# 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: Precomputed lunar distances
From: Frank Reed
Date: 2005 Apr 19, 19:44 EDT
Bill you wrote:
"In fact that is not what raised a red flag for me.  I had drilled down too
far and done a scatter graph with Excel, so every or hundredth or thousandth
was magnified."

Yeah, I wondered if that was part of the problem. Remember, if your input data is accurate to the nearest tenth of a minute of arc, generally you should quote your output data to the nearest tenth as well. Anything beyond that is just random garbage.

And:
"Now that you mention it, I recall a discussion about bodies
of equal observed altitude and the 0.6' minute figure."

Only around 37 degrees separation. Try out those equations from my last post. When the altitudes are exactly the same, the refraction correction to the distance in minutes of arc is
1.9*(1-cos(D))/sin(D).
You wrote:
"I apologize to the you and the list for rehashing a subject that was
apparently covered in October."

You take that back! :-)  There is absolutely nothing wrong with discussing the same topic after a few months off.

And:
"Regarding my question, "Another hypothetical scenario.  If I take the same
two stars, calculate true separation of 34d 27.7', they have identical Hc's
of 1d 36.8', and  hypothetical refraction is -88d, what separation might I
expect to measure with a sextant?"

I didn't respond to this before because I cannot for the life of me figure out what you're getting at. If you have two stars with an unrefracted distance of 34 deg 27.7' and you observe them down at 1.5 degrees altitude, then the measured distance will be very close to 34d 27.7'. What's this "-88d" number?

-FER
http://www.HistoricalAtlas.com/lunars
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)