I've made up laminated 5x7 index cards with the 3 basic situations + the equinox and Lahaina Noon. I then wrote out the detailed procedure for crunching all the numbers and applying the 3 corrections on card stock and laminated that. I like your worksheet and I'll be replicating that as well. I keep all of this with the Nautical Almanac.
Thanks for a good description of using the noon sight to find latitude. Nit: At about 0:38 the video incorrectly calls the spot where the sun is directly overhead the declination. Actually that spot is generally called the geographic position (GP). The distance between the GP and equator is the declination.
Thanks Steve, you're exactly right. GP is defined by Greenwich Hour Angle and Declination. This video starts with declination and then we introduce GHA (and LHA) in the next video in the progression (Polaris). It's part of a series on our website that is also posted (in fragmented fashion) to TH-cam as well. Thanks for watching and for your comment! -Chris
For example, the instructor said, let’s say you have a HO of 45 degrees. First you have to find out if it is north or south. If it’s north, then the ZD will be south. Make sense?
Hello Amran, you will want to be outside shortly before local noon, when the sun is at its highest point. To determine when that is you can do a calculation or just observe the sun with the sextant. in the nautical almanac it lists the times of meridian passage which you can use to determine the time of local noon. Thanks!
Hi Chris, it is a good question - but being lost at sea would put us in more of a survival situation where we are unlikely to have a sextant and nautical almanac. I recommend a good book called "Emergency Navigation" by David Burch for these kind of situations - there are some cool tips and tricks in there to better understand how the sea and sky can help you know where you are. Thanks!
You're best bet is to have the tabulated values for the sun. Being lost I assume your electronics are down. If you can, keep an eye on the sun thru the noon hours, when it can be seen at 000 or 180 deg, mark the time. If the bearing is north, and the declination is north you know you are south of the tab dec. Fairly simple determination here, not rocket science. Computation from the time will allow the latitude portion of the problem and the GHA of the sun will be your longitude. How accurate the bearing is will have a large degree of how much error is obtained as well. Looking across a magnetic compass is not the best way to obtain a bearing. However, you're lost.. so being somewhere close in the math is way better than nothing at all. No sextant? make something an angle can be taken with. We know the suns dec only gets to about 25-26 deg max at summer and winter, Take a piece of plain paper, fold one corner down, thats 45 deg, fold over again makes 22.5 deg. Hold it to the sun by your eye, make a judgment call on how much angle the suns height is based on the known 22.5 deg fold. Take some time and mark the paper with various angles first. If you are a navigator, you should have a protractor at the chart table, use that as well.
I hate to answer this a year late, but the answer could help someone with the same question. If you have a compass and know what the date is, you can determine which hemisphere you are in based on the Sun's direction from your location. All you need to know is the dates of the spring and autumn equinox.
Is the HO (height observed) assigned a North or South descriptor? I ask because I just took a cel nav class and this part stumped me. The instructor said first find out if the HO is north or south, and whatever the ZD is, you will know it’s the opposite. Does that make sense?
No. Ho is the Observed Height, or Altitude (the angle taken from the sextant). The importance of your Latitude being North or South is because there are 3 cases involved with LAN determination of Latitude. Case 1 DR Lat > Dec Lat = Z Dist + Dec Case 2 DR Lat contrary to Dec Lat = Z Dist - Dec Case 3 DR Lat < Dec Lat = Dec - Z Dist So knowing if you are the same or opposite latitude of the Declination will determine which case applies.
Hello Richard - this will depend on your approximate location but the short answer is towards the sun. Depending on your hemisphere and season, it may be north or south, but those are the only two choices. Good luck!
Shouldn't you take multiple sights around noon and plot it in a graph to find the peak of the curve? As you are moving your longitude is changing so you never know what ut/gmt is your local noon. But the highest altitude or lowest zenith distance of the sun would. And you would be able to work back that time from your altitude/zenith distance chart.
Hi Valenorious, yes indeed that is a great technique to ensure you have the best reading possible. Generally your longitude is changing much slower than the sun's longitude but you are right that is a good way to be super accurate. Thanks!
I REALLY HATE THAT THE "LORDS" OF youtube HAVE FORCED ME TO upgrade TO THEIR NEWEST "Buggie" version of their software! THE OLD ONE WAS WORKING JUST FINE! BUT THIS? PURE KRAP!
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I've made up laminated 5x7 index cards with the 3 basic situations + the equinox and Lahaina Noon. I then wrote out the detailed procedure for crunching all the numbers and applying the 3 corrections on card stock and laminated that. I like your worksheet and I'll be replicating that as well. I keep all of this with the Nautical Almanac.
I have been all over the net ,books etc and have struggled until now .Thank you for such a clear explanation .
