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> 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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