Re: Volcano trail did you know about this...?


Re: Why are the 'Fixed Stars' so FIXED?

Group: sci.astro Date: Sun, Apr 1, 2007, 2:54pm (EDT+5) From:
george@xxxxxxxxxxxxxxxxx (George Dishman)
"Leonard Kellogg" <kellogg2@xxxxxxxxxxxx> wrote in message
news:1175321564.615781.227350@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Henri Wilson wrote:
[grammatical errors corrected to improve readability]
Hold a circle (or an ellipse) in front of you at any angle. Rotate your
head until you find an axis in the plane of the circle that is
horizontal to the line between your eyes, and is also perpendicular to
the LOS. (one always exists) ALL the radial velocities and the
accelerations around the orbit are then multiplied by the same factor,
cos(pitch), where the pitch angle refers to the rotation around the
above axis.
Rotating one's head is irrelevant. The rotation that you describe (A
"roll" of either the head or the projected ellipse) simply puts the long
axis of the projected ellipse on the viewer's X axis. That is
convienient but has no effect on the process of multiplying radial
velocities and accelerations around the orbit by a factor of cos(pitch).
You said this previously and I do not understand why George did not
point out its irrelevancy at that time.
Do I understand your terminology correctly as saying that the "pitch" of
an orbit is zero when seen edge-on and 90 degrees when seen face-on?
If so, your term "pitch" means the same as "inclination", which is the
term everyone else uses in astronomy. Though it is often measured as
angular deviation from face-on rather than from edge-on. That is how it
is used in arXiv astro-ph/0507420.pdf (Table 1, "Orbital inclination,
i")


To double-check that we are talking about the same thing, see the
illustration of "yaw", "pitch", and "roll" near the top of this page:
Leonard, I think Henry has just swapped some definitions for
convenience. His cos(pitch) is the same as the usual sin(inclination).
I'm less clear about his yaw but I'm fairly sure it is directly related
to the longitude of the ascending node.
George

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