# NavList:

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

### Compose Your Message

Message:αβγ
Message:abc
 Add Images & Files Posting Code: Name: Email:
Re: Lunars: how to use the prop.log tables?
From: Ed Popko
Date: 2016 Aug 30, 15:05 -0700

Tony,

I'm unskilled at explaining math sequences but I'll give it a try. If you search the NavList archives you will find some very good discussions about why prop logs came to be and how tables were created. Jeff Gottfred's "Lunar tables - use of prop logs" is a very good post.  See: http://fer3.com/arc/m2.aspx/Lunar-tables-use-prop-logs-Gottfred-jan-1995-w804   for a complete explanation.

So it boils down to this ..

pLogt = pLogd - pLogD

Where ...

D is total change in LD distance from first time (12:00) to last time (15:00) in bracket. Three hours or 60x60x3=10800 seconds.

Using your post data ...

D = 84° 35.2' - 82° 56.8'
= 1° 38.4'

Looking 1° 38.4' up in table ...
pLogD =   2766

and ...

d is total change in LD distance from First time (12:00) to your unknown time of lunar sight
d = 84° 35.2' - 83° 00.0'
= 1 35.2'
Looking 1 35.2' up in table ...
pLogd = 2623

Thus ...

The pLogt is their difference
pLogt = 2766 - 2623
= 143

Looking up 143 in table falls between tabulated 142 and 145,  so I guess it is about 02:54:09

Add this offset (time of your lunar from first time bracket)

12:00:00
+ 02:54:09
-----------
Time of lunar  12:54:09

Ed Popko

Browse Files

Drop Files

### Join NavList

 Name: (please, no nicknames or handles) Email:
 Do you want to receive all group messages by email? Yes No
You can also join by posting. Your first on-topic post automatically makes you a member.

### Posting Code

Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
 Email:

### Email Settings

 Posting Code:

### Custom Index

 Subject: Author: Start date: (yyyymm dd) End date: (yyyymm dd)