Re: [Phys-l] Figuring Physics in the March TPT The Physics Teacher

["John Clement" <clement@hal-pc.org>]

Yes, he doesn't use any data to figure the subtended angle, so while it
depends on the distance, it also depends on the size of the object.  It
turns out that basketball at 2m subtends a larger angle, but that has not
been shown.  It is very unclear.

I also consider the reverse perspective to be unclear to many because
perspective as far as I know is not in any physics courses, except perhaps
as a footnote.  It is not wrong, just very unclear.

John M. Clement
Houston, TX

> -----Original Message-----
> From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
> bounces@carnot.physics.buffalo.edu] On Behalf Of Bill Nettles
> Sent: Thursday, February 19, 2009 11:54 AM
> To: Forum for Physics Educators
> Subject: Re: [Phys-l] Figuring Physics in the March TPT The Physics
> Teacher
>
> Okay, now I see it. I still think the diagram is poorly made, but the end
> of the first sentence should say, "depends (as a first approximation) on
> the ratio of the sphere's diameter to the distance from the sphere." or
> something like that.  Yeah, subtended angle (which is what he highlights
> in the 2nd sentence) depends on more than distance.
>
> Bad Astronomy had a good picture of a planetary nebula that was 2 AU
> across at a distance of 500 LY.  It was kind of fuzzy, not nearly as
> pretty as some Hubble pictures of other planetary nebula, but they were
> 4.3 LY across at 10000 LY distance. but when you compare the angular
> sizes, the quality of the first becomes dramatically impressive (13
> milliarcseconds versus 1.5 arc-minutes).
>
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