Chronology Current Month Current Thread Current Date [Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

# Re: [Phys-L] Trick photography?

There is one other subtle effect related to the inclination of the Moon's orbit to the Earth's equatorial plane. Because that inclination is only 5 degrees it doesn't produce very noticeable changes in the apparent rate of motion. But imagine that the inclination were, say, 80 degrees. In that case the apparent motion of the moon would depend strongly on the orbital phase. Twice a month the moon would be found only 10 degrees away from a celestial pole and at those times its apparent motion would be very small.

John Mallinckrodt
Cal Poly Pomona

On Mar 3, 2014, at 8:23 AM, Bob Sciamanda wrote:

I'm still learning (a good sign)! ==>
I am just realizing that the apparent moon speed is NOT calculable as the
moon's linear orbital speed minus the linear spin speed of an earth surface
point.

IE., Vap is NOT= {(6.28*250000)/(30*24) - (6.28*4000)/24} miles/hr. This is
grossly wrong - even in direction!

Instead, Vap = {6.28/(30*24)-6.28/24}*250000 miles/hr. => the relative
ANGULAR velocity times the moon's orbital radius.

It is incorrect to treat the earth observer as viewing a linear motion from
a linear moving frame. We must acknowledge that the earth observer is
viewing a rotational motion from a rotational frame. Note that this turns
the moon's actual EASTWARD motion into the observed WESTWARD motion. The
linear mistreatment fails to even do this.

Again, thanks to John M for leading me to this realization.

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
treborsci@verizon.net
http://sciamanda.com

_______________________________________________
Forum for Physics Educators
Phys-l@phys-l.org
http://www.phys-l.org/mailman/listinfo/phys-l