RE: [APML] Image Brightness (was Color of Objects (was Astronomy Magazine M8))

[Matt BenDaniel <matt@starmatt.com>]

At 10:24 PM 12/7/2001 -0800, Richard Klappal wrote:
>...
>Is a globular cluster/galaxy/etc an extended object?  Or is it a collection
>of point sources?  Which set of assumptions/formulae apply?  Just because we
>have an unresolvable collection of point sources, or overlapping Airy disks,
>do they stop being points and now act as an extended object?
...

Yes, if the airy disks overlap and fill an area of film, the object acts as an extended source. Galaxies are perceived as extended sources, but they consist mostly of point sources (i.e. stars). 

But a distant supernova appears as a point source. It stands out because its brightness is way over the neighboring stars'.

I think a globular cluster is seen as a combination of both individual sources and as an extended source. The stars are easier to resolve at the edge. An example:
http://people.ne.mediaone.net/mbendaniel/gallery/astro/omega_centauri.html

Photographically I treat a globular cluster as an extended source, but it does have quite a bit of dynamic range. Print film is better for globulars than is slide film.
--
Matt BenDaniel
http://starmatt.com


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