Re: [Phys-L] Solar eclipse (by Phobos) as seen by Perserverence rover

[Brian Whatcott <betwys1@sbcglobal.net>]

 I have been thinking that homework is not what it used to be. Google and all that - on a plate.So reading Todd's piece, I thought to give it a try.
Scratch up some factsPhobus 11 km mean diameterOrbital distance 6000 km from Mars surfaceOrbital period 7 hrs 39 min. = 459 min.
Sun diam 1392 10^3 kmSun distance  228 10^6 km  (Actually 206 to 249 10^6 km)
Say Phobus subtends angle of atan 11/6000 degrees = 0.10504 deg from MarsSay Sun subtends angle of  atan 1392 / 228000 deg = 0.3498 deg
Define eclipse to be region from first contact to last contact.This angle is 0.3498 + 0.10504 deg = 0.45484 degThis takes  0.45484 * 459 / 360 min. = 0.58 min or 34.8 seconds
But the video eclipse takes 35 seconds according to its graticule.So it looks like a reasonable ball-park answer can be found  despite the data liberties that I tookwith scratching up Google numbers.    On Friday, April 22, 2022, 03:10:16 PM CDT, Todd Pedlar via Phys-l <phys-l@mail.phys-l.org> wrote:  
 
 who's propositioning the rover?  OH... you said PRE-positioning! :)

Indeed.  That photo is going on a homework problem in the Fall, asking
students to determine, assuming phobos is tracking horizontally across the
image, a) the orbital distance of phobos given its dimensions and the
diameter of the sun, and b) the length of eclipse in time given the result
for part a and Newton's LUG.  I'll let them assume
circular orbit (eccentricity is 0.015 so it's not that bad).  If I wanted
to push it harder, I'd not let them assume circularity in calculating
the length of the eclipse in time but make them use the actual eccentricity
in doing the problem :)

On Fri, Apr 22, 2022 at 12:26 PM David Bowman <
David_Bowman@georgetowncollege.edu> wrote:

> Here is a NASA video of an annular eclipse of the sun by Phobos as
> recorded by the Perserverence rover on Mars.  It's a couple of days old.
> That's some pretty impressive prepositioning of the rover to get that shot.
>
> https://youtu.be/aKK7vS2CHC8
>
> David Bowman
> _______________________________________________
> Forum for Physics Educators
> Phys-l@mail.phys-l.org
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-- 
Todd K. Pedlar
Professor of Physics and Physics Department Head
Luther College, Decorah, IA
pedlto01@luther.edu
(563) 387-1628
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