Okay, I realise now that a "perfectly circular orbit" is actually
possible to achieve, although not easy to maintain - and certainly
extremely difficult to occur naturally!
I learned in A-level Physics that, say, the Moon orbits the Earth in an
oval-shaped orbit, with the Earth at one focus of the oval. I'm not
quite sure I remember what a "focus" is in geometry, but I think it's
something along these lines (physicists and geometry experts, move the
mouse pointer to "Reply to Sender" and stand by):
Take two pieces of string of equal length, and attach them to the paper
with drawing pins, a distance apart equal to or less than the length of
each piece of string (say you have 2 pieces of string of 10cm., stick
them in at or less than 10cm. apart). Then tie both free string ends to
a pencil (of course, you need 10cm. length of each string left after all
this tying and pinning is done... oh, you get the idea! And the
string's gotta be inextensible!). Now, you draw as big an oval as you
can without yanking the string out or anything (and with the pencil
vertical). You end up drawing an oval, and the two drawing pins are the
two foci. Is that right, please? I presume, then, that a "perfectly
circular orbit" merely has the two foci overlapping.
Which makes me wonder: is there another foci in an elliptical orbit?
Say, when the Earth is in its elliptical orbit (as happens
periodically), is there... another mass acting as the other foci, which
we can't see? Does the orbit itself lead to this other mass being
formed? Could this be the "dark matter" we're searching for? Or is
this just another example of lousy science?
Sorry, I'll shut up for now. And yes, I know it's spelled "esoteric" -
I was misled by an earlier occasion on which I spelled it "isoteric" (I
was younger and more foolish then).
D.Chilard
possible to achieve, although not easy to maintain - and certainly
extremely difficult to occur naturally!
I learned in A-level Physics that, say, the Moon orbits the Earth in an
oval-shaped orbit, with the Earth at one focus of the oval. I'm not
quite sure I remember what a "focus" is in geometry, but I think it's
something along these lines (physicists and geometry experts, move the
mouse pointer to "Reply to Sender" and stand by):
Take two pieces of string of equal length, and attach them to the paper
with drawing pins, a distance apart equal to or less than the length of
each piece of string (say you have 2 pieces of string of 10cm., stick
them in at or less than 10cm. apart). Then tie both free string ends to
a pencil (of course, you need 10cm. length of each string left after all
this tying and pinning is done... oh, you get the idea! And the
string's gotta be inextensible!). Now, you draw as big an oval as you
can without yanking the string out or anything (and with the pencil
vertical). You end up drawing an oval, and the two drawing pins are the
two foci. Is that right, please? I presume, then, that a "perfectly
circular orbit" merely has the two foci overlapping.
Which makes me wonder: is there another foci in an elliptical orbit?
Say, when the Earth is in its elliptical orbit (as happens
periodically), is there... another mass acting as the other foci, which
we can't see? Does the orbit itself lead to this other mass being
formed? Could this be the "dark matter" we're searching for? Or is
this just another example of lousy science?
Sorry, I'll shut up for now. And yes, I know it's spelled "esoteric" -
I was misled by an earlier occasion on which I spelled it "isoteric" (I
was younger and more foolish then).
D.Chilard