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FYI a Knot is standard for navigation world wide because the unit is standardized on earth's size. 1kt = 1 nautical mile per hour. 1 nautical mile = one minut

FYI a Knot is standard for navigation world wide because the unit is standardized on earth's size. 1kt = 1 nautical mile per hour. 1 nautical mile = one minute of Earth's longitude. Learned this in sailing class :) Wikipedia: "Worldwide, the knot is used in meteorology, and in maritime and air navigation—for example, a vessel travelling at 1 knot along a meridian travels approximately one minute of geographic latitude in one hour."

LeifCarrotson 10y ago
Latitude, not longitude - the length of one minute of longitude changes with your distance from the equator. Also, I am not sure how that's relevant to NOAA?
- Spooky23 10y ago
  NOAA is part of the Commerce Department and Oceanic is part of their name. An important consumer of the data are entities who navigate the sea and air. Both constituencies use knots and nautical miles.
  - kqr 10y ago
    > An important consumer of the data are entities who navigate the sea and air. You make it sound like birds and fish check in with the NOAA before planning migrations. Edit: and that they're really picky about units of measurement.
gilgoomesh 10y ago
Using "Knot" because it's tied to longitude and latitude is the exact point the metric system is designed to avoid: needless and inaccurate attachments between system of units and specific phenomena that actually complicate rather than simplify and hinder interoperation with every other system. As you state: 1. a knot is only approximately equal to 1 min of latitude per hour (there are numerous cases where it's unusably wrong) 2. doesn't really help for longitudinal travel 3. maps are continuously projected to favor this mediocre form of navigation instead of something more accurate (see Mercator projection) 4. you could easily put kilometre lines on your charts instead of minutes of latitude and fix all the previous problems
- Justin_K 10y ago
  That's going to work great when the earth goes back to being flat.
- Ultimatt 10y ago
  No Mercator projection is used because its the least weird conformal projection (you draw a straight line its really straight in the real world). If you are trying to plot a bearing at the scale of the planet you want to be using Mercator unless you are going over the pole :P That the same projection is then used for everything even when you don't need to preserve local angles isn't the fault of Mercator. That you think km lines on an atlas would be better than lat/long makes you crazy. A decimal day might be useful but a decimal year is not. A fractional decimal day is a completely useless reference of time for doing quantum mechanics, but perfectly reasonable for people planning their work. No one would get rid of the concept of "a day". A map that maybe only shows tens or hundreds of km might be fine but representing the whole world with an equal area map with all grid reference based on km isn't useful to many people who use maps a lot, especially as the world isn't describable in whole numbers of km! But does have absolute and continuous angles from the gravitational centre.
  - NickNameNick 10y ago
    Lines on a Mercator map aren't straight on a globe. They are constant-compass bearing, but that's not the same as straight. Also, as defined by the French academy of science ~1800, the meter is 1/10,000,000th the distance from the north pole to the equator, on the meridian through Paris.
    - kqr 10y ago
      Not sure what your metre comment is about, but it turned out that definition wasn't accurate enough to confidently state the speed of light, so the speed of light was set to 299792458 m/s and a metre is consequently the distance light travels in a 299792458th of a second. (The second is in turn precisely defined by particle physics.)
Redoubts 10y ago
> FYI a Knot is standard for navigation world wide because the unit is standardized on earth's size. Historically, a meter was too. A line of longitude is a little over 20,000km.
ghgr 10y ago
"1 nautical mile = one minute of Earth's longitude" ... along the Equator
- rtkwe 10y ago
  and at the poles. It's latitude that gets compressed at the poles.
  - Steuard 10y ago
    Going north means changing latitude to approach 90 degrees north latitude at the pole. Those degrees of latitude are evenly spaced in distance (s=rtheta, if theta is angle north of the equator). Going east means changing longitude, rising from -180 degrees to 180 and then resetting. Those degrees of longitude correspond to less and less distance at the poles (s=rcos(theta)*phi, if theta is angle north of the equator and phi is angle around the axis).
laxatives 10y ago
Should get a refund then. A minute of longitude near a pole is inches. Its a minute of latitude for a reason.
reacweb 10y ago
For air navigation, there is the exception of Russia (and ex URSS countries) where metric system was the norm. Each time I have encountered meteorology software, they were using m.s-1. It was a big source of confusion.
dhimes 10y ago
One minute of Latitude, not longitude. (I teach the class...)
anonymfus 10y ago
1 km is also one metrical minute (1/100 of grad, also "centigrade") of Earth's latitude.

