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I just wrote-

"On the 29th April, the Sun's declination is increasing (Northward) by about
0.8 arc-minutes per hour. By a bit of rough guesswork, that's enough to
delay the moment of peak altitude, to be somewhere between 1 and 2 minutes
later than Meridian Passage. Which will throw out his assessments by that
amount."

However, that guesswork was a bit too rough. On second thoughts, I would
reassess that time offset, due to changing declination of the Sun, to be
about half a minute of time. Still well worth correcting for, however.

George.

contact George Huxtable, at  george@hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

========================
----- Original Message -----
From: "George Huxtable" 
To: 
Sent: Friday, September 25, 2009 9:23 PM
Subject: [NavList 9927] Re: Time of meridian passage accuracy


|
| Throughout his posting [9923], Douglas Denny appears to presume that
| Meridian Passage of the Sun occurs at the same moment as the maximum
| altitude of the Sun, at the peak of the curve of altitude with time.
|
| But it doesn't, except at the solstices, because of the Sun's changing
| declination. On the 29th April, the Sun's declination is increasing
| (Northward) by about 0.8 arc-minutes per hour. By a bit of rough
guesswork,
| that's enough to delay the moment of peak altitude, to be somewhere
between
| 1 and 2 minutes later than Meridian Passage. Which will throw out his
| assessments by that amount.
|
| To set up a precise North-South line, it's a factor that must be allowed
| for. For star observations, there's no such problem, as the declination
| stays constant.
|
| George.
|
| contact George Huxtable, at  george@hux.me.uk
| or at +44 1865 820222 (from UK, 01865 820222)
| or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
|
|
| |


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