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celestrial navigation anyone?
Can you navigate (lat and long) at night with a sextant and a compass, but
without a nautical almanac, sight reduction tables, the time of day, and without knowing the names of the stars? The sextant has an error, but you don't know what it is, just that it's off. You can keep your modern watch, but you just replaced the battery and the time is wrong. Does someone own a sextant? What model? I'm thinking about picking one up. -- "j" ganz @@ www.sailnow.com |
celestrial (celestrial? How about celestial?) navigation anyone?
IDIOT!!!
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celestrial navigation anyone?
Dutton wrote in message ...
On Sun, 20 Apr 2008 11:26:00 -0700, "Capt. JG" wrote: Can you navigate (lat and long) at night with a sextant and a compass, but without a nautical almanac, sight reduction tables, the time of day, and without knowing the names of the stars? The sextant has an error, but you don't know what it is, just that it's off. You can keep your modern watch, but you just replaced the battery and the time is wrong. Are you talking about finding one location with one measurement or by taking several measurements over a period of time? What degree of error is acceptable? What a screwball question - do you even understand what you are asking? Get a cheap one, you probably will never master it as an instrument and never understand the mathematics behind it. http://www.jbs.org/node/163 Dutton You're another sockpuppet asshole, given the link you posted.... nothing to say, with a lot of time on your hands. You're quite pathetic. Keep changing identities if it makes you feel more like a man. -- "j" ganz @@ www.sailnow.com |
celestrial navigation anyone?
On Sun, 20 Apr 2008 11:26:00 -0700, "Capt. JG"
wrote: Can you navigate (lat and long) at night with a sextant and a compass, but without a nautical almanac, sight reduction tables, the time of day, and without knowing the names of the stars? The sextant has an error, but you don't know what it is, just that it's off. You can keep your modern watch, but you just replaced the battery and the time is wrong. I assume this is a quiz? You can use a sextant to measure horizontal angles and take relative shore bearings, other than that I think you're out of luck. You can not take star sights at night (no horizon), only at twilight. Does someone own a sextant? What model? I'm thinking about picking one up. I've owned this one for years and people have crossed oceans with it: http://tinyurl.com/6fdkfr It works but I prefer my GPS chartplotter. |
celestrial navigation anyone?
On Sun, 20 Apr 2008 13:12:44 -0600, Dutton wrote:
Get a cheap one, you probably will never master it as an instrument and never understand the mathematics behind it. http://www.jbs.org/node/163 Dutton Dutton relied on Bowditch. |
celestrial navigation anyone?
"Capt. JG" wrote: Does someone own a sextant? What model? I'm thinking about picking one up. I still have a new Davis MK 15 for sale. Lew |
celestrial navigation anyone?
"Wayne.B" wrote in message
... On Sun, 20 Apr 2008 11:26:00 -0700, "Capt. JG" wrote: Can you navigate (lat and long) at night with a sextant and a compass, but without a nautical almanac, sight reduction tables, the time of day, and without knowing the names of the stars? The sextant has an error, but you don't know what it is, just that it's off. You can keep your modern watch, but you just replaced the battery and the time is wrong. I assume this is a quiz? You can use a sextant to measure horizontal angles and take relative shore bearings, other than that I think you're out of luck. You can not take star sights at night (no horizon), only at twilight. Does someone own a sextant? What model? I'm thinking about picking one up. I've owned this one for years and people have crossed oceans with it: http://tinyurl.com/6fdkfr It works but I prefer my GPS chartplotter. Yes, it's a quiz and it's possible... Not sure what you mean about not being able to use it at night... What about the artificial horizon common on modern sextants? http://en.wikipedia.org/wiki/Sextant I'm somewhat familiar with the Davis models... thinking about playing around with the 25. -- "j" ganz @@ www.sailnow.com |
celestrial navigation anyone?
"Lew Hodgett" wrote in message
news:z3NOj.3364$aq4.2434@trnddc02... "Capt. JG" wrote: Does someone own a sextant? What model? I'm thinking about picking one up. I still have a new Davis MK 15 for sale. Lew Hey Lew... haven't forgot... I think I'm going to get one as a gift, so.... -- "j" ganz @@ www.sailnow.com |
celestrial navigation anyone?
