NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: "Latitude"questions
From: Brooke Clarke
Date: 2003 Sep 26, 17:26 -0700
From: Brooke Clarke
Date: 2003 Sep 26, 17:26 -0700
Hi Doug:
Here is the idea:
http://americanhistory2.si.edu/surveying/object.cfm?recordnumber=758935
The passage you quoted was:
" . . observer would then reverse the scope 180* on the verticle plane . . "
Where today we would say "in the verticle plane", not axis.
Have Fun,
Brooke
Royer, Doug wrote:
Here is the idea:
http://americanhistory2.si.edu/surveying/object.cfm?recordnumber=758935
The passage you quoted was:
" . . observer would then reverse the scope 180* on the verticle plane . . "
Where today we would say "in the verticle plane", not axis.
Have Fun,
Brooke
Royer, Doug wrote:
Thanks for the replies on this matter Brooke and Mitch.I now understand what 1900 has to do with 1896 and can see what was being conveyed. After reading your reply of the "Meridian Scope" I did a search to find pictures or details of one but came up dry.I still can not visualise what it looks like and how one would rotate it 180* on its verticle axis and still be able to view the star with the objective lens in the proper place. -----Original Message----- From: Brooke Clarke [mailto:brooke@pacific.net] Sent: Friday, September 26, 2003 14:18 To: Navigation Mailing List; doug.royer@REMEC.COM Subject: Re: "Latitude"questions Hi Doug: I don't have the book so can only give my opinion. A "meridian scope" is one that only has a single axis of rotation aligned East - West and is always looking in the North - South plane containing the local longitude. This is the type of scope at Greenwich at 0 degrees longitude. You just set the elevation of the scope to match that declination of a star and make a hack when it crosses one of the reticule lines. If it takes a star, say 1 minute of time to cross each reticule line, then the scope could be inverted between each time hack. Treating the even and odd hack marks as two different time series would allow some scope alignment errors to be corrected. The Photographic Zenith Telescope (PZT) was used for many decades to set the master clocks of the USNO and other time standard locations. It has a more complicated way to eliminate errors. Most, but not all, stars are in a fixed location on the celestial sphere. But the Earth precesses just like a gyroscope and also wobbles. This causes the apparent position of a star to change, so to accurately point to a star you need to know where it was on a given epoch date and how much the Earth has precessed and wobbled since then. Have Fun, Brooke Clarke, N6GCE http://www.pacificsites.com/~brooke/Nav.shtml Royer, Doug wrote:I am reading my copy of the book "Latitude" and have some questions on 2 subjects I ran across. On pages 61 thru 64 a method for the "telegraphing of correcting longitude" useing a telegram is explained.All well and good.For those who don't have the book here is a short explaination of the method.Each station used to relay the time was equiped with a chrono,telegraph key,telescope that would rotate 180* on it's verticle axis and a cylendrical record.At every 2 sec. of time the chrono would cause a tick to be recorded on the record as would every minute be recorded as a double tick.The observer would then use the special telescope and observe a celestial body's movement in thereticle.Asthe body crossed a series of lines in the reticle the observer woulddepressa telegraph key which would also record a tick on the record.Then the observer would then reverse the scope 180* on the verticle plane and repeat the proceedure to cancel certain errors and allow corrections to becomputedfor others.I cannot visualize this scope.Can anyone help? On pages 84 and 85 it states that in 1896 the rules governing the nomemclature of variable stars were inconsistant at the time.The locations of the stars were expressed by R.A. and Declination.All well and good so far.Here's where I get lost:"in Seth Chandler's system the designation of a variable star was obtained by dividing by ten the number of secounds in its R.A. during the year 1900". As like Forrest Gump I can say "I am not a smart man" but this statementhasme totally baffled! Can someone in the list please explain what is being conveyed as I don't understand what 1900 has in common with 1896. Thanks for any insights you can give me.