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From: Mike Hannibal (no email)
Date: Mon Dec 05 2005 - 23:09:00 EST
Hi Bill,
glad you were encouraged, but much more intrepid than
me!
Thanks for your thoughtful comments today, I was
interested to see from your series that you too have a
tendency to get negative numbers. Though of course you
are much more accurate and consistent than I am.
My interpretation is that a negative number is an
indication that we have under measured the difference.
That therefore means that we are not bringing the two
bodies close enough together.
Thinking about this issue. I reckon that one of the
issues is that I was trying to bring the bodies into
contact, rather than trying to get the edge of the
moon to bisect Venus. This would then lead to an
underestimation of the distance.
The idea of some shades to balance the brightness is a
good one. Unfortunately a front went through this
morning and we have heavy overcast and rain at the
moment so no sights tonight.
Regards
Mike
--- Bill <> wrote:
> > This evening walking back from the supermarket I
> > noticed a fine opportunity for some lunars - the
> > crescent moon close to Venus...
>
> Mike
>
> You encouraged me to take advantage of Venus for
> some lunars. Downside, it
> was 11d F here in West Lafayette, IN. (N 40 27.7, W
> 86 55.7)
>
> Made 4 observations between 6:35 pm and 6:45:35 pm
> EST, Nov 5 (local date).
>
> I preset the first observation for a slightly
> exaggerated overlap (right
> side of Venus touching the moons right edge), popped
> out the door and then
> did a set-and-wait, noting the time when Venus
> appeared to be split. Then
> popped in and conformed the reading and recorded the
> time.
>
> I had precalculated an increase of approx. 0.4' per
> minute, so repeated the
> above 3 more times, did an IE check, and ran the
> results on Frank's site.
>
> Observation Error
> #1 -0.2'
> #2 -0.1'
> #3 -0.1'
> #4 -0.2'
>
> #1 and #2 with neutral-density shade over moon and
> light green over Venus:
> #3 and #4 with neutral-density and light-green shade
> over moon and light
> green over Venus.
>
> I was pretty pleased, but then the separation was
> only in the upper 15d
> range, so relatively easy. I was somewhat surprised
> all were under. Coming
> from overlap I would have thought I might have seen
> Venus split by the
> moon's rim a bit too soon, and have been slightly
> over.
>
> While doing the observations I remembered one other
> little "trick" I use,
> especially when measuring star-to-star separation.
> If you notice while
> doing IE checks with a faint star (when one image is
> still above/below the
> other) if you move the sextant slightly left or
> right, one will appear
> dimmer and the other brighter (with a split horizon
> mirror only). Moving
> the images a scosh right or left is nice way to
> "fine tune" the brightness
> relationship between two bodies.
>
> Good luck
>
> Bill
>
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