"Capt. JG" wrote: Hey Lew... haven't forgot... I think I'm going to get one as a gift, so.... Send the 'giver' my way. Everybody makes out. Lew |
celestrial navigation anyone?
"Capt. JG" wrote in message news:J8ednTRMl5onF5bVnZ2dnUVZ_gqdnZ2d@bayareasolut ions... Can you navigate (lat and long) at night with a sextant and a compass, but without a nautical almanac, sight reduction tables, the time of day, and without knowing the names of the stars? The sextant has an error, but you don't know what it is, just that it's off. You can keep your modern watch, but you just replaced the battery and the time is wrong. I say that you cannot. Firstly because at night you probably cannot see exactly where the horizon is.Even if you got an aeronautical sextant with a bubble level they are very hard to read on a boat if it is at all rough Secondly because you cannot derive longitude without an accurate watch. Does someone own a sextant? What model? I'm thinking about picking one up. You do not say what you want it for. For use aboard or just as a talking point at home?. You can get various plastic sextants that do a good enough job for use on a small boat where pinpoint accuracy is hard to achieve. But a proper sextant is a thing of beauty and mine is a Kelvin Hughes dating from 1959 which is in pristine condition in its box with all accessories. I take the odd reading with it from time to time to keep my hand in in case both my chartplotter and my DR on paper charts fail me. Mine is a micrometer type but retains the silver engraved scale which is somewhat overkill for a micrometer since you only need to use the scale to read whole degrees. But it is very nice to look at an inlaid silver scale. Vernier sextants are older and are collectable antiques now and regrettably mostly end up in museums or hanging on someone's wall. There are a lot of authentic looking but purely decorative ones about which are not suitable for navigation. Make sure yours comes with an authentic test certificate. |
celestrial navigation anyone?
On Sun, 20 Apr 2008 12:51:53 -0700, "Capt. JG"
wrote: Not sure what you mean about not being able to use it at night... What about the artificial horizon common on modern sextants? It might be possible but I doubt it. There used to be a sextant designed for aircraft navigation in WW II that used an artificial horizon of sorts but those guys were happy to know where they were within 20 miles or so. You can get latitude without accurate time by taking a series of noon sites and plotting the maximum elevation. Longitude to any reasonable degree of accuracy is very difficult without accurate time. |
celestrial navigation anyone?
"Wayne.B" wrote in message
... On Sun, 20 Apr 2008 12:51:53 -0700, "Capt. JG" wrote: Not sure what you mean about not being able to use it at night... What about the artificial horizon common on modern sextants? It might be possible but I doubt it. There used to be a sextant designed for aircraft navigation in WW II that used an artificial horizon of sorts but those guys were happy to know where they were within 20 miles or so. You can get latitude without accurate time by taking a series of noon sites and plotting the maximum elevation. Longitude to any reasonable degree of accuracy is very difficult without accurate time. Not only possible, but people take star sightings all the time. Besides the Sun, how many stars are you expecting to see during the day? Yes, you can get an LOP with the information/equipment I supplied. I didn't make this up, wish I did, but it works. -- "j" ganz @@ www.sailnow.com |
celestrial navigation anyone?
