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From: Fred Hebard (no email)
Date: Sat Dec 20 2003 - 15:03:18 EST
Frank,
I reduced your data and plotted your lunar times against the time of
observation, below. The data look very nice; not as good as the lunar
of that Australian explorer Kieran Kelly discussed a few months ago,
but very good. The line is a least squares fit of a straight line.
Interestingly, I usually plot the raw distance against the time of
observation and use the least squares fit to pick out a point for
reduction. In this case, I chose your first observation, which was out
by 48 seconds. I should have chosen the third or fourth observation,
which, being in the middle, were closer to the fit of the line to the
average of the observations.
I think perhaps the old method of using the mean of the observations
would be better than using a line of best fit, although plotting the
data instantly tells one how good they are. Using the mean, the time
would have been out by 8 seconds, about 2 minutes of longitude.
Fred
Obs# time of observation time from lunar diff
1 12/19/03 9:30:37 12/19/03 9:31:24 48
2 12/19/03 9:33:31 12/19/03 9:34:28 58
3 12/19/03 9:36:15 12/19/03 9:35:50 -24
4 12/19/03 9:39:15 12/19/03 9:39:37 23
5 12/19/03 9:43:30 12/19/03 9:43:35 6
6 12/19/03 9:48:15 12/19/03 9:47:30 -45
7 12/19/03 9:52:30 12/19/03 9:52:22 -7
On Dec 20, 2003, at 3:53 AM, Frank Reed wrote:
> When you shoot lunars with Jupiter, you soon discover that the giant
> planet has a visible semidiameter through a good sextant. The accepted
> practice is to split the planet -- you take it to the Moon's limb and
> place the disk of the planet as best you can with its center right on
> the limb so that the planet is split in half along the Moon's limb.
> That's do-able...
>
> Fortunately, Jupiter is far enough away that parallax is no issue
> (it's always less than 0.04 minutes of arc for Jupiter).
>
> If anyone's interested, here's a set of Jupiter-Moon lunars from last
> night taken with a reliable Plath sextant:
>
> Index Correction: +0.7
> Assumed Position: Lat = 41d 22N, Lon = 71d 57W
> Temp: 30F. Pressure: Normal.
>
> All Lunars are Jupiter-Moon-Far Limb. Times are EST (US Eastern
> Standard Time). Sights start at Greenwich Date 12/19/2003, 09:30:
>
> 04:30:37, 43d 49.5
> 04:33:31, 43d 51.1
> 04:36:15, 43d 51.7
> 04:39:15, 43d 53.7
> 04:43:30, 43d 55.7
> 04:48:15, 43d 57.6
> 04:52:30, 44d 00.1
>
> Enjoy!
>
> Frank E. Reed
> [X] Mystic, Connecticut
> [ ] Chicago, Illinois
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