Earth, position, distance Flashcards
What is the realistic shape of the earth?
GEOID. using the fluctuating MSL
What is the shape of the earth used for navigation?
Ellipsoid. WGS 84 model
How do we measure latitude values in the ellipsoid (wgs 84 model)?
GEODETIC Latitudes. The local perpendicular to the equatorial plane.
What angle is the spin axis of the earth? aka the angle between the plane of the eliptic and the equator.
23.5 degress
Define the compression ratio
the ratio between the equatorial radius (the semi major) and the pole radius (semi minor)
What is the compression ratio of earth?
1/298= 0.33%
How fast is the Earth rotating, in degrees?
15.04 degrees per hour
How does the axis tilt affect earth?
isolation/changing seasons
Duration of daylight
What is a Latitude?
horizontal lines running parallel to the equator. Small cricles that don’t intersect the centre.
What is a Longitude
Vertical lines that run between the poles. Also know as Meridians. they are semi great circles and unparallel.
What is the maximum angle of a longitude?
180 degrees. earth is split into E and W hemisphere of 180 degrees each.
How do we calculate differences in latitude in the same hemisphere?
subract the smallest value from the largest
How do we calculate latitude differences in different hemispheres?
add the values together
How to we caluclate differences in longitude?
add the values together. max of 180 degrees. If more, subtract from 360 to find the shortest route.
Define Antipode
Diametrically opposite position.
Latitude = swap N/S
Longitude = current and opposite value will make 180.
What is our unit of measure for distance? What does it equal?
Nautical Mile = 1 minute of latitude arc (1/60 a degree)
60 minutes/NM in 1 degree.
List the NM conversion to KM, STM, FT
1nm = 1.852km 1nm = 1.152 stm 1nm = 6076
What is the (equatorial) circumference of earth?
21,600nm
Where is the MAX arc distance?
where is the MIN arc difference?
Where is the average arc distance?
Max = 090 = 1.862km min = 000 = 1.843 average = roughly 45 = 1.852
What is Chlat?
How do we calculate the difference?
Chlat = Change in latitude along the same meridian
Subract the smaller from the larger to get Chlat degrees. multiply this by 60 to get NM
in reverse we can take the nm/60 = chlat degrees and add to start position.
How do we calculate Chlat across hemispheres?
We add the co-oridnates together and multiply by 60 to get NM (adding the pre-existing minutes after)
in reverse, we take the nm/60 = chlat degrees. add/subtract from start position. Going through equator/hemisphere will give us a negative figure. disregard the negative.
What do we do if our calculations take us through the poles?
the longitudinal (meridian) value becomes antipodal (adds upto 180)
the extra latitude over the pole needs subtracting from 90 and then 90 again.
define Chlong?
Chlong = change in longitude/meridian values
What is the formula for calculating Chlong?
departure = chlong minutes x CosLat
(chlong minutes = degree difference x 60)
‘departure’ distance is proportional to the cosine of latitue due to the converging of the meridians.
what is the formula for Chlong when working in reverse?
chlong minutes = departure/ CosLat
one step further, Chlong’/60 = Chlong degress
what is 1 minute of meridian arc at the equator?
2 metres more than lat 1.852km
What is the diameter of the Earth?
6880nm or 12,742km