"Edgar" wrote in message
... "Capt. JG" wrote in message news:J8ednTRMl5onF5bVnZ2dnUVZ_gqdnZ2d@bayareasolut ions... Can you navigate (lat and long) at night with a sextant and a compass, but without a nautical almanac, sight reduction tables, the time of day, and without knowing the names of the stars? The sextant has an error, but you don't know what it is, just that it's off. You can keep your modern watch, but you just replaced the battery and the time is wrong. I say that you cannot. Firstly because at night you probably cannot see exactly where the horizon is.Even if you got an aeronautical sextant with a bubble level they are very hard to read on a boat if it is at all rough Secondly because you cannot derive longitude without an accurate watch. Does someone own a sextant? What model? I'm thinking about picking one up. You do not say what you want it for. For use aboard or just as a talking point at home?. You can get various plastic sextants that do a good enough job for use on a small boat where pinpoint accuracy is hard to achieve. But a proper sextant is a thing of beauty and mine is a Kelvin Hughes dating from 1959 which is in pristine condition in its box with all accessories. I take the odd reading with it from time to time to keep my hand in in case both my chartplotter and my DR on paper charts fail me. Mine is a micrometer type but retains the silver engraved scale which is somewhat overkill for a micrometer since you only need to use the scale to read whole degrees. But it is very nice to look at an inlaid silver scale. Vernier sextants are older and are collectable antiques now and regrettably mostly end up in museums or hanging on someone's wall. There are a lot of authentic looking but purely decorative ones about which are not suitable for navigation. Make sure yours comes with an authentic test certificate. I never said it would necessarily be a boat that was in rough conditions. That is always difficult. The sextant would be a backup, a talking point, and something to mess with. -- "j" ganz @@ www.sailnow.com |
celestrial navigation anyone?
Dutton wrote:
On Sun, 20 Apr 2008 11:26:00 -0700, "Capt. JG" wrote: Can you navigate (lat and long) at night with a sextant and a compass, but without a nautical almanac, sight reduction tables, the time of day, and without knowing the names of the stars? The sextant has an error, but you don't know what it is, just that it's off. You can keep your modern watch, but you just replaced the battery and the time is wrong. Why do you need all that stuff? The south pacific islander types followed the appropriate star in the appropriate constellation and got along just fine! Gordon |
celestrial navigation anyone?
"Wayne.B" wrote in message ... It might be possible but I doubt it. There used to be a sextant designed for aircraft navigation in WW II that used an artificial horizon of sorts but those guys were happy to know where they were within 20 miles or so. That was not a sextant. It was called an octant. Here's one: http://www.icarusbooks.com/images/1458.jpg |
celestrial navigation anyone?
On Sun, 20 Apr 2008 16:22:29 -0700, "Capt. JG"
wrote: Yes, you can get an LOP with the information/equipment I supplied. I didn't make this up, wish I did, but it works. Well please enlighten us. Heavenly bodies still hold a certain appeal in these days of push button navigation. |
celestrial navigation anyone?
"Wayne.B" wrote in message
... On Sun, 20 Apr 2008 16:22:29 -0700, "Capt. JG" wrote: Yes, you can get an LOP with the information/equipment I supplied. I didn't make this up, wish I did, but it works. Well please enlighten us. Heavenly bodies still hold a certain appeal in these days of push button navigation. They do for me as well, although I'm not familiar with more than the basics. I'd be happy to, but just to be clear, I didn't come up with this, and I haven't tried it. It seems to be logically correct, and I'd like to try. If you have a sextant, and you want to try it, I'd love to hear the result. When I get one, I'm definitely going to give it a try. Courtesy of a Celestaire handout at a seminar I attended. No mention was made of accuracy, which I would think is dependent upon the adjustment of the various instruments (sextant, compass, watch), as well as the observer. Most of you are familiar with the stroboscopic effect. That's why the flashing light makes the dancers seem to be frozen, or at least to have jerky movements. We check the timing of motors with a flashing strobe, which makes the rotating timing marks seem to stand still. You can do the same thing with the stars. Stars move through the sky so regularly that every 23 hours 56 minutes and 4 seconds, each star is back in the same place as the night before. This means that if you laid on the ground facing up, and every 23h 56m 4s you opened your eyes for a moment, the stars would appear to be stationary in space, always in the same place. If you took a round of sextant readings on any of the stars you cared to keep track of (you can give them any names you wish), the readings would be the same night after night, as long as you did it every 23h 56m 4s instead of every 24 hours. The readings would remain the same - unless you moved! If you move between the readings, your movement will be reflected in changed readings - one minute of arc for every mile you moved. If a star's reading increases by 23' for example, then you must have moved 23 miles in its direction. If you have a compass with you when taking readings, you will know what direction to plot the new line of position. You simply plot a line from your previous position in the direction of the star, measure 23 miles (the intercept) and plot a line perpendicular at this point. This is your new LOP. If you do the same for several other stars, you have a new fix. The advantage of this method is that it is incredibly easy to do. You don't even have to correct for refraction or dip. Even if your sextant has an error, it won't matter. The disadvantage is that each position depends upon the previous one, so that small errors may build up to be large ones. If you are on a long voyage, you may find that the original stars are no longer visible at a time when they are useful. Before this happens, you will need to pick some new stars, and take a double round of sights - one for the fix, and one to establish a basis with the new stars. -- "j" ganz @@ www.sailnow.com |
celestrial navigation anyone?
