't remember exactly and I don't remember 
how the large and small names differed, though I remember they were very 
similar.  Other than that, I don't remember anything else that's useful.  I
have the _Science News_ article around here somewhere; I'll try to dig it 
up and post an excerpt if I can.  At any rate, they fill up where exa- 
and atto- leave off:  they take up 10^+-18 and 10^+-21.

> Hmmm... 1 pc is 10 pi tera km. So we can start talking about intergalactic
> distances in megaterakm. Or would that be gigaterameter. Is this the same
> as a yattometer? I've lost count.

A gigaterameter would be 10^9 x 10^12 m = 10^21 m, which _was_ 
represented by the largest new prefix, which, if I recall, was a Y, 
though I don't remember the name.

Damn.  I'm really going to search through my old issues for this thing 
now . . .

> What do peopple think about which would be more convenient: changing the
> basic time unit to one equal to about .1 sec so the day would be 1 mega of

I have actually seen a metric system of time which worked at the day 
level.  Each day was broken down into ten decidays, which were broken 
down into ten centidays, which in tern were broken into ten millidays.  
The roughly equivalent analogue is deciday-centiday-milliday to 
hour-minute-second.  One deciday equals 2.40 hours; one centiday equals 
14.4 minutes; one milliday equals 86.4 seconds (1.44 minutes).

Actually, some institutions already use this system, although they don't 
use it _as such_.  They don't talk about anything smaller than days --
and thus use decimals to represent smaller times -- but don't talk about 
decidays, centidays, or millidays.

> Let's face it, people in any field will use whatever units are 
convenient
> for them. We seem to like for numbers to be 'several' +- 'a few', hence
> the use of kg, km, or kton as if they were a basic unit. Recognition of
> this tendency is official: the unit of volume is the liter and not the
> cubic meter.

That's true, of course.  It'd just be nice if we could all agree on the 
same _base_ system -- such as SI -- to use to get all these standard 
units.  Instead of using inches, feet, miles, or millions of miles, it 
would be nicer (and easier to understand each other) if you'd use an SI 
equivalent like cm, m, km, or Gm.

---

From: [email-masked] (Peter Somlo)
Date: Wed, 9 Jun 1993 00:13:31 GMT

>14.4 minutes; one milliday equals 86.4 seconds (1.44 minutes).

In the Splus language, I have written a function which, when supplied with
the eight digits before the decimal point (for: year, month, day) and with
the four digits after the decimal point (for: hours, minutes), converts this
number into Julian days, with decimal fraction for part-day entries. This
way, accurate chronoligal plots may be produced.

-- 
Dr Peter I. Somlo FIEEE | CSIRO Div. Appl.Phys. | "Every coin has three
Head RF/Microwave Proj. | Natl. Meast. Lab.     |  sides - at least"
FAX: 61-2-413-7383	| POB 218 Lindfield 2070|  (Somlo, cca. 1985)
TEL: 61-2-413-7505      | NSW AUSTRALIA         |