![Image](http://www.astrobio.nau.edu/~koerner/ast180/lectures/pic/cdrom/art_high-res/ch02/figure-02-08.jpg)
ellipse focus question
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- Ensign
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- AKA: mud
- Location: New Mexico, USA
ellipse focus question
So, I'm too ignorant to know if this person's idea is misguided, so I'm asking, to find out. The person said that, if the sun is a focus of a planetary ellipse, something else has to be a focus on the other side of the ellipse. Intuitively, this feels wrong to me, probably because I play with yo yos and the like. The person said the phantom or ghost ellipse is dark matter, but i'm thinking it's just not there. SO? :/
![Image](http://www.astrobio.nau.edu/~koerner/ast180/lectures/pic/cdrom/art_high-res/ch02/figure-02-08.jpg)
![Image](http://www.astrobio.nau.edu/~koerner/ast180/lectures/pic/cdrom/art_high-res/ch02/figure-02-08.jpg)
- neufer
- Vacationer at Tralfamadore
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Re: ellipse focus question
The answer is contained within the posted diagram:rriverstone wrote:
The person said that, if the sun is a focus of a planetary ellipse, something else has to be a focus on the other side of the ellipse. Intuitively, this feels wrong to me, probably because I play with yo yos and the like. The person said the phantom or ghost ellipse is dark matter, but i'm thinking it's just not there. SO? :/
There is NOT a symmetry between the two foci:
equal areas are circumscribed in equal times ONLY as regards the sun focus.
Art Neuendorffer
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Re: ellipse focus question
I thought so. The real focus is the sun. The secondary position in the ellipse, while it may be CALLED a "focus," does not require a body with mass, gravity, etc. for the elliptical orbit to function. Having rolled pennies in those giant funnel thingies in malls, I didn't think a 2nd object was necessary. Water goes down my bath tub drain without another hole at the other end, too.
I hope i understood your answer. thx
I hope i understood your answer. thx