Re: [office-formula] Straw poll - slug (and lightyear)

[Eike Rathke <erack@sun.com>]

Hi Patrick,

On Friday, 2010-04-09 10:48:24 -0400, Patrick Durusau wrote:

>>> If we say a light-year is the "distance light travels in a vacuum in 1
>>> Julian Year, which is 365.25 days" then this may be very correct but
>>> also very useless. Implementors will still need to decide what that
>>> value really is (or at least which value to use).
>>>
>>> On the other hand if we have exact conversion factors in the OpenFormula
>>> standard to convert all those distance units into meters, then the
>>> conversion between any two distance units becomes obvious.
>>>      
>> +1
>>
>> Let's state the conversion factor, and additionally have that
>> explanation.
>>
>>    
> OK, which explanation?
>
> I now have:
>
>> Light-year, the distance light travels, in a vacuum, in a year of  
>> 365.25 days

Insert Julian for clarity:
Light-year, the distance light travels, in a vacuum, in a Julian year of
365.25 days

> Conversion factor? Ok, I had to get up out of my chair but:
>
> light year ly = 9.460530 X 10^17 cm
>
> Source: Kenneth R. Lang, Astrophysical Data, Springer-Verlag, 1992.

Hm.. OOo currently has the factor 1m = 1.0570234557732930E-16 ly, that
would be 1 ly = 9.460528 x 10^15 m, though I don't know where that
originated.

We have speed of light c = 299792458 m/s, a Julian year is
365.25 days that are 31557600 seconds, that would give
1 ly = 299792458 m/s * 31557600 s = 9.4607304725808E+15 m
or 1 m = 1.05700083402462E-16 ly.

Confusing.

> Would it be better to state it in centimeters?

No, in meters please ;-) that is the scientific unit.

> Hope you are looking forward to a great weekend!
>
> Patrick
>
> PS: I can also insert more exact measurements for Astronomical Unit,  
> Parsec and Megaparsec if anyone is interested.

OOo currently has 1m = 3.240779E-17 pc

http://www.metas.ch/metasweb/Themen/Masseinheiten/calculation/en_calculation_frame_umrechnungen.html
says

1 pc = 3.085678 × 10^16 m = 3.085677581E+16 m
1 m = 3.240779 × 10^-17 pc = 3.24077928996043E-17 pc

1 UA = 1.495979 × 10^11 m = 149597870700 m
1 m = 6.684587 × 10^-12 UA = 6.68458712226845E-12 UA

I think no one gets that more accurate than an institution of the
"Schweizerische Eidgenossenschaft" ;-)

Note that we currently don't define Astronomical Unit because of
disagreements over its exact value (+-30m) and the name of the symbol,
see also under Distance in the Rationale text of CONVERT.

The International Astronomical Union (IAU) isn't much helpful in this
regard, it is supposed to define UA, but for the conversion it just says
length  astronomical unit  au  0.149 598 Tm
in http://www.iau.org/science/publications/proceedings_rules/units/
Table 5. Non-SI units that are recognised for use in astronomny.
[actually also their parsec conversion is quite sloppy with 1pc = 30.857Pm]

http://en.wikipedia.org/wiki/Astronomical_unit says the IAU accepted
a best estimate of 1UA = 149597870700m, which is also what the Metas
converter says.

  Eike

-- 
Automatic string conversions considered dangerous. They are the GOTO statements
of spreadsheets.  --Robert Weir on the OpenDocument formula subcommittee's list.

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