Basics Of Navigation

Question 1

Earths circumference is

Answer 1

21,600NM/40,000KM

Question 2

Parallels of Latitude measure a co-ordinates’ N/S location as the angle between

Answer 2

The equator and the given parallel (up to 90^ North or South)

Question 3

Meridians of Longitude measure a coordinates, E/W location as the angle between

Answer 3

The prime meridian and the given meridian (up to 180^ east or west)

Question 4

Grid co-ordinates are measured in

Answer 4

Latitude then Longitude in Degrees^ and minutes’,

eg N45^22.4’, W004^55.6’
*there are 60 minutes in one degree

Question 5

To measure change of latitude in the same hemisphere, or change of longitude within same half of the earth (E/W),

Answer 5

Subtract

Question 6

To measure change of latitude between different hemispheres, or change of longitude between East and West,

Answer 6

Add

Question 7

Ratio of ellipticity gives distortion value of

Answer 7

1. 0033 difference between geocentric and geodetic measurement.
   * geodetic used in charts
   * * greatest difference at 45^N/S
   * ** smallest difference at poles and equator

Question 8

1 minute longitude or latitude at equator only =

Answer 8

1NM or 1.852km or 6080 feet

Question 9

Departure (NM)=

Answer 9

Change of Longitude (mins) x CosLat

Question 10

Direction is measured as

Answer 10

The angle from a datum

Question 11

A Great Circle is

Answer 11

The surface line of any plane intersecting a sphere through its center, and is the shortest distance connecting two points.

Question 12

Unusual cases of a great circle are

Answer 12

Meridian+antimeridian and equator, as they do not have changing track

Question 13

Except for the equator, every great circle lies

Answer 13

Half in the NH and half in the SH (vertices 180^ apart in longitude and equal in latitude)

Question 14

To calculate convergency,

Answer 14

Convergency (^)=ChLong (^) x Sin Mean Lat

Question 15

A rhumb line is

Answer 15

A line of constant direction, measuring the same angle at any meridian it crosses.

Question 16

A rhumb line lies

Answer 16

On the equatorial side of a great circle line.

Question 17

Average great circle true track between two points is equal to rhumb line true track. Conversion angle converts GC to RL

Answer 17

Conversion angle = 1/2 convergency angle

Question 18

Chlong (mins) =

Answer 18

Departure (NM) / Cos Lat

Question 19

To calculate distance along a meridian/antimeridian,

Answer 19

Distance (NM) =ChLat (^) x 60

Question 20

Definition of convergency:

Answer 20

1. Change of Great Circle Track between 2 points

2. Angle of inclination between two meridians at a selected latitude

Question 21

Representative Fractions:

Answer 21

• Use same unit of measurement throughout equation and are this dimensionless
• Are expressed as 1/denominator

Question 22

Scale Equation

Answer 22

Scale = Chart Distance/Earth Distance

1NM = 1.852KM = 6080 feet
1 inch = 2.55 cm

Large scale = large zoom factor
Small scale = small zoom factor

Question 23

Keplers Laws

Answer 23

1. Elliptical orbit of Earth around the Sun, with the Sun in one foci.
2. Radius vector sweeps out equal area in equal time ( earth slower at aphelion, thus travels less in orbit.

Question 24

Perihelion

Answer 24

Earth closest to sun (around Jan)

Question 25

Aphelion

Answer 25

Earth furthest from sun ( July)

Question 26

Variation in length of day and night is caused by

Answer 26

• the inclination of the ecliptic to the equator

- latitude

Question 27

Declination is defined as

Answer 27

The angle between the equinoctial and a line joining the earth to the sun

Question 28

Highest declination of the sun throughout the year causes:

Answer 28

A zenith once a year in each tropicwhen the sun reaches 90^ over the horizon.
Tropic of Cancer (23.5^ North) Jun 22
Tropic of Capricorn (23.5^ South) Dec 22

Question 29

Celestial equivalent of longitude

Answer 29

LHA Local Hour Angle
GHA Greenwich Hour Angle
* measure westerly and only correct for given time.

Question 30

Celestial equivalent of latitude

Answer 30

Declination north or south of the equinoctal

Question 31

Polar circles

Answer 31

Higher then 60.5^: summer days of constant twilight
Higher than 65.5^: summer days where sun doesnt set
Higher than 66.5^: winter days where sun doesnt rise

Question 32

A civil day

Answer 32

360^ rotation in 24 hours
15^ rotation in 1 hour
1^ rotation in 4 mins

Question 33

Arc to time conversion

Answer 33

Longitude / 15 = Time difference in LT

Question 34

When converting LMT to LMT

Answer 34

1. Longitude West, UTC Best, Longitude East, UTC least
2. Always convert through UTC using Date Hour Minute table
3. Passing through 180 E/W: from West to East, add one day, from East to West subtract one day

Question 35

Standard Time

Answer 35

1. Is set by each country as stated in Air Almanac and does not necessarily follow 1 hour for each 15^
2. May lead to 13 hours difference with UTC
3. In Daylight Saving Time in summer, Add one hour to UTC

Question 36

Moment of Sunrise/Sunset

Answer 36

Top tip of sun rises, 34’ refraction+ 16’ semi diameter = center of sun 50’ below sensible horizon

Question 37

Civil twilight

Answer 37

6^ below sensible horizon until sunset/sunrise

* varies from 21 mins at equinox at equator to longer at higher latitudes/ summer.