The Nautical Mile?.
Standard description of the Nautical Mile copied from a text book. "A Nautical Mile is the distance on the Earths surface subtended by one minute of latitude at the Earths centre".
Without complicating this further by referring to the distances..........
The Earth is an oblate spheroid having a slightly greater (+/- 13 miles) Earth centre to Equator radius than Earth centre to pole. Therefore you would expect an angle of 1 minute at the Earth centre subtended to the Equator would yield a nautical mile of greater distance than 1 minute subtended to the pole. In the case of the equator the radians are diverging for a greater distance.
However this is not the case as all references to the actual distance of a nautical mile (apart from the internationally recognised figure of 1852m which is a different issue) states a nautical mile at/near the pole is greater than at/near the equator.
I have been chewing this over for some time and am thinking the nautical mile has less to do with angles of 1 minute at the earth centre and more to do with the distance along an arc (earths surface) between 2 points where the curve alters by 1 minute. That is to say tangents drawn at the 2 points would create an angle of 1 minute where they meet/cross.
This relates to the earth/oblate spheroid as the flattening at the pole creates a flatter curve of the earth surface and therefore a greater distance between the 2 points required to create a 1 minute angle at the tangents. Conversely the more acute curve at/near the equator means a shorter distance between the 2 points.
I am unable to come up with a more plausible explanation?
Additionally the flatter curve at the pole suggests it is part of a circle of greater diameter than earth and the more acute curve at the equator suggests it is part of a circle of lesser diameter than earth.
Furthermore if the longer nautical mile (1 minute of arc) at the pole is subtended to the earth centre rather than its natural greater radius the angle created at the earth centre would be greater than 1 minute. Conversely if the shorter nautical mile at the equator is subtended to the earth centre the angle created will be less than 1 minute.
Please confirm the above or correct my understanding.
Many thanks
Mike
I think you can assume that the earth is treated as a sphere.
The nautical mile is 1/360 * 1/60 of the circumference.
The concept of the nautical mile can be a bit confusing, but I'll do my best to explain it step-by-step.
1. The standard definition of a nautical mile is the distance on the Earth's surface subtended by one minute of latitude at the Earth's center. So, in theory, if you were to draw a line from the Earth's center to any point on its surface, and then draw another line from that point to a point one minute of latitude away, the distance between those two points would be one nautical mile.
2. However, due to the Earth's shape, the distance between two points one minute of latitude away can actually vary depending on their location. As you mentioned, the Earth is an oblate spheroid, meaning it's slightly flattened at the poles and bulging at the equator.
3. The flattening at the poles creates a flatter curve on the Earth's surface, so the distance between two points one minute of latitude away at the poles would be greater than the distance between two points one minute of latitude away at the equator.
4. This means that, in practice, the nautical mile near the poles is greater than the nautical mile near the equator. This is in contrast to what you might expect if you simply used the definition of the nautical mile based on one minute of latitude at the Earth's center.
5. So, to summarize, the nautical mile is not solely based on angles of one minute at the Earth's center, but rather on the distance along an arc of the Earth's surface between two points where the curve changes by one minute.
I hope this explanation clarifies the concept of the nautical mile for you. Let me know if you have any further questions!
The concept of the nautical mile can be a bit confusing, so I'll try my best to explain it in a simplified manner.
The nautical mile is a unit of measurement commonly used in navigation and aviation. It is defined as the distance on the Earth's surface that is subtended by one minute of latitude. In other words, if you were to draw a line from a certain latitude point to another point one minute of latitude away, the distance along that line is one nautical mile.
You are correct in noting that the Earth is not a perfect sphere but rather an oblate spheroid, slightly flattened at the poles and bulging at the equator. This slight distortion affects the shape of the Earth's surface and can have an impact on how the nautical mile is measured.
When we consider the Earth's shape, we would expect that the distance between two latitude points that are one minute of latitude apart would be greater at the poles compared to the equator, due to the flatter curve at the poles. However, it is actually the opposite.
The reason for this discrepancy is that the nautical mile is not solely dependent on the angle of one minute of latitude at the Earth's center, but rather on the distance along the Earth's surface between two points where the curve of the Earth alters by one minute. This means that the nautical mile is influenced by the actual shape of the Earth's surface and not just by angles.
At the equator, the Earth's surface has a steeper curve, meaning that the distance between two points where the curve alters by one minute is shorter, resulting in a shorter nautical mile. Conversely, at the poles, where the Earth's surface is flatter, the distance between two points with a one-minute curve alteration is longer, resulting in a longer nautical mile.
In summary, the nautical mile is a measurement based on the distance along the Earth's surface rather than just the angle of one minute at the Earth's center. The larger nautical mile at or near the poles is due to the flatter curve of the Earth's surface, which requires a longer distance to create a one-minute alteration in the curve. The shorter nautical mile at or near the equator is a result of the more acute curve of the Earth's surface, requiring less distance to create a one-minute alteration.
I hope this explanation helps clarify the concept of the nautical mile. Let me know if you have any further questions or if there's anything else I can assist you with!