# 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: Refraction and Artificial Horizons
From: Frank Reed CT
Date: 2006 May 23, 14:50 -0500

You don't need to apply a dip correction when you use an artificial
horizon, but in fact you do need to apply refraction.

For a specific case: suppose I measure the angle between a star and its
image reflected in a pan of mercury and find that it's 90 degrees
exactly. What's the true altitude? First, of course, I divide by two.
At 45 degrees altitude, the refraction is just about 1.0 minutes of
arc. Refraction always lifts the stars, so if I could remove the
atmosphere, the star is lower: 44d 59' in altitude. That's the altitude
I would use in celestial navigation calculations. If you measure the
same altitude from the sea horizon, you would find approximately 45d 4'
from an altitude of 16 feet, or 45d 5' from an altitude of 25 feet, and
so on (dip is nearly 1' * sqrt(ht in feet)).

-FER

--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To unsubscribe, send email to NavList-unsubscribe@fer3.com
-~----------~----~----~----~------~----~------~--~---

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)