On Sun, 20 Apr 2008 18:08:02 -0700, Gordon wrote:
Why do you need all that stuff? The south pacific islander types followed the appropriate star in the appropriate constellation and got along just fine! Gordon Did they? Maybe we just don't know how many of them got lost. ;-) |
celestrial navigation anyone?
Capt. JG wrote:
"Edgar" wrote in message ... "Capt. JG" wrote in message news:J8ednTRMl5onF5bVnZ2dnUVZ_gqdnZ2d@bayareasolut ions... Can you navigate (lat and long) at night with a sextant and a compass, but without a nautical almanac, sight reduction tables, the time of day, and without knowing the names of the stars? The sextant has an error, but you don't know what it is, just that it's off. You can keep your modern watch, but you just replaced the battery and the time is wrong. I say that you cannot. Firstly because at night you probably cannot see exactly where the horizon is.Even if you got an aeronautical sextant with a bubble level they are very hard to read on a boat if it is at all rough Secondly because you cannot derive longitude without an accurate watch. Does someone own a sextant? What model? I'm thinking about picking one up. You do not say what you want it for. For use aboard or just as a talking point at home?. You can get various plastic sextants that do a good enough job for use on a small boat where pinpoint accuracy is hard to achieve. But a proper sextant is a thing of beauty and mine is a Kelvin Hughes dating from 1959 which is in pristine condition in its box with all accessories. I take the odd reading with it from time to time to keep my hand in in case both my chartplotter and my DR on paper charts fail me. Mine is a micrometer type but retains the silver engraved scale which is somewhat overkill for a micrometer since you only need to use the scale to read whole degrees. But it is very nice to look at an inlaid silver scale. Vernier sextants are older and are collectable antiques now and regrettably mostly end up in museums or hanging on someone's wall. There are a lot of authentic looking but purely decorative ones about which are not suitable for navigation. Make sure yours comes with an authentic test certificate. I never said it would necessarily be a boat that was in rough conditions. That is always difficult. The sextant would be a backup, a talking point, and something to mess with. They look great on the mantleshelf. A wow at cocktail parties. Buy plenty of Brasso. Dennis. |
celestrial navigation anyone?
ask wilbur
"Capt. JG" wrote in message news:J8ednTRMl5onF5bVnZ2dnUVZ_gqdnZ2d@bayareasolut ions... Can you navigate (lat and long) at night with a sextant and a compass, but without a nautical almanac, sight reduction tables, the time of day, and without knowing the names of the stars? The sextant has an error, but you don't know what it is, just that it's off. You can keep your modern watch, but you just replaced the battery and the time is wrong. Does someone own a sextant? What model? I'm thinking about picking one up. -- "j" ganz @@ www.sailnow.com |
celestrial navigation anyone?
On Sun, 20 Apr 2008 18:08:02 -0700, Gordon wrote:
Dutton wrote: On Sun, 20 Apr 2008 11:26:00 -0700, "Capt. JG" wrote: Can you navigate (lat and long) at night with a sextant and a compass, but without a nautical almanac, sight reduction tables, the time of day, and without knowing the names of the stars? The sextant has an error, but you don't know what it is, just that it's off. You can keep your modern watch, but you just replaced the battery and the time is wrong. Why do you need all that stuff? The south pacific islander types followed the appropriate star in the appropriate constellation and got along just fine! Gordon Well, possible. Of course those times it didn't quite work we didn't hear about it... Bruce-in-Bangkok (correct email address for reply) |
celestrial navigation anyone?
