Great video series. I have no practical use for this, but being a fan of Forrester and O'Brien, I've always wanted to understand more about how this worked. One can really appreciate how much harder it would have been in the Age of Sail without calculators or accurate chronometers....
Longitude easy at night For the Northern hemisphere, longitude for me is easy. If you can measure the Local Hour Angle of a star on the sky to an accuracy of 4 minutes or less you can get a longitude that is one degree or less from the observing position. A slight alteration of the calculation on page 279 of the Nautical Almanac and we have this. Longitude = GST - ( RA + LHA ) or LHA = GST - ( RA + Longitude) Where GST = Greenwich Siderial Time = GHA Aries. RA = the Right Ascension of the selected star. By using Polaris as the pivot point of a star clock and a plumb bob string for a meridian reference I've been getting longitudes to less than one degree easily from a list of 30 stars around Polaris. If measuring the LHA Westward, counter clockwise from the meridian upper branch, this is the angle to be added to the RA of the selected star. If measuring the LHA Eastward, clockwise, subtract LHA from RA. This gives Local Meridian Time, or Local Siderial Time. Then subtract LST from GST to get the GHA of the observing position. LHA can be measured in either time or degrees. This reduces to a minimum the time, math, materials, and paperwork needed to get something of a longitude, even if the observing position is not known. Just thought I would tell the world in case anyone is interested.
Very good explanation. A trig' ready-reckoner could be useful for the final chart fix perhaps (or, a scientific calculator). I've just returned from a trip on the "Royal Clipper" (Caribbean) and the navigating officer took me through their star maps and sextant use for Sirius, Betelgeuse and the Big Dipper (Plough). Unfortunately, the Southern Cross wasn't visible those nights.....Nice to know they can still do it the 'old fashioned' way ! I did also practice taking bearings from the ship's port compass which was gimballed and had very good sighting rings.
Are there any reliable methods to simplify this process? I am thinking about shooting the sun at noon which gives us our longitude more directly, or shooting polaris, which is usually directly to the north. Are there any other shortcuts that can help us create a simpler fix?
The easiest way would be to calculate latitude at local apparent noon. Because you have the exact time (GMT) at which LAN occurred you can calculate your longitude.
@@marcg1686 The easiest, yes, but the longitude from a noon Sun sight is not so accurate. A morning and an evening sight with two position lines making an angle is better. Three PLs are even better still.
@@karhukivi You are of course correct. The more PLs the better. However, we should not dismiss the basic utility of the intercept method, a single sight should be enough to get you within 20 nautical miles of your DR. You've been around for several years now. I've seen your comments oftentimes. Seems like you are looking out for flatwits, smearing themselves across the comments section of celnav videos. 👍 How is your MK15 holding up? I don't see much of a difference between my MK 15 and my Cassens & Plaths.
@@marcg1686 Probably wasting my time but you never know, some of them are just trying to be clever and are what the psychologists term "wilfully ignorant" which is setting them on the road to failure. They pop up in schools and even university lectures, so I just try to address their comments, failure rate is probably 99%, but that 1% might be worth the bother. The Mark 15 is way better now after I bought another mirror from Davis. I don't know what the problem was with the index error always changing but now it is very steady. I had a holiday on the S. Coast of the UK last year and spent a lot of time doing land-based fixes with Sun, Moon and planets and was getting position errors of 1-2 miles, which is as good as it gets. Stars were a challenge and misidentification was a big problem.
@@karhukivi I'm happy that your Mk15 is meeting expectations. I have two of them, one at home and the other at the office, and a Mk25. My Mk15s are my go to sextants.
Well done! If you're already marked your DR on the paper chart, then you can just use the compass rose, and your dividers, to measure 110' and 5.1NM from the DR. In that case you don't need the last calculation. Have you served the in merchant marine?
Yes filipino seafarer here nice video the last part is interesting yet the reality on board we will directly measured it in the latitude scale on the ploting chart. God bless my friend.
At the end, you forget to mention the clock. It is not just the position of stars, but the combination of stars and time, which lets you calculate your position.
Correct me if I am wrong but as far as I know the sunrise and sunset times are in local time not GMT. If it were GMT the sunrise of a location at 180E would be 15hours before, 1800 local time. Other then that on a northern course for 24hours would give you a flat of 4.8 degrees. Had it been on a course of 090 or 270 then the times wouldn’t have changed.
The times are converted to GMT purely for calculation purposes, to extract things like LHA, SHA, dec. etc. from the Almanac. So it would be the GMT time, at the time the sun is rising/setting in your longitude. This video is not about sun, it's about stars.
And by the time you're done with that, your ship has traveled 17 knots away from your sighted position with the rudder 3 degrees to starboard so you're steaming a curved path...
