NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Simplified Bris Sextant
From: �rjan Sandstr�m
Date: 2012 May 08, 18:52 +0200
From: �rjan Sandstr�m
Date: 2012 May 08, 18:52 +0200
It is a bit of a wait, but method is not much different than using precomputed altitudes in a more extreme manner than when normally shooting stars. I followed Sven's advice and fastened it to my sunglasses by clip (slaughtered a pair of cheap clip-on shades bought at petrol station), it gives a very stable image and I can do other things while waiting for sun image to approach horizon (like sitting on the ice fishing). I have mine calibrated for the four lowest suns, this far it has been within 1', not as good as my metal sextant but for something that can be carried inside a film can with plenty of room to spare it is impressive. I hope I give the information bellow correctly, this is from memory of something I read once over a decade ago (1997-1998 iirc), so likely I am not 100% correct on procedure this person used, and definitely out on vocabulary. I have had a link to a web-page that used a laser (the kind used by surveyors) and a theodolite to get the correct angles in a bris, he set this up inside a sports arena. If I remember it correctly it was important to take great care that both theodolite and bris shared the same "axle of rotation", the bris has no axle of rotation, but I guess it has some kind of "focal point"? The method required you to use sun semi diameter, dip, refraction... to get the correct angles but we are used to that :-) 2012-05-08 05:15, Alexandre E Eremenko skrev: > > Greg, > > I have to say that I do not find this Bris very practical. > It is rather a toy than a navigation device. > The reason is that you have to wait for these pre-assigned moments, > there are few of them during the day, and at these moments > Sun can be obscured by a cloud, or you can be busy with something > else, or just miss the moment. > > I am interested to hear from a list member who managed to > gratuate his/her Bris sextant:-) > > Alex. > > On Mon, 7 May 2012, Greg Rudzinski wrote: > >> >> Making a simplified Bris Sextant only requires gluing two microscope >> slides together with a gap at one end. The larger the gap the greater >> the angular deflection of the reflected Sun. I used a 0.7 mm pencil >> lead to set a gap and got 1* 57.8' of deflection. Inspect the linked >> image and you will see that the reflected image is the sum of four >> images one on top of the other. This must be from the front and back >> surface reflections from each slide. The best a navigator can >> probably hope for is 1' to 2' of precision on a home made version. >> Still this is pretty good for something that can get lost in a shirt >> pocket. >> >> Greg Rudzinski >> ---------------------------------------------------------------- >> NavList message boards and member settings: www.fer3.com/NavList >> Members may optionally receive posts by email. >> To cancel email delivery, send a message to NoMail[at]fer3.com >> ---------------------------------------------------------------- >> >>File:>> >> >> >> >> Attached File: http://fer3.com/arc/img/119461.f1-img_1189.jpg >> >> >> : http://fer3.com/arc/m2.aspx?i=119461 >> >> >> > > > >
