Earth, position, distance

Question 1

What is the realistic shape of the earth?

Answer 1

GEOID. using the fluctuating MSL

Question 2

What is the shape of the earth used for navigation?

Answer 2

Ellipsoid. WGS 84 model

Question 3

How do we measure latitude values in the ellipsoid (wgs 84 model)?

Answer 3

GEODETIC Latitudes. The local perpendicular to the equatorial plane.

Question 4

What angle is the spin axis of the earth? aka the angle between the plane of the eliptic and the equator.

Answer 4

23.5 degress

Question 5

Define the compression ratio

Answer 5

the ratio between the equatorial radius (the semi major) and the pole radius (semi minor)

Question 6

What is the compression ratio of earth?

Answer 6

1/298= 0.33%

Question 7

How fast is the Earth rotating, in degrees?

Answer 7

15.04 degrees per hour

Question 8

How does the axis tilt affect earth?

Answer 8

isolation/changing seasons

Duration of daylight

Question 9

What is a Latitude?

Answer 9

horizontal lines running parallel to the equator. Small cricles that don’t intersect the centre.

Question 10

What is a Longitude

Answer 10

Vertical lines that run between the poles. Also know as Meridians. they are semi great circles and unparallel.

Question 11

What is the maximum angle of a longitude?

Answer 11

180 degrees. earth is split into E and W hemisphere of 180 degrees each.

Question 12

How do we calculate differences in latitude in the same hemisphere?

Answer 12

subract the smallest value from the largest

Question 13

How do we calculate latitude differences in different hemispheres?

Answer 13

add the values together

Question 14

How to we caluclate differences in longitude?

Answer 14

add the values together. max of 180 degrees. If more, subtract from 360 to find the shortest route.

Question 15

Define Antipode

Answer 15

Diametrically opposite position.

Latitude = swap N/S

Longitude = current and opposite value will make 180.

Question 16

What is our unit of measure for distance? What does it equal?

Answer 16

Nautical Mile = 1 minute of latitude arc (1/60 a degree)

60 minutes/NM in 1 degree.

Question 17

List the NM conversion to KM, STM, FT

Answer 17

1nm = 1.852km
1nm = 1.152 stm
1nm = 6076

Question 18

What is the (equatorial) circumference of earth?

Answer 18

21,600nm

Question 19

Where is the MAX arc distance?
where is the MIN arc difference?
Where is the average arc distance?

Answer 19

Max = 090 = 1.862km
min = 000 = 1.843
average = roughly 45 = 1.852

Question 20

What is Chlat?

How do we calculate the difference?

Answer 20

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.

Question 21

How do we calculate Chlat across hemispheres?

Answer 21

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.

Question 22

What do we do if our calculations take us through the poles?

Answer 22

the longitudinal (meridian) value becomes antipodal (adds upto 180)

the extra latitude over the pole needs subtracting from 90 and then 90 again.

Question 23

define Chlong?

Answer 23

Chlong = change in longitude/meridian values

Question 24

What is the formula for calculating Chlong?

Answer 24

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.

Question 25

what is the formula for Chlong when working in reverse?

Answer 25

chlong minutes = departure/ CosLat

one step further, Chlong’/60 = Chlong degress

Question 26

what is 1 minute of meridian arc at the equator?

Answer 26

2 metres more than lat 1.852km

Question 27

What is the diameter of the Earth?

Answer 27

6880nm or 12,742km