My previous posts have dramatically improved my understanding of how a NM is derived but other questions have been raised:
In most books entitled "Pass your Day Skipper" or "Yachtmaster" or similar nautical/navigational publications Latitude is described and illustrated as the angular distance 0 degrees to 90 degrees either N or S of the equator and in the illustrations the angles are drawn using a common centre of the earth. Is it fair to assume this is an appropriate simplification of the more complex reality.
I am having difficulty assimilating what used to be my understanding ie. the simplified version and my new understanding the more complex version.
OR am I just becoming more confused?
Mike
Those drawings are simplified. The only reason that the "new" definition of the minute of latitude being arc disance subtended by one minute from the center of curvature is that satellite mapping has made it possible to accurately map the real Earth Surface. For surface navigation, one common center of the Earth is possible. Few folks navigating are at the S or N pole, and those who do use GPS.
Hello again Bob, Thanks for your reply. The point that has grabbed my attention now is you refer to the "NEW" definition of the minute of latitude. Things are slowly falling into place at this end. Do you happen to know when the "NEW" definition of latitude was introduced?
Mike
It couln't be done until we knew the shape of the Earth with some precision, in particular the semimajor and semiminor axis. WGS 84 is the system that defined these lengths with some precision. With that, the point of curvature could be determined, and thence the distance subtended.
http://en.wikipedia.org/wiki/WGS84
By the way, the international standard for a nautical mile is fixed as the average distance. All this is somewhat like mom's favorite apple pie recipe, it depends on who is eating, when, and what ingredients were available at cooking.
Hello Bob, love your analogy about mom's apple pie recipe.
Allow me to enter the NM debate at this point.
Do you happen to have a good explanation re the origin of the k in knots for "nautical miles per hour"?
http://mathforum.org/kb/message.jspa?messageID=1470195&tstart=0
This is as I learned it many years ago as a seaman.
That makes sense.
BTW, interesting thread.
It's completely natural to feel a bit confused when new information challenges your previous understanding. However, understanding latitude and its relationship with the Earth is actually quite straightforward once you have a clear explanation.
Latitude is indeed the angular distance, measured in degrees, north or south of the equator, which is defined as 0 degrees latitude. The concept of latitude is commonly simplified in educational materials by considering the Earth as a perfect sphere, with the angles drawn using a common center. This simplification helps beginners grasp the basic idea without getting overwhelmed by the intricacies of Earth's shape and geodesy.
In reality, the Earth is not a perfect sphere but an oblate spheroid. It bulges slightly at the equator and flattens at the poles due to its rotation. To accurately determine latitude, one must consider the Earth's actual shape. This involves taking into account the Earth's geodesy and measuring the angles from the center of mass rather than a common center.
So, to answer your question, the simplified version of latitude using a common center is a reasonable approximation for basic understanding. However, as you delve deeper into navigation and more advanced topics, it's essential to incorporate the complexities of Earth's shape for greater accuracy.
Don't worry if you find it challenging to assimilate the simplified and complex versions initially. Take your time to explore and understand both perspectives. Learning is often an iterative process, and with persistence, you will be able to reconcile the two understandings and enhance your overall knowledge of navigation.