Re: APOD: Polar Ring Galaxy NGC 2685 (2014 Mar 14)
Posted: Mon Mar 24, 2014 3:46 am
(And owlice, I think you are right about lentils giving their name to the lens shape. Thank you for setting me straight.)
APOD and General Astronomy Discussion Forum
https://asterisk.apod.com/
Note that either one of those shapes is quite correctly described as lenticular.Nitpicker wrote:I did even less to turn your lens into a more realistic oval/lenticular football. But there is definitely still a need for the concept of the sharp lens shape, I just don't think it should be related to football.
(And owlice, I think you are right about lentils giving their name to the lens shape. Thank you for setting me straight.)
Agreed. Also, the left one could be just as correctly described as oval, or an oval. And whilst oval and lenticular do not have precise definitions, lens does, and only the one on the right side is a lens.Chris Peterson wrote:Note that either one of those shapes is quite correctly described as lenticular.Nitpicker wrote:I did even less to turn your lens into a more realistic oval/lenticular football. But there is definitely still a need for the concept of the sharp lens shape, I just don't think it should be related to football.
(And owlice, I think you are right about lentils giving their name to the lens shape. Thank you for setting me straight.)
Nope, both are lenses. Lenticular has a precise meaning: shaped like a lens. And when referring to shape, lens just means biconvex. There is no constraint on either symmetry or the structure of the intersection between the two curves (which need not be circular).Nitpicker wrote: Agreed. Also, the left one could be just as correctly described as oval, or an oval. And whilst oval and lenticular do not have precise definitions, lens does, and only the one on the right side is a lens.
In that case, we are back to having no word for the shape of the intersection of two circles. But, nope, I think lens actually does have a precise meaning in a geometric context:Chris Peterson wrote:Nope, both are lenses. Lenticular has a precise meaning: shaped like a lens. And when referring to shape, lens just means biconvex. There is no constraint on either symmetry or the structure of the intersection between the two curves (which need not be circular).Nitpicker wrote: Agreed. Also, the left one could be just as correctly described as oval, or an oval. And whilst oval and lenticular do not have precise definitions, lens does, and only the one on the right side is a lens.
The existence of a very formal mathematical definition doesn't invalidate other, much more common definitions. Also useful, lens and lenticular are equally applicable to both 2D and 3D structures. So in the context of galaxies, they could refer to either the actual shape or to the shape in projection. (Of course, lenticular is also a galaxy classification, so there could be some confusion, given that many elliptical galaxies can be described geometrically as lenticular.)Nitpicker wrote:I think lens actually does have a precise meaning in a geometric context:
http://en.wikipedia.org/wiki/Lens_(geometry)
It is no more formal than the definition of a square, circle, ellipse, rectangle, etc. I think the difference is that it is not as well known. See also:Chris Peterson wrote:The existence of a very formal mathematical definition doesn't invalidate other, much more common definitions. Also useful, lens and lenticular are equally applicable to both 2D and 3D structures. So in the context of galaxies, they could refer to either the actual shape or to the shape in projection. (Of course, lenticular is also a galaxy classification, so there could be some confusion, given that many elliptical galaxies can be described geometrically as lenticular.)Nitpicker wrote:I think lens actually does have a precise meaning in a geometric context:
http://en.wikipedia.org/wiki/Lens_(geometry)