On Sun, 20 Apr 2008 20:25:09 -0600, "Roger Helio"
wrote: "Wayne.B" wrote in message .. . It might be possible but I doubt it. There used to be a sextant designed for aircraft navigation in WW II that used an artificial horizon of sorts but those guys were happy to know where they were within 20 miles or so. That was not a sextant. It was called an octant. Here's one: http://www.icarusbooks.com/images/1458.jpg I've got no idea what that thing you referenced is but I can assure you that the devices carried aboard aircraft, at least until the 1970's was called a "Bubble Sextant" and didn't look a thing like your picture. Bruce-in-Bangkok (correct email address for reply) |
celestrial navigation anyone?
On Sun, 20 Apr 2008 22:57:42 -0700, "Capt. JG"
wrote: The advantage of this method is that it is incredibly easy to do. You don't even have to correct for refraction or dip. Even if your sextant has an error, it won't matter. Conceptually it works but has big issues in real life. As mentioned previously accurate star sights are only available for a few minutes at sunrise and sunset every day. The times of sunrise and sunset are changing every day from both seasonal variation and also from your own travel. And of course there are many days when no sights are possible because of overcast weather. |
celestrial navigation anyone?
On Mon, 21 Apr 2008 18:55:22 +0700, Bruce in Bangkok
wrote: That was not a sextant. It was called an octant. Here's one: http://www.icarusbooks.com/images/1458.jpg I've got no idea what that thing you referenced is but I can assure you that the devices carried aboard aircraft, at least until the 1970's was called a "Bubble Sextant" and didn't look a thing like your picture. Yes. http://www.warbirdsite.com/museumnavigation.html http://www.nautical-products.com/bubble-sextants.html http://www.physics.uq.edu.au/physics...ant_manual.pdf http://www.qmss.com/seastories/seastory05.html |
celestrial navigation anyone?
Capt. JG wrote:
.... The disadvantage is that each position depends upon the previous one, so that small errors may build up to be large ones. No, you can go a number of days referencing the last fix. If you are on a long voyage, you may find that the original stars are no longer visible at a time when they are useful. Yes, this is a problem. Before this happens, you will need to pick some new stars, and take a double round of sights - one for the fix, and one to establish a basis with the new stars. The other problem is that getting the compass bearing of a star is not that easy. I would recommend that anyone interested in emergency celestial navigation get a copy of "Particularized Navigation: How to Prevent Navigational Emergencies" by Francis Wright, which shows how to do "good enough" navigation with paper sextants, etc. Unfortunately, its long out of print, so a bit of work would be needed to adjust some of the tables to current dates. BTW, I own three sextants (two WWII vintage, one antique) plus two "lifeboat" sextants, but I haven't taken a sight on board in a dozen years. |
celestrial navigation anyone?
Bruce in Bangkok wrote:
On Sun, 20 Apr 2008 18:08:02 -0700, Gordon wrote: Dutton wrote: On Sun, 20 Apr 2008 11:26:00 -0700, "Capt. JG" wrote: Can you navigate (lat and long) at night with a sextant and a compass, but without a nautical almanac, sight reduction tables, the time of day, and without knowing the names of the stars? The sextant has an error, but you don't know what it is, just that it's off. You can keep your modern watch, but you just replaced the battery and the time is wrong. Why do you need all that stuff? The south pacific islander types followed the appropriate star in the appropriate constellation and got along just fine! Gordon Well, possible. Of course those times it didn't quite work we didn't hear about it... Bruce-in-Bangkok (correct email address for reply) Thats how they discovered new islands! They were knowm as the Fugawis! Like. "Where the Fugawi?" Gordon |
celestrial navigation anyone?
