# 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: An interesting question
Date: 2013 Oct 10, 14:39 -0400

Why no artificial horizon.  You carried the sextant, almanac and sight reduction tables.  No AH?  odd.

On Oct 10, 2013 2:27 PM, "Lu Abel" <lu@abelhome.net> wrote:

```from a student in my celestial navigation class:

If one were on the Great Plains (of the US, for our non-US members)
could one take a sextant shot and get a LOP with reasonable accuracy?
The Great Plains are a vast area of what appears to be totally flat land.

My first instinct was (and still is) to say "no."   I don't believe the
human eye could distinguish a one degree slope in the ground, and so the
Great Plains easily could undulate.

But I also wondered if I were lost in my covered wagon with nothing but
a sextant and a Nautical Almanac, could I get a reasonable LOP?

I've driven from St Louis to Denver.  You cross vast areas of what
appears to be totally flat ground ("on a clear day you would be able to
see Pike's Peak except for the curvature of the earth" was a saying when
I was a student at the University of Illinois).

Let's assume it's truly flat ground.   Back of the envelope, the
distance is 1000 miles and the elevation gain is one mile.   That's a
right triangle with a hypotenuse of 1000 and an opposite side of 1.
Sine of a small angle is approximately equal to the angle itself
expressed in radians.   So the angle is 1/1000 radians or 3.5 minutes of
arc.

Assuming no undulation in the ground, getting a LOP that's off by 3.5

```

View and reply to this message: http://fer3.com/arc/m2.aspx?i=125279

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)