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From: Zorbec Legras (no email)
Date: Thu Sep 02 2004 - 04:58:47 EDT
----- Original Message -----
From: Bill <>
Date: Wed, 1 Sep 2004 14:51:44 -0500
To:
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.
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