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Thanks to all for a most informative discussion.

Just to let you know, I contacted a mathematician at the University of
Waterloo Department of Pure Mathematics to pose this question. He didn't
even bat an eye at the idea of some crackpot from the netherworld asking for
obscure information. Unfortunately, he did not have an answer but he
promised to run it by his colleagues and get back to me. I in turn, will
report back to the list if I get an answer other than the ones provided. He
did, however, suggest that "steradian" may be an appropriate description.

Robert


----- Original Message -----
From: "Alexandre E Eremenko" 
To: 
Sent: Thursday, March 30, 2006 4:08 PM
Subject: Re: Mathematics Question


> Dear Robert,
>
> It is possible that I misunderstood your question.
> It was not clear whether you asked about "arc" or
> about "arc measure".
>
> For a mathematician, an arc is a geometric object, a set,
> something you can see. "Arc measure" is just a number.
>
> It is like a difference between the lot of land on which your
> house stands and the number which is how many acres are
> in this lot of land. Or the difference between you, yourself,
> and your height:-)
>
> The set itself (=the geometric object, the piece of the sphere)
> in 3 dimensions is called variously a "cap" a "cup" or "sperical disc".
> Its SIZE is measured in square radians and called the "solid angle"
> as many list members pointed out.
>
> Thunk of the sentence "this cap has the solid ange of 0.0003 square
> radians"
> as an analog of the sentence "this lot has the area of 1.25 acres".
>
>
> Alex.
>
>> On Wed, 29 Mar 2006, Robert Eno wrote:
>>
>> > A math question for list:
>> >
>> > Given that a segment of a circle
>> > is called an "arc", can anyone
>> > tell me what its two-dimensional
>> > equivalent on a sphere is called?
>> >
>> > Robert
>> >
>>
>>

   

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