# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Lunar distance accuracy
From: Frank Reed
Date: 2007 Oct 23, 21:39 -0400

```Alex, you wrote:
"These are all data I have. I will be very grateful if someone points to any
other hard data or research on the subject."

You may have missed the article by E.J. White from 1889 that I described on
the list almost a year ago --I know you get busy now and then and don't
follow the list as closely as you would like. Here's a paragraph from my
post back then:

"White then details the lunar distance observations he has made in the past
three years: forty-two lunars in 1887, 1888, and 1889. He lists the time and
measured distance (only approximately, not enough detail to re-work them
today) and also lists the error of the resulting longitude in seconds of
time. We can convert this to an approximate error in the measured lunar by
dividing by 120. That is, an error of 12 seconds in the longitude is
approximately equivalent to an error of 0.1 minutes of arc in the measured
lunar distance. Calculating from his listed numbers, I find he has a
standard deviation in Greenwich time of about 30 seconds which is equivalent
to about 0.25 minutes of arc in the lunar distances. If we take his lunars
in sets of four and average them (which I consider the best approach with
lunars), the results are generally within 0.1 minutes of arc. I would note
that these results are very similar to my own experience."

The original post is here:
http://fer3.com/arc/m2.aspx?y=200611&i=101759

As noted then, I found White's article originally while digging around in
Google Books. Since it's short, I've also made it available on the web here:
www.HistoricalAtlas.com/lunars/ejwhite.

-FER
www.HistoricalAtlas.com/lunars

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