# 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: Beginner Meridian Passage Question
From: Zorbec Legras
Date: 2004 Sep 2, 03:58 -0500

----- Original Message -----
From: Bill
Date:         Wed, 1 Sep 2004 14:51:44 -0500
Subject:      Beginner Meridian Passage Question
============================

first things first

>> are there name [...] ?

1? for the line segment from the north horizon to the pole?
Call it lattitude.
zenith to elevated pole = colatitude
zenih to horizon = 90?
zenith - colatitude = latitude.

2? pole to zenith,
Colatitude (90?- latitude) see above

3? zenith to equator
Latitude

4? equator to southern horizon,
Colatitude.

5? Zenith to horizon
90? by definition

6? the unseen semicircle "through the nadir" ?
The "visible" apparent path of the sun is called "semi-diurnal arc",
So you can call the invisible path "invisible semi-diurnal arc".
The whole path is called "diurnal circle".
semi diurnal =>  arc cos P =  tan Lat * tan decl
A star is circumpolar if the colatitude is smaler than the declination.

(90? - Lat) < decl [same name] => circumpolar and visible.
(90? - Lat) < decl [diff name] => circumpolar and never visible.

Second...
>> When looking at times of meridian passage [...]

Upper transit occurs when LHA (AHg) is 0?
lower transit occurs when LHA is 180?

A circumpolar heav. body does have two transits, upper and lower.
You can know your latitude by observing the two transits of an unknown circumpolar star.
(true altitude upper transit + true altitude lower transit)/2 = latitude.

And the misconceptions...

>> -"I am guessing the same is true for the Southern Hemisphere"
Do not speak about southern or northern hemisphere.
The pole in the same hemisphere of the observer zenith is called : elevated pole.

>>"[...] twice in a sidereal or solar day."
mean solar day is 24h.
mean sideral day is 23h 56mn 4 sec.
It is not the same reference point.

--
___________________________________________________________
Sign-up for Ads Free at Mail.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)