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

["Marc \"Zeke\" Kossover" <zeke_kossover@yahoo.com>]

I couldn't figure out what was going on until I noticed the unit change in the first line compared to other lines.

1 AU = 150   x 10^9 m
1 LY =    9.5 x 10^15 m

So a light year is a touch larger than an astronomical unit.

Then the subtended arc also changes units but not so dramatically, but it does use degree:minute:second notation which is just so Babylonian. 

So, the first object creates a subtended angle of 3.6 x 10^-6 degrees and the second subtends an angle of 49274 x 10^-6 degrees (or 0.049 degrees), assuming my math is correct. While the first object is much closer it is much, much smaller so that it looks much, much smaller than the the far, far away object.

Astronomers what can you do with them? :)

Zeke Kossover


----- Original Message ----
> From: Brian Whatcott <betwys1@sbcglobal.net>
> To: Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu>
> Sent: Thursday, February 19, 2009 5:20:58 PM
> Subject: Re: [Phys-l] Figuring Physics in the March TPT The Physics Teacher
>
> Bill Nettles wrote:
> > .....
> > 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).
> I read this passage twice, and it means as much to me now as before I 
> read a word.
> So this is how decrepitude begins? :-)
>
> Brian W
>
>
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