Fernando, Anthony and other Fellow Dialers I looked at the Celestaire page describing the Astro Compass and I envy Anthony that he has one. See for yourself http://www.celestaire.com/catalog/c_page35.html, it looks impressive. The new one is really expensive, nearly 300 bucks.
Imagine that when yesterday night I looked for the URL to the page describing compasses at Celestaire I could not resist the temptation and generated revenue again for this smart company by ordering the Vion Mini 2000 Compass. Besides marine sextant I bought from them small accessories like chamois, star finder and few other things. The compass should arrive in few days. Eh boys, will we ever grow up? Of other interesting stuff I have an old American sextant for aviators which I got from my friend who bought it for $25 at swap meet. The specimen I have is seriously damaged by time and abuse by previous owners. It has artificial horizon, incredibly complex optical system including 5 prisms and mechanical device for averaging sightings. Celestaire is still selling those and in spite of all the prisms and lenses they are below $1000 http://www.celestaire.com/catalog/c_page19.html Fernando sent me some remarks about practical use of compasses. General conclusion was that it is not that easy as it may seem after reading a book on orienteering or navigation. I may confirm this by my own yachting experience. Basic formulae are simple but you really better know them. And you need lots of practice too. I remember yachting trainees, University students at that, who after half an hour or so gave up and could not determine position by taking and plotting bearings to well visible lighthouses nearby. They forgot what corrections to apply and how, how to lay out angles on the chart, add to that sea sickness, sometimes a bit of fear, and here you are. And during lectures basic navigation was certainly simple, much simplier than University lectures on maths, physics or electrical engineering. Then they understood what navigation was really about, grit their teeth, set to work and all was fine after a time. My own way was just a little bit easier because I was well prepared for my first cruise (September or October in the Baltic) and grit my teeth from the very beginning. Another heartening conclusion is that this is not that hard that you cannot learn it. Slawek At 09:00 AM 2/9/99 -0500, Anthony wrote: >Celestaire also has, I believe, an Astro Compass which can locate compass >points accurately using the sun. Basically you set the device for the LHA >and Dec and rotate it until the sun casts a shadow between two locating >bars. The Astro Compass in the catalog is a bit pricey but I picked one up >used for very little. >Anthony > >> -----Original Message----- >> From: Slawomir K. Grzechnik [SMTP:[EMAIL PROTECTED] >> Sent: Tuesday, February 09, 1999 6:01 AM >> To: sundial@rrz.uni-koeln.de >> Subject: Re: Magnetic North >> >> Hello Fernando and other Fellow Dialers >> >> In spite of all the varieties of errors magnetic compasses were and still >> are very useful. Like Fernando I also used to possess more than one as I >> could not resist buying a nice thing for about $10. My offsprings worked >> hard however to bring that number down to two or three. >> >> Now in sports stores you may buy really good and robust compasses produced >> in Sweden and Finland. They are about $10, not very big but very accurate. >> The dial is marked every 2 degrees so with some skill, and when making a >> series of bearings, you may reach 1 degree accuracy. Do not hold such >> close >> to your eye but simply press its back side to your stomach while keeping >> the thing horizontally and try to take a bearing by turning yourself in >> the >> direction of your target. After few exercises you will gain confidence in >> this method. These compasses are filled with liquid which greatly >> stabilizes them and are guarranted to endure low pressure up to 5000 m >> above sea level, which is not always true. At least one of mine got >> bubbles >> in Yosemite at about 3000 m above sea level only (BTW, quite properly you >> reach this elevation driving your car as in America you should). These >> compasses are so cheap that it does not pay to send them back to producer >> if they break in spite of lifetime warranty. Their magnetic needle is so >> thin that it is physically nearly impossible to magnetize them otherwise >> than along the needle axis. >> >> When you buy a compass check first of all if the needle moves freely and >> if >> it stablilizes very fast. Then put the compass on any table inside the >> store, note the direction of the magnetic, rotate the compass few times >> and >> see if the needle comes back exactly to the same direction every time. >> >> Generaly good compass should be sensitive, stable and quiet, just like a >> good wife. >> >> A more expensive, excellent hand bearing compass you may order at >> >> http://www.celestaire.com/catalog/c_page34.html >> >> Other remarks. Yes, compass shows its own compass North, rather than >> magnetic North, let alone the true geographical North. Nearby objects made >> of steel bring in the compass error that deflects compass readings from >> magnetic readings. The only way to know this error is to measure it. In >> case of dialers this is no big deal as most of us know the geographical >> position and are cabable of calculating azimuths of celestial bodies at >> any >> given moment. Charts of magnetic variation are published, they also give >> variation changes with time so you may calculate variation for the given >> year. Even good touristic maps provide information on magnetic variation >> and its changes. After some practice all those things become natural. >> >> All best >> >> Slawek >> >> P.S. The Celestaire Company I gave the URL to, has quite a choice of >> marine >> and air navigation instruments and publications with prices generally >> lower >> than at marinas and coastal stores. The most funny thing is that the >> company is located in Kansas, right in the middle between the two Oceans. >> Their strategic planning was really flawless. About a year ago I bought a >> sextant from them and am really happy with it. >> >> At 10:34 PM 2/8/99 +0200, Fernando Cabral wrote: >> >Silas >> > >> >I did not know until recently, when I found I have more than 30 >> compasses: >> >I am a compass collector. Just for the fun of it, I started comparing >> different >> > >> >makers, models, styles. At first it came as a suprise to find that >> different >> >compasses will show completely different readings. 2, 3, 5 or even 10 >> degrees >> >east or west are quite common. >> > >> >Also, using the same compass you can get quite different readings as >> >a consequence of temperature (I guess), pressure (altitude) and, >> especially, >> >how you hold it in your hand. That is, if it is completely level or not, >> >inclined to one or the other direction, so on and so forth. >> > >> >Temperature and pressure will affect it especially if it has air bubles >> in >> >the liquid it is supposed to be suspended. I think the temperature will >> >also affect the way the needle pivots around it axle because of the >> friction. >> > >> >Also, I've found that sometimes, when you turn your compass 180 degrees, >> >it will not show 180 degrees but some degress more or some degrees less. >> > >> >The bottom-line is: there are too many factors influencing the reading. >> >As if that wasn't enough, a layperson can not use it properly, can >> >not even take parallax into acount, can not take into account local >> >forces like iron in the floor or in the wall. >> > >> >Here in Brazil we say that if counsels were good we would not give >> >them for free, we would charge for them. :-) but here my free advice >> >goes: don't ever ask your client to read a compass. 999 times in 1000 >> >they will give you completely wrong readings. In the 1 case left >> >reading will be within 2 or 3 degress off. >> > >> >- fernando >> > >> > >> > >> >-- >> >Fernando Cabral Padrao iX Sistemas Abertos >> >mailto:[EMAIL PROTECTED] http://www.pix.com.br >> > mailto:[EMAIL PROTECTED] >> >Fone: +55 61 321-2433 Fax: +55 61 225-3082 >> >15º 45' 04.9" S 47º 49' 58.6" W >> >19º 37' 57.0" S 45º 17' 13.6" W >> >> >> >> Slawek Grzechnik >> 32 57.4'N 117 08.8'W >> http://home.san.rr.com/slawek > Slawek Grzechnik 32 57.4'N 117 08.8'W http://home.san.rr.com/slawek
