# 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:
Dip: Astronomical Almanac vs. Nautical Almanac
From: Marcel Tschudin
Date: 2013 Apr 22, 00:48 +0300

```While searching in the Internet something completely different I dropt
on an excerpt of the "Explanatory Supplement to the Astronomical
Almanac" containing "9.331 The Effects of Dip and Refraction". Reading
its content here

I notice that dip appears to differ to how I understand it is used in
the Nautical Almanac.

Nautical Almanac
----------------
It mentions calculating the dip consisting (to my understanding) of
the geometrical angle and *including* the effects of terrestrial
refraction as
DIP[moa]=1.76*sqrt(H[m])

Astronomical Almanac
--------------------
Here almost the same equation as in the Nautical Almanac is mentioned
but for what appears to calculate only the geometrical dip:
DIPgeom[moa]=1.75*sqrt(H[m])
The terrestrial refraction appears then to be considered seperately by
REFdip[moa]=0.37*sqrt(H[m])
to the geometrical part and resulting in what appears to be the total
(or apparent) value
DIP[moa]=2.12*sqrt(H[m]) = DIPgeom + REFdip

Where could the misunderstanding be for

1) Almost the identical factor for calculating dip with and without
terrestrial refraction? Do the two Almanac treat the dip indeed so
much different?

2) The terrestrial refraction being added whereas to my understanding
it reduces the geometrical dip and should therefore be subtracted?

Any ideas?

Marcel
```
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)