A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2014 Jan 1, 13:53 -0500
From the pages provided Wright asserts
1) that the solstice altitudes of the sun were observed with a quadrant.
2) that the observations were recorded to 1/2 arc minute
3) that the solstice observations measured the maximum excursion of the declination of the sun. If I understand Alex correctly, then that declination excursion is good to 0.25 minutes of arc.
4) that he used Copernicus' mighty work as a reference, a mere 54 years after its publication (!!)
There are some points which must be deduced from the text
A) the quadrant uses the horizon for the reference. Other than specifying London, Wright does not tell us what body of water is used.
B) Wright does not tell us a dip table was used. We can assume that it was, because unless the HoE was 0, then the observation would have been in error by that amount.
C) Wright does not inform us as to whether the observation was ship or land based. There are problems with either one. If land based, then the TIDES affect the measurement, unless one can guarantee the same tide height for minima/maxima observations 6 months apart. If water based, the pendulum referenced as establishing vertical would be challenging at sea.
One additional point can be made. The assertion that a quadrant is only good to 10 arc minutes can be readily disposed of.
Gary, > I have also attached the June page showing Wright's > determination of the Sun's maximum declination as 23� 30' > north while the > modern value is 23� 26.3' a difference of only 3.7'. Did you take into account that obliquity of the ecliptic decreases at the rate about 0'.7 per century? More precisely, 46".8 per century. This implies that Wright wrote it correctly. I have not read the book yet:-) but I assume that he was using some astronomical tables available at that time, or did he determine all astronomical constants himself?? Alex. I have also included > Wright's explanation of how he determined the Sun's declination. > > http://en.wikipedia.org/wiki/Gregorian_calendar > > gl > > gl > > Attached File: http://fer3.com/arc/img/126089.march declination table from > wrights book.jpg > > Attached File: http://fer3.com/arc/img/126089.june declination from > wrights book.jpg > > Attached File: http://fer3.com/arc/img/126089.explanation of declination > determine by wright_page_1.jpg > > Attached File: http://fer3.com/arc/img/126089.explanation of declination > determine by wright_page_2.jpg > > > View and reply to this message: http://fer3.com/arc/m2.aspx?i=126089 > > > >
View and reply to this message: http://fer3.com/arc/m2.aspx?i=126097