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Re: Lunars: Jupiter's BIG.
From: Fred Hebard
Date: 2003 Dec 20, 15:03 -0500

```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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