Re: [Phys-L] Trick photography?

["Bob Sciamanda" <treborsci@verizon.net>]

Here's a reference to the "actual vs. apparent" moon motion:
http://cseligman.com/text/sky/moonmotion.htm

-----Original Message----- 
From: Bob Sciamanda
Sent: Sunday, March 02, 2014 12:45 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] Trick photography?

Thanks, John!  I'm going to have to bone up on the "actual vs. apparent"
moon velocity.  This distinction never occurred to me. Thanks for the info!
-Bob

-----Original Message----- 
From: John Mallinckrodt
Sent: Sunday, March 02, 2014 12:25 PM
To: Phys-L@Phys-L.org ; Bob Sciamanda
Subject: Re: [Phys-L] Trick photography?

Because the human motion is completely natural and the Moon takes (125±1)
seconds to move its own diameter as it should, the movie certainly shows the
motions correctly.  But equally obviously, the people don't move 100 times
as fast as the moon, its more like a factor of 3 or 4.  It took me awhile,
but I finally realized that your mistake was in using the moon's "actual
velocity" (3356 ft/s) rather than it's "apparent velocity" (87,000 ft/s).
remember that the moon *apparently* goes once around its orbit in about 25
hours.

With that correction we get u/U = 4

John Mallinckrodt
Cal Poly Pomona

On Mar 2, 2014, at 7:36 AM, Bob Sciamanda wrote:

> To answer several queries, the calculation I meant to suggest might go
> something like this ==>
>
> Notation:
> V = speed of moon in its orbit
> v = speed of person walking on earth
> D = moon-lens distance
> d = person-lens distance
> f = camera lens focal length
> U = speed of moon image across film
> u = speed of image of walking person across film
>
> Optics:
> U = (f/D)V
> u = (f/d)v
>
> ==> u/U = (D/d)(v/V)
>
> Data:
> D = 1,246,720,000
> d = 6890 ft
> V = 3356 ft/sec
> v = 2 ft/sec
>
> Result:
> u/U = 108
> ie., The walking person's image should move across the film about 108 
> times
> as fast as the moon's image moves across the film.
>
> Please improve, and correct any boo-boos - and do it in metric units ; )
>
>
> -----Original Message----- 
> From: Bob Sciamanda
> Sent: Saturday, March 01, 2014 11:24 AM
> To: PHYS-L
> Subject: [Phys-L] Trick photography?
>
> If you’ve never seen a tele-video of a distant terrestrial scene 
> silhouetted
> by a rising moon, look at==>
> http://vimeo.com/58385453.
>
> The casual observer often complains that this must be a manipulated
> photoshop type trick.
>
> It is an interesting exercise for students to investigate this by
> calculating, and comparing, the speeds of the terrestrial and lunar images
> across the camera film/digital sensor.
> More than sufficient data is available from the video clip, its 
> commentary,
> and known lunar data.
>
> Bob Sciamanda
> Physics, Edinboro Univ of PA (Em)
> treborsci@verizon.net
> http://sciamanda.com
> _______________________________________________
> Forum for Physics Educators
> Phys-l@phys-l.org
> http://www.phys-l.org/mailman/listinfo/phys-l
>
> Bob Sciamanda
> Physics, Edinboro Univ of PA (Em)
> treborsci@verizon.net
> http://sciamanda.com
>
> _______________________________________________
> Forum for Physics Educators
> Phys-l@phys-l.org
> http://www.phys-l.org/mailman/listinfo/phys-l

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Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
treborsci@verizon.net
http://sciamanda.com

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
treborsci@verizon.net
http://sciamanda.com