If you use the sight reduction tables to determine Hc and Z the entry arguments (lat, dec and LHA) need to be whole integer. This requires you change the DR to give you whole numbers. An example. Your DR Longitude is 35°17' W. The GHA of the Sun is 97°41'. You modify you DR Long to 35°41' so that the LHA equals 62°(97°41' - 35°41'). Because you modified your DR position it becomes an assumed position.
@@marcg1686 That is correct. If you use a calculator to do the reduction then there is no need to have exact integers and your assumed position can be the dead reckoning position or a convenient Lat/Long position on the chart.
Until you sail into an area like the Gulf of Aden where the hostile parties have spoofed the various GPS systems. The UK and US Navies are teaching celestial navigation for that very reason.
Are there any reliable methods to simplify this process? I am thinking about shooting the sun at noon which gives us our longitude more directly, or shooting polaris, which is usually directly to the north. Are there any other shortcuts that can help us create a simpler fix?
This video made me appreciate GPS even more.
Me too 😂
Hahaha lol
I mean like Bro! I can't recall the last time I punched Sin or Cos on any calculator. 😂😂🤣🤣
By the time i finished all this math id be 300 nautical miles off course 😅
Excellent video however i now know a lot more
Fellow dullard spotted, sup mate? 😂😂🤣🤣
The video: "Entertainment purposes only"
Me: continues to use this to prepare for celestial navigation exam
Hahah same here
What school do you go to that requires a celestial navigation exam?
Same
@@edwardfalk9997 I thought that all marine universities require this
y'all passed? 😂
Very useful videos.. im attending first class now, its refreshing
We don't give a FUCK about u attending whatsoever, u get it?
@@maideravenna8956 wow
Great video series. I have no practical use for this, but being a fan of Forrester and O'Brien, I've always wanted to understand more about how this worked. One can really appreciate how much harder it would have been in the Age of Sail without calculators or accurate chronometers....
Longitude easy at night
For the Northern hemisphere, longitude for me is easy. If you can measure the Local Hour Angle of a star on the sky to an accuracy of 4 minutes or less you can get a longitude that is one degree or less from the observing position. A slight alteration of the calculation on page 279 of the Nautical Almanac and we have this.
Longitude = GST - ( RA + LHA ) or
LHA = GST - ( RA + Longitude)
Where GST = Greenwich Siderial Time = GHA Aries.
RA = the Right Ascension of the selected star.
By using Polaris as the pivot point of a star clock and a plumb bob string for a meridian reference I've been getting longitudes to less than one degree easily from a list of 30 stars around Polaris. If measuring the LHA Westward, counter clockwise from the meridian upper branch, this is the angle to be added to the RA of the selected star. If measuring the LHA Eastward, clockwise, subtract LHA from RA. This gives Local Meridian Time, or Local Siderial Time. Then subtract LST from GST to get the GHA of the observing position. LHA can be measured in either time or degrees.
This reduces to a minimum the time, math, materials, and paperwork needed to get something of a longitude, even if the observing position is not known.
Just thought I would tell the world in case anyone is interested.
This is a great video. Good point about pre-calculating the altitudes and azimuths of the stars.
'Good point about pre-calculating the altitudes and azimuths of the stars.' Indeed, that is why HO249 Vol.1 is so popular.
Get it Right, or be lost at sea, forever.
Not for dummies, At All.
Very VERY Important!
Very good explanation. A trig' ready-reckoner could be useful for the final chart fix perhaps (or, a scientific calculator). I've just returned from a trip on the "Royal Clipper" (Caribbean) and the navigating officer took me through their star maps and sextant use for Sirius, Betelgeuse and the Big Dipper (Plough). Unfortunately, the Southern Cross wasn't visible those nights.....Nice to know they can still do it the 'old fashioned' way ! I did also practice taking bearings from the ship's port compass which was gimballed and had very good sighting rings.
As far i see video about this .. this is the best .. no debat
Thank you, great tutorial for Celestial navigation.
Are there any reliable methods to simplify this process? I am thinking about shooting the sun at noon which gives us our longitude more directly, or shooting polaris, which is usually directly to the north. Are there any other shortcuts that can help us create a simpler fix?
The easiest way would be to calculate latitude at local apparent noon. Because you have the exact time (GMT) at which LAN occurred you can calculate your longitude.
@@marcg1686 The easiest, yes, but the longitude from a noon Sun sight is not so accurate. A morning and an evening sight with two position lines making an angle is better. Three PLs are even better still.
@@karhukivi You are of course correct. The more PLs the better. However, we should not dismiss the basic utility of the intercept method, a single sight should be enough to get you within 20 nautical miles of your DR.
You've been around for several years now. I've seen your comments oftentimes.
Seems like you are looking out for flatwits, smearing themselves across the comments section of celnav videos. 👍
How is your MK15 holding up? I don't see much of a difference between my MK 15 and my Cassens & Plaths.