On Mon, 21 Apr 2008 10:10:13 -0400, Wayne.B
wrote: On Mon, 21 Apr 2008 18:55:22 +0700, Bruce in Bangkok wrote: That was not a sextant. It was called an octant. Here's one: http://www.icarusbooks.com/images/1458.jpg I've got no idea what that thing you referenced is but I can assure you that the devices carried aboard aircraft, at least until the 1970's was called a "Bubble Sextant" and didn't look a thing like your picture. Yes. http://www.warbirdsite.com/museumnavigation.html http://www.nautical-products.com/bubble-sextants.html http://www.physics.uq.edu.au/physics...ant_manual.pdf http://www.qmss.com/seastories/seastory05.html The device carried aboard USAF aircraft until the 1970's looked most like the bubble sextant shown as a US Navy bubble sextant Type A-12 at the top of the page in your reference http://www.warbirdsite.com/museumnavigation.html Note that it was a sextant, not an octant. Bruce-in-Bangkok (correct email address for reply) |
celestrial navigation anyone?
"Wayne.B" wrote in message
... On Sun, 20 Apr 2008 22:57:42 -0700, "Capt. JG" wrote: The advantage of this method is that it is incredibly easy to do. You don't even have to correct for refraction or dip. Even if your sextant has an error, it won't matter. Conceptually it works but has big issues in real life. As mentioned previously accurate star sights are only available for a few minutes at sunrise and sunset every day. The times of sunrise and sunset are changing every day from both seasonal variation and also from your own travel. And of course there are many days when no sights are possible because of overcast weather. You don't need accurate times for sunrise and sunset to make this work. You don't need to be dead on accurate if you're doing emergency navigation, which is what this would be good for. Getting close would be fine. And, you can use any couple of stars at night. -- "j" ganz @@ www.sailnow.com |
celestrial navigation anyone?
"Jeff" wrote in message ...
Capt. JG wrote: ... The disadvantage is that each position depends upon the previous one, so that small errors may build up to be large ones. No, you can go a number of days referencing the last fix. Don't understand... yes, you can go a number of days, but after that it seems to me it would start to get way off. If you are on a long voyage, you may find that the original stars are no longer visible at a time when they are useful. Yes, this is a problem. Thus, I good idea to take several batches of stars in your observation, so you can fall back on a second or third set. Before this happens, you will need to pick some new stars, and take a double round of sights - one for the fix, and one to establish a basis with the new stars. The other problem is that getting the compass bearing of a star is not that easy. Well, yes... that hard any time... I would recommend that anyone interested in emergency celestial navigation get a copy of "Particularized Navigation: How to Prevent Navigational Emergencies" by Francis Wright, which shows how to do "good enough" navigation with paper sextants, etc. Unfortunately, its long out of print, so a bit of work would be needed to adjust some of the tables to current dates. BTW, I own three sextants (two WWII vintage, one antique) plus two "lifeboat" sextants, but I haven't taken a sight on board in a dozen years. -- "j" ganz @@ www.sailnow.com |
celestrial navigation anyone?
"Dennis Pogson" wrote in message
... They look great on the mantleshelf. A wow at cocktail parties. Buy plenty of Brasso. Dennis. I'd like to keep mine aboard... a good talking point for students. -- "j" ganz @@ www.sailnow.com |
celestrial navigation anyone?
Really?
http://americanhistory.si.edu/collec...dnumber=451517 Catalogue number: AF*59057-N Inscriptions: "U.S. ARMY AIR CORPS / AIRCRAFT OCTANT / TYPE NO. A-7 SERIAL NO. A0-42-132 / SPECIFICATION NO. 94-27747A / ORDER NO. AC-17520 / MFR'S ASSY. DWG. NO. 3003-B / BENDIX AVIATION CORPORATION / PIONEER INSTRUMENT DIVISION / BENDIX, NEW JERSEY, U.S.A." and "MFR'D UNDER ONE OR MORE OF THE /FOLLOWING PATENT NOS. / 1556994 1674550 1970543 / 2221152 DES. 85912 / BENDIX AVIATION CORPORATION / PIONEER INSTRUMENT DIVISION / BENDIX, NEW JERSEY, U.S.A." Another aircraft octant: http://americanhistory.si.edu/collec...dnumber=123408 There are a number of aircraft octants for sale he http://www.paxp.com/mac/navtrak/sextants.html#used_m And another octant: http://americanhistory.si.edu/collec...dnumber=451519 Are you certain they were really sextants on those naval aircraft? We used an octant aboard a P-2. In maritime history octants were the predecessor of sextants. Octants have several distinct advantages over the sextant for use in aircraft. If you are experienced in the use of both you can really understand why. Perhaps your memory is not reliable. |
celestrial navigation anyone?
