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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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