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Re: Introducing the United (fps) System
Posted:
May 4, 2000 6:25 PM
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Gene Nygaard wrote in message <8ehbg6$9r8$1@nnrp1.deja.com>...
>In article <GB4PItAQduC5EwNS@earthpoetry.demon.co.uk>,
> rc@earthpoetry.demon.co.uk wrote:
>> In article <390adc8a.3278162@news.nccray.com>, Gene Nygaard
>
>> >
>> >With SEVEN significant digits? Get real.
>> >
>> >Alpha Centauri might be 41 Pm away.
>> >
>> Chill out. It was only done for effect. Imagine the line of metres.
>> 41 Pm =c metres.
>
>If that was your goal, there is still a sizable group of astronomers who
>cling to an old metric system as tenaciously as the American public
>clings onto their miles. To them, this distance should be expressed in
>the ideal metric units for the distance between stars (they'd normally
>use scientific notation, of course) as
>
> 4 100 000 000 000 000 000 cm
>
>They also think that ergs per second are the ideal units for measuring
>the power of stars, etc.
>
>--
>Gene Nygaard
>http://ourworld.compuserve.com/homepages/Gene_Nygaard/
>
>
>Sent via Deja.com http://www.deja.com/
>Before you buy.
Does anyone know why that is? I have an an astronomy and cosmology book from
the '60s which states stellar masses in grams, distances in cm, and power in
ergs/s. A more recent book by Alan Guth also uses these for large measures.
Surely astronomers don't go look for lightbulbs rated in ergs per second.
Why do they use these units for large measures?
Of course, I don't believe these units should be discarded and replaced with
SI, but instead they are only appropriate for small things. On my desk I use
a centimeter ruler. I use meters for larger things. I use grams for things
which are hand sized, and kg for larger. I use watts for most power
measures, and joules for energy. I would use ergs in the right situation.
Why do astronomers use these?
David C. Baker
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