"Capt. JG" wrote in message news:89ydnfGc1fm5XJHVnZ2dnUVZ_vOdnZ2d@bayareasolut ions... "Dennis Pogson" wrote in message ... They look great on the mantleshelf. A wow at cocktail parties. Buy plenty of Brasso. Dennis. I'd like to keep mine aboard... a good talking point for students. -- "j" ganz @@ www.sailnow.com Just don't look through it backwards, upside down or leave the lens cap on it. http://www.galaksija.com/znakovi/clinton_binoculars.jpg |
celestrial navigation anyone?
"Roger Helio" wrote in message ... "Wayne.B" wrote in message ... It might be possible but I doubt it. There used to be a sextant designed for aircraft navigation in WW II that used an artificial horizon of sorts but those guys were happy to know where they were within 20 miles or so. That was not a sextant. It was called an octant. Here's one: http://www.icarusbooks.com/images/1458.jpg That is not an octant. It looks like a bubble sextant as used on aircraft.. An octant is exactly the same as a sextant except that is is constructed to read to 45 degrees against a sextant's 60. A sextant can therefore measure a wider angle than an octant. .. I have an octant that my grandfather used. It is made of ebony and has ivory engraved scale read with a vernier, but in all essential respects is identical to a sextant. |
celestrial navigation anyone?
Capt. JG wrote:
"Jeff" wrote in message ... Capt. JG wrote: ... The disadvantage is that each position depends upon the previous one, so that small errors may build up to be large ones. No, you can go a number of days referencing the last fix. Don't understand... yes, you can go a number of days, but after that it seems to me it would start to get way off. If you start with a fix, you don't accumulate error each day, only when you change stars. In other words, as long as you can use the same set of stars, you only have one sight's worth of error. In theory, if you have a large number of stars, you can go quite a while, since three good LOPs would count as a new fix. |
celestrial navigation anyone?
"Jeff" wrote in message ... If you start with a fix, you don't accumulate error each day, only when you change stars. In other words, as long as you can use the same set of stars, you only have one sight's worth of error. In theory, if you have a large number of stars, you can go quite a while, since three good LOPs would count as a new fix. Please don't say "fix" in front of Capt. JG. He might be inclined to suffer a relapse. -- Gregory Hall |
celestrial navigation anyone?
"Jeff" wrote in message ...
Capt. JG wrote: "Jeff" wrote in message ... Capt. JG wrote: ... The disadvantage is that each position depends upon the previous one, so that small errors may build up to be large ones. No, you can go a number of days referencing the last fix. Don't understand... yes, you can go a number of days, but after that it seems to me it would start to get way off. If you start with a fix, you don't accumulate error each day, only when you change stars. In other words, as long as you can use the same set of stars, you only have one sight's worth of error. In theory, if you have a large number of stars, you can go quite a while, since three good LOPs would count as a new fix. Yes, absolutely. My point was that 1) you're going to have to use multiple sets and 2) if you're inaccurate in your observation, this will translate into larger and larger errors later.... well, unless you only make one error. -- "j" ganz @@ www.sailnow.com |
celestrial navigation anyone?
