NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Aligning a transit telescope to the meridian
From: Greg R_
Date: 2008 Apr 21, 16:49 -0700
From: Greg R_
Date: 2008 Apr 21, 16:49 -0700
> First would be use Polaris, of course. But given that a transit > telescope looks South, it may be inconvenient to use Polaris - > especially at these high latitudes (Scotland) I'm not sure how a transit telescope is aligned in the real world, but how about using Polaris to establish a true north/south line (with the appropriate corrections from an almanac, etc.), then using something like a surveyor's rod setup on the south side of that line to setup the 'scope facing true south? Sounds like an intuitive solution to me, at least... -- GregR --- Geoffrey Kolbewrote: > > With the recent discussion on the abolition of the leap-second and > the > problems of Delta T, I have been pondering the possibility of > measuring > Delta T myself. > > The transit telescope was invented by that Danish polymath genius Ole > > Roemer in about 1675 and quickly adopted by Greenwich and then by all > the > world's observatories as a means to determine time. So, this seems a > good > way to go. But the main problem would be setting the telescope up so > that > it was aligned to the meridian. With a transit theodolite - which is > essentially a portable alt-az telescope - one can easily time the > moment a > star or the sun transits the vertical cross wire in the telescope. > Using > the calculated azimuth of the sun or star for that moment, it is easy > to > correct the plate azimuth of the theodolite and swing it around to > the > meridian. But, since I want to use the telescope to measure time, I > would > prefer to find some other way to set it up which did not involve the > use of > absolute time. > > It seems that in England, there was a flurry of interest in small > transit > telescopes in the late 19th century as country gentlemen and the > newly rich > industrialists needed some way to determine the time in their country > > estates. To this end, a book called "A Treatise on the Transit > Instrument > as Applied to the Determination of Time" was written in 1882 by > Latimer > Clark. Unfortunately, although Google books tantalizingly lists the > contents of the book, it does not seem to be available. > > There are a couple of ways that I can think of. First would be use > Polaris, > of course. But given that a transit telescope looks South, it may be > inconvenient to use Polaris - especially at these high latitudes > (Scotland). Second would be to time the transits of two stars of > preferably > similar SHA but greatly differing declination. Only if the telescope > is > aligned to the meridian will the difference in transit times be > correct. > > Can anyone come up with any other ways to align a transit telescope > to the > meridian, which does not involve the use of absolute time? > > Geoffrey Kolbe > > > > > > > > > > > --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---