NavList:

Triggered by Greg Rudzinki's "Turkey shoot challenge" I have been working on another way of working up M.P./ex-meridian positioning.
(based on the change of altitude close to transit according to "Bowditch")

Following through on this (which I have dubbed JotM's method for myself) I suspect the 4th reading here to be slightly off (I think it should have read 53°36.7') and I would have placed M.P. to have taken place at 00:49:27, putting the observer in Malibu, close to Paradise Cove Beach, not in Oxnard.

Jaap

[NavList] Daytime Jupiter Ex-Meridian/ M.P. /LOP Exercise
From: Greg Rudzinski
Date: 4 Jan 2011 19:02

5 Jan 2011 A.P. 34° 09.5'N 119° 13.5'W H.E. 21 ft. I.E. 0.0' Cassens Plath w/ 4x40mm scope

Declination 2° 17.8' S

UT 00:41:25 Hs 53° 32.4' (8m 26s to M.P.)
UT 00:44:39 Hs 53° 35.2' (5m 12s to M.P.)
UT 00:46:21 Hs 53° 36.2' (3m 30s to M.P.)
UT 00:47:59 Hs 53° 36.4' (1m 52s to M.P.)

UT 00:49:51 Hs 53° 36.8' M.P. observed

UT 00:51:37 Hs 53° 36.5' (1m 46s from M.P.)

Comments: The weather and horizon were excellent but it was a struggle to find and set Jupiter on the horizon. Jupiter would disappear against the sky and had to be lowered into the sea for viewing. The whole horizon mirror was just able to do the job. Next time it will be the split mirror. I have my doubts that this observation could be performed on a small craft. Aboard ship shouldn't be a problem. I did use Byron's vertical sextant technique of rocking the body from horizon to horizon through the dark back ground of the sea then splitting the difference to get the mid point.

Greg Rudzinski
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