"Edgar" wrote in message ... "Roger Helio" wrote in message ... "Wayne.B" wrote in message ... It might be possible but I doubt it. There used to be a sextant designed for aircraft navigation in WW II that used an artificial horizon of sorts but those guys were happy to know where they were within 20 miles or so. That was not a sextant. It was called an octant. Here's one: http://www.icarusbooks.com/images/1458.jpg That is not an octant. It looks like a bubble sextant as used on aircraft.. An octant is exactly the same as a sextant except that is is constructed to read to 45 degrees against a sextant's 60. A sextant can therefore measure a wider angle than an octant. . I have an octant that my grandfather used. It is made of ebony and has ivory engraved scale read with a vernier, but in all essential respects is identical to a sextant. It came from this page: http://www.icarusbooks.com/nonpaper.htm Click on the link CS1458 "Aircraft octant". Here's one on sale at eBay: http://cgi.ebay.com/WWII-NAVY-OCTANT...QQcmdZViewItem Here's a US Navy manual on them: http://cgi.ebay.com/SEXTANT-OCTANT-M...2em118Q2el1247 Here's another manual: http://cgi.ebay.com/Link-Bubble-Sext...2em118Q2el1247 Amelia Earhardt used an octant. Eddie Rickenbacker used one on his B-17. Octants were standard issue on B-17s. All US military aviation navigators used octants. What type of navigation uses a radiant? A radiant is an "octant" that covers 360 degrees. That will certainly stump all of you since no one even knew of the existence of an octant. (Hint: octants are top secret, only I know about them!). The term "sextant" was used for these devices so as not to confuse those of minimal mental capacity, apparently for good reason. |
celestrial navigation anyone?
wrote in message
... On Mon, 21 Apr 2008 14:10:51 -0700, "Capt. JG" wrote: "Jeff" wrote in message ... Capt. JG wrote: "Jeff" wrote in message ... Capt. JG wrote: ... The disadvantage is that each position depends upon the previous one, so that small errors may build up to be large ones. No, you can go a number of days referencing the last fix. Don't understand... yes, you can go a number of days, but after that it seems to me it would start to get way off. If you start with a fix, you don't accumulate error each day, only when you change stars. In other words, as long as you can use the same set of stars, you only have one sight's worth of error. In theory, if you have a large number of stars, you can go quite a while, since three good LOPs would count as a new fix. Yes, absolutely. My point was that 1) you're going to have to use multiple sets and 2) if you're inaccurate in your observation, this will translate into larger and larger errors later.... well, unless you only make one error. I think the typo in the subject line is making more and more sense. :') Heh... and apparently no one else noticed it. -- "j" ganz @@ www.sailnow.com |
celestrial navigation anyone?
"Capt. JG" wrote in message news:6bmdnauSu96riJDVnZ2dnUVZ_hmtnZ2d@bayareasolut ions... wrote in message ... On Mon, 21 Apr 2008 14:10:51 -0700, "Capt. JG" wrote: "Jeff" wrote in message ... Capt. JG wrote: "Jeff" wrote in message ... Capt. JG wrote: ... The disadvantage is that each position depends upon the previous one, so that small errors may build up to be large ones. No, you can go a number of days referencing the last fix. Don't understand... yes, you can go a number of days, but after that it seems to me it would start to get way off. If you start with a fix, you don't accumulate error each day, only when you change stars. In other words, as long as you can use the same set of stars, you only have one sight's worth of error. In theory, if you have a large number of stars, you can go quite a while, since three good LOPs would count as a new fix. Yes, absolutely. My point was that 1) you're going to have to use multiple sets and 2) if you're inaccurate in your observation, this will translate into larger and larger errors later.... well, unless you only make one error. I think the typo in the subject line is making more and more sense. :') Heh... and apparently no one else noticed it. What a twit! Only those with self-imposed blinders in the form of kill files didn't notice where I picked up on it and called you an idiot on day one. Wilbur Hubbard |
celestrial navigation anyone?
Not sure what you mean about not being able to use it at night... What about the artificial horizon common on modern sextants? http://en.wikipedia.org/wiki/Sextant I'm somewhat familiar with the Davis models... thinking about playing around with the 25. I have a Carl Zeiss "Yachtmaster" which does not have any artificial horizon and have yet to see a marine sextant that does. Bought it second hand in its wooden box 20 years ago for NZ$450. For sight reduction tables for sun, moon and stars I now use my O2 phone/PDA with a neat little programme (Bruce, please note the CORRECT and civilised spelling of "programme"). Yes, I know, a lightning strike could take that out too but I throw it in the oven with the some of the other gear when lightning gets too close. Anyway, there is always the backup of donning knee pads and grovelling to God. About once a year I get the urge to keep up my skills in case of such as a lightning strike, turn off all instruments for a few days and take sights. Peter |
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