General Navigation - Coordinates and Distance Flashcards
What are the most common units used in horizontal navigation?
km, NM, ft
How long is a km in feet and inches?
3280 ft and 10 and 5/64th inches
How many feet in 1 NM?
6076.16 ft
How many km in 1 NM?
1.852 km
What’s the origin of the KM?
The Earth (10,000 KM from the equator to a pole)
Why is one degree of travel along a parallel of latitude not the same distance as along a meridian?
Because a parallel is not a circumference
As we move away from the equator the…distance decreases
East/west
Define the departure
The east/west distance (NOT the shortest distance)
How do we calculate east/west distance?
Departure (NM) = Change in Longitude (minutes) x Cosine of the Latitude
Unless you’re on the equator, one degree east/west is always…
Less than 60 NM
How do we calculate shortest distance when two longitudes are on opposite meridians? How can you check that the question is one which requires this calculation?
Add the latitudes and subtract the answer from 180°. The longitudes will add up to 180°.
What is a nautical mile longer than?
A statute mile.
From what was the unit of kilometers originally derived?
From the Earth itself.
How many kilometers are there from the equator to the pole?
10,000 km.
What is the Earth’s circumference in kilometers?
40,000 km.
How is one nautical mile defined?
As the distance subtended by one minute of arc on the Earth’s circumference.
How many nautical miles (NM) are there in one degree change of latitude?
60 NM.
What is the Earth’s circumference in nautical miles (NM)?
21,600 NM.
What is the distance from the equator to the pole in nautical miles (NM)?
5,400 NM.
How is the distance between 48°N and 49°N along the meridian described?
One degree, sixty minutes, or 60 NM.
What affects the distance between 010°W and 011°W?
The parallel of latitude is not a circumference; it is less than 60 NM.
What happens to the distance between meridians as latitude increases?
The distance decreases.
How do you find the distance along a meridian?
Add the change of latitude in minutes and convert to NM.
How do you convert km/hour to NM/hour or knots (KT)?
Use the number of feet in each unit: 890 km/hour ≈ 480 KT.
How is a change of latitude in degrees calculated for a given distance in NM?
Divide the NM by 60.
What does the east/west distance represent in navigation?
The east/west distance traveled, not the shortest distance.
What is the formula for calculating departure in NM?
Departure (NM) = Change of Longitude (minutes) x Cosine of the Latitude.
What is the one degree ‘box’ distance from north to south and east/west at the equator?
60 NM from north to south and 40 NM across the bottom.
What is the distance in an east/west direction along a parallel of latitude at 49°N?
Slightly smaller than 40 NM, about 39 NM.
What is the distance of one degree north/south and one degree east/west (the departure) always less than, unless you are on the equator?
Less than 60 NM.
What can we find by measuring the angle between points along a circumference of the Earth?
The distance between two points.
How is the distance between two latitudes found?
By finding the change of latitude.
How is the distance between points on the equator found?
By finding the change of longitude.
How do you find the angle between points measured at the center of the Earth?
By adding the latitudes and subtracting the total from 180°.
What is the distance corresponding to an angle of 40°?
2400 NM.
What assumptions are made for the purposes of calculating distances?
The Earth is a perfect sphere.
What is the actual shape of the Earth?
A squashed sphere, an ellipsoid.
What is the distance covered by one minute of arc at the poles, at 45°N and 45°S, and at the equator?
6107 ft at the poles (more than a NM), 6076 ft at 45°N and 45°S (exactly a NM), 6045 ft at the equator (less than a NM).
What do modern navigation systems compensate for?
The flattening of the Earth.
What error do older navigation systems list arising from the assumption that the Earth is round?
Latitude error.
