# NavList:

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

Message:αβγ
Message:abc
 Add Images & Files Posting Code: Name: Email:
Re: Lunars: how to use the prop.log tables?
From: Tony Oz
Date: 2016 Sep 1, 09:23 -0700

Thanks, Robin.

Here’s a modified segment of the explanation at http://fer3.com/arc/m2.aspx/Lunars-how-use-proplog-tables-EdPopko-aug-2016-g36381

-------------------------------------------------------------------------------------------

12:00 UT, 84° 35'.2, PL 2620

pLogD =   2620

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 = 2766

Thus ...

--------------------------------------------------------------------------------------------------

The difference between 2623 calculated directly and 2620 from the Almanac propagates through and changes the final result slightly

I'm sure Ed was right about the value of plog D.

D is NOT from the Almanac, it should be calculated as a "width" between the tabulated brackets:

84° 35.2' - 82° 56.8' = 1° 38.4'

because D is the whole change of the lunar distance (that will happen during the full 3 hours between the brackets) from which we need to find a part corresponding to the actual change that happened since the first tabulated bracket.

So plog D = plog(1° 38.4') = 2623.

Further is just my nitpicking: because the resulting plog t = 143 is two-thirds closer to the tabulated value of 142 than to 145 I must interpolate the time t two-thirds closer to 02:54:12 from 02:54:06, and rather than picking the middle of the interval (i.e. 02:54:09) I must take it as 02:54:10.

The final value of UTC of the lunar must be 14:54:10.

Regards,

Tony

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)