Equally excellent instruction, thanks again.
So so so so so SO helpful - thank you!
You rock Chris.
Thanks for a good description of using the noon sight to find latitude. Nit: At about 0:38 the video incorrectly calls the spot where the sun is directly overhead the declination. Actually that spot is generally called the geographic position (GP). The distance between the GP and equator is the declination.
Thanks Steve, you're exactly right. GP is defined by Greenwich Hour Angle and Declination. This video starts with declination and then we introduce GHA (and LHA) in the next video in the progression (Polaris). It's part of a series on our website that is also posted (in fragmented fashion) to TH-cam as well. Thanks for watching and for your comment! -Chris
Thanks! So helpful
Nicely explained.
You are great practical navigator
Thank you!
For example, the instructor said, let’s say you have a HO of 45 degrees. First you have to find out if it is north or south. If it’s north, then the ZD will be south. Make sense?
Thank a lot for your explination,
Could you please tell me, what time you should observe the Sun?
Hello Amran, you will want to be outside shortly before local noon, when the sun is at its highest point. To determine when that is you can do a calculation or just observe the sun with the sextant. in the nautical almanac it lists the times of meridian passage which you can use to determine the time of local noon. Thanks!
great
Great video , what happens if you're lost at sea and you dont know if you're north or south of the equator ?
Hi Chris, it is a good question - but being lost at sea would put us in more of a survival situation where we are unlikely to have a sextant and nautical almanac. I recommend a good book called "Emergency Navigation" by David Burch for these kind of situations - there are some cool tips and tricks in there to better understand how the sea and sky can help you know where you are. Thanks!
You're best bet is to have the tabulated values for the sun. Being lost I assume your electronics are down. If you can, keep an eye on the sun thru the noon hours, when it can be seen at 000 or 180 deg, mark the time. If the bearing is north, and the declination is north you know you are south of the tab dec. Fairly simple determination here, not rocket science. Computation from the time will allow the latitude portion of the problem and the GHA of the sun will be your longitude. How accurate the bearing is will have a large degree of how much error is obtained as well. Looking across a magnetic compass is not the best way to obtain a bearing. However, you're lost.. so being somewhere close in the math is way better than nothing at all. No sextant? make something an angle can be taken with. We know the suns dec only gets to about 25-26 deg max at summer and winter, Take a piece of plain paper, fold one corner down, thats 45 deg, fold over again makes 22.5 deg. Hold it to the sun by your eye, make a judgment call on how much angle the suns height is based on the known 22.5 deg fold. Take some time and mark the paper with various angles first. If you are a navigator, you should have a protractor at the chart table, use that as well.
I hate to answer this a year late, but the answer could help someone with the same question. If you have a compass and know what the date is, you can determine which hemisphere you are in based on the Sun's direction from your location. All you need to know is the dates of the spring and autumn equinox.
That is the reason that a Rolex watch is a navigational instrument not a piece of jewelry.
Is the HO (height observed) assigned a North or South descriptor? I ask because I just took a cel nav class and this part stumped me. The instructor said first find out if the HO is north or south, and whatever the ZD is, you will know it’s the opposite. Does that make sense?
No. Ho is the Observed Height, or Altitude (the angle taken from the sextant). The importance of your Latitude being North or South is because there are 3 cases involved with LAN determination of Latitude.
Case 1 DR Lat > Dec Lat = Z Dist + Dec
Case 2 DR Lat contrary to Dec Lat = Z Dist - Dec
Case 3 DR Lat < Dec Lat = Dec - Z Dist
So knowing if you are the same or opposite latitude of the Declination will determine which case applies.
The sight the you took with the sextant should be first corrected right? Same as with the declination by using the d factor
Which direction should you point the sextant to take the noon site?
Hello Richard - this will depend on your approximate location but the short answer is towards the sun. Depending on your hemisphere and season, it may be north or south, but those are the only two choices. Good luck!
Thanks!
How do u know that the sun is just below or above you??
Shouldn't you take multiple sights around noon and plot it in a graph to find the peak of the curve? As you are moving your longitude is changing so you never know what ut/gmt is your local noon. But the highest altitude or lowest zenith distance of the sun would. And you would be able to work back that time from your altitude/zenith distance chart.
Hi Valenorious, yes indeed that is a great technique to ensure you have the best reading possible. Generally your longitude is changing much slower than the sun's longitude but you are right that is a good way to be super accurate. Thanks!
I don’t understand how do you know when to add or subtract the declination
It's explained beginning 3:26
I REALLY HATE THAT THE "LORDS" OF youtube HAVE FORCED ME TO upgrade TO THEIR NEWEST "Buggie" version of their software!
THE OLD ONE WAS WORKING JUST FINE!
BUT THIS?
PURE KRAP!