LeifCarrotson 10y ago

Latitude, not longitude - the length of one minute of longitude changes with your distance from the equator. Also, I am not sure how that's relevant to NOAA?

Spooky23 10y ago
NOAA is part of the Commerce Department and Oceanic is part of their name. An important consumer of the data are entities who navigate the sea and air. Both constituencies use knots and nautical miles.
- kqr 10y ago
  > An important consumer of the data are entities who navigate the sea and air. You make it sound like birds and fish check in with the NOAA before planning migrations. Edit: and that they're really picky about units of measurement.

gilgoomesh 10y ago

Using "Knot" because it's tied to longitude and latitude is the exact point the metric system is designed to avoid: needless and inaccurate attachments between system of units and specific phenomena that actually complicate rather than simplify and hinder interoperation with every other system. As you state: 1. a knot is only approximately equal to 1 min of latitude per hour (there are numerous cases where it's unusably wrong) 2. doesn't really help for longitudinal travel 3. maps are continuously projected to favor this mediocre form of navigation instead of something more accurate (see Mercator projection) 4. you could easily put kilometre lines on your charts instead of minutes of latitude and fix all the previous problems

Justin_K 10y ago
That's going to work great when the earth goes back to being flat.
Ultimatt 10y ago
No Mercator projection is used because its the least weird conformal projection (you draw a straight line its really straight in the real world). If you are trying to plot a bearing at the scale of the planet you want to be using Mercator unless you are going over the pole :P That the same projection is then used for everything even when you don't need to preserve local angles isn't the fault of Mercator. That you think km lines on an atlas would be better than lat/long makes you crazy. A decimal day might be useful but a decimal year is not. A fractional decimal day is a completely useless reference of time for doing quantum mechanics, but perfectly reasonable for people planning their work. No one would get rid of the concept of "a day". A map that maybe only shows tens or hundreds of km might be fine but representing the whole world with an equal area map with all grid reference based on km isn't useful to many people who use maps a lot, especially as the world isn't describable in whole numbers of km! But does have absolute and continuous angles from the gravitational centre.
- NickNameNick 10y ago
  Lines on a Mercator map aren't straight on a globe. They are constant-compass bearing, but that's not the same as straight. Also, as defined by the French academy of science ~1800, the meter is 1/10,000,000th the distance from the north pole to the equator, on the meridian through Paris.
  - kqr 10y ago
    Not sure what your metre comment is about, but it turned out that definition wasn't accurate enough to confidently state the speed of light, so the speed of light was set to 299792458 m/s and a metre is consequently the distance light travels in a 299792458th of a second. (The second is in turn precisely defined by particle physics.)

Redoubts 10y ago

> FYI a Knot is standard for navigation world wide because the unit is standardized on earth's size. Historically, a meter was too. A line of longitude is a little over 20,000km.

ghgr 10y ago

"1 nautical mile = one minute of Earth's longitude" ... along the Equator

rtkwe 10y ago
and at the poles. It's latitude that gets compressed at the poles.
- Steuard 10y ago
  Going north means changing latitude to approach 90 degrees north latitude at the pole. Those degrees of latitude are evenly spaced in distance (s=rtheta, if theta is angle north of the equator). Going east means changing longitude, rising from -180 degrees to 180 and then resetting. Those degrees of longitude correspond to less and less distance at the poles (s=rcos(theta)*phi, if theta is angle north of the equator and phi is angle around the axis).

laxatives 10y ago

Should get a refund then. A minute of longitude near a pole is inches. Its a minute of latitude for a reason.

reacweb 10y ago

For air navigation, there is the exception of Russia (and ex URSS countries) where metric system was the norm. Each time I have encountered meteorology software, they were using m.s-1. It was a big source of confusion.

dhimes 10y ago

One minute of Latitude, not longitude. (I teach the class...)

anonymfus 10y ago

1 km is also one metrical minute (1/100 of grad, also "centigrade") of Earth's latitude.