@@marcg1686 Probably wasting my time but you never know, some of them are just trying to be clever and are what the psychologists term "wilfully ignorant" which is setting them on the road to failure. They pop up in schools and even university lectures, so I just try to address their comments, failure rate is probably 99%, but that 1% might be worth the bother.
The Mark 15 is way better now after I bought another mirror from Davis. I don't know what the problem was with the index error always changing but now it is very steady. I had a holiday on the S. Coast of the UK last year and spent a lot of time doing land-based fixes with Sun, Moon and planets and was getting position errors of 1-2 miles, which is as good as it gets. Stars were a challenge and misidentification was a big problem.
@@karhukivi I'm happy that your Mk15 is meeting expectations. I have two of them, one at home and the other at the office, and a Mk25. My Mk15s are my go to sextants.
Well done! If you're already marked your DR on the paper chart, then you can just use the compass rose, and your dividers, to measure 110' and 5.1NM from the DR. In that case you don't need the last calculation. Have you served the in merchant marine?
Yes filipino seafarer here nice video the last part is interesting yet the reality on board we will directly measured it in the latitude scale on the ploting chart. God bless my friend.
When i can do this correctly and confidentially, deserve to be Captain and Commander, without a doubt
Thank you very much for the review of this subject.
"Other videos in this series …" - could you create a playlist maybe?
the most complicated explanation ever of a simple process
Don't let any salt water splash on your calculator while you mess with all those numbers!
Great job,
At the end, you forget to mention the clock. It is not just the position of stars, but the combination of stars and time, which lets you calculate your position.
Bloody hell that stuff's complicated. How did people ever invent this?!
The same people who made maps and studied astronomy and developed mathematics.
Thank you!
More over: instead of calculating final fix, u can reproduce a scaled mercator chart and track everything with a divider
Very nice
Maybe a good thing to do is to put the link to the playlist into the video description?
Great job
Correct me if I am wrong but as far as I know the sunrise and sunset times are in local time not GMT. If it were GMT the sunrise of a location at 180E would be 15hours before, 1800 local time. Other then that on a northern course for 24hours would give you a flat of 4.8 degrees. Had it been on a course of 090 or 270 then the times wouldn’t have changed.
The times are converted to GMT purely for calculation purposes, to extract things like LHA, SHA, dec. etc. from the Almanac. So it would be the GMT time, at the time the sun is rising/setting in your longitude. This video is not about sun, it's about stars.
is there a graphical mathod for this ?
Marq Saint Hilaire metod probably...
This is the graphical method.
@@hortigas1 this video is about Marc St Hiliare method.
I dont know what this is and i dont know how i got here. But i like it.
Thank you
Thnks
Playlist not showing up on your channel page
funny this channel starts with Casual
before GPS coordinates invented how navigators were getting latitude and longitude
I'm just going to follow the Hull to Zeebrugge ferry.
And by the time you're done with that, your ship has traveled 17 knots away from your sighted position with the rudder 3 degrees to starboard so you're steaming a curved path...
In 10 minutes? Your boat can do 100 kts?
I transfer the lines at the instant of last observation...
When to use dr and ap? Im kinda confused, others are using ap, and here he's using dr 🤔🤔
If you use the sight reduction tables to determine Hc and Z the entry arguments (lat, dec and LHA) need to be whole integer. This requires you change the DR to give you whole numbers.
An example. Your DR Longitude is 35°17' W. The GHA of the Sun is 97°41'.
You modify you DR Long to 35°41' so that the LHA equals 62°(97°41' - 35°41'). Because you modified your DR position it becomes an assumed position.
@@marcg1686 That is correct. If you use a calculator to do the reduction then there is no need to have exact integers and your assumed position can be the dead reckoning position or a convenient Lat/Long position on the chart.
This is hardcore math, bro.
haahahahahah
Oh man I would be so lost at sea.
GOD bless GPS
thank you!
Thank God for GPS, GLONASS, GALILEO and BeiDou system 😂😂
...and even the new Sky Map apps.
Until you sail into an area like the Gulf of Aden where the hostile parties have spoofed the various GPS systems. The UK and US Navies are teaching celestial navigation for that very reason.
haven't the slightest
First video in series: ruclips.net/video/nc_nSMtU0c0/видео.html
Very informative but my Brian give up
Eeee macarena
Jeepers, how often would you make a fix and how quickly could an experienced navigator do this?
Celestial fixes would only realistically be at sunset / sunrise
Are there any reliable methods to simplify this process? I am thinking about shooting the sun at noon which gives us our longitude more directly, or shooting polaris, which is usually directly to the north. Are there any other shortcuts that can help us create a simpler fix?
The noonday Sun fix is accurate for Latitude but not so good for Longitude as the top part of the curve seems to hang there for several minutes.
Jeepers, how often would you make a fix and how quickly could an experienced navigator do this?
It takes me about 10 minutes, but an experienced navigator could probably do it faster.
Very informative but my Brian give up