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: A noon sight conundrum
From: Paul Hirose
Date: 2003 Dec 1, 15:02 -0800

```Kieran Kelly wrote:
>
> 3) In your learned opinion what was the time of meridian passage on that day
> at long 132d 40' E.

I'll use MICA 1.52 again, but this time working the problem with local
hour angle rather than azimuth as I did earlier.

MICA doesn't seem to have a way to display local hour angles, so I
have to get tabulations of sidereal time and the Sun's right
ascension, then subtract one from the other.

SIDEREAL TIME
Location:  E132?40'00", S21?48'18",     0m
(Longitude referred to Greenwich meridian)

Local App.
Date        Time      Sidereal Time
(UT1)
h  m   s    h  m   s
2002 Jul 20 03:15:38.0   7 57 14.4944
2002 Jul 20 03:15:39.0   7 57 15.4972
2002 Jul 20 03:15:40.0   7 57 16.4999

Sun
Apparent Topocentric Positions
True Equator and Equinox of Date
Location:  E132?40'00", S21?48'18",     0m
(Longitude referred to Greenwich meridian)

Date        Time      Right Ascension
(UT1)
h  m   s       h  m   s
2002 Jul 20 03:15:38.0      7 57 15.607
2002 Jul 20 03:15:39.0      7 57 15.610
2002 Jul 20 03:15:40.0      7 57 15.613

The differences:

UT1        LAST-RA
03:15:38   23:59:58.9
03:15:39   23:59:59.9
03:15:40   00:00:00.9

Meridian passage occurs .1 s after the middle time, i.e., at
03:15:39.1 UT1.

On that date UT1 was .23 s behind UTC, so the UTC time was
03:15:39.3.

As I said before, on this date MICA overestimates the TT-UT1
difference by 3.6 seconds. So the Sun's UT1 position against the fixed
stars is computed for a time 3.6 seconds later than the correct time.
In 3.6 s its right ascension increases .01 s, so strictly speaking all
the RA's I tabulated above should be decreased by .01 s to put them on
the UT1 time scale. That's too small to worry about.

```
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)