Basics Of Navigation Flashcards
Earths circumference is
21,600NM/40,000KM
Parallels of Latitude measure a co-ordinates’ N/S location as the angle between
The equator and the given parallel (up to 90^ North or South)
Meridians of Longitude measure a coordinates, E/W location as the angle between
The prime meridian and the given meridian (up to 180^ east or west)
Grid co-ordinates are measured in
Latitude then Longitude in Degrees^ and minutes’,
eg N45^22.4’, W004^55.6’
*there are 60 minutes in one degree
To measure change of latitude in the same hemisphere, or change of longitude within same half of the earth (E/W),
Subtract
To measure change of latitude between different hemispheres, or change of longitude between East and West,
Add
Ratio of ellipticity gives distortion value of
- 0033 difference between geocentric and geodetic measurement.
* geodetic used in charts
* * greatest difference at 45^N/S
* ** smallest difference at poles and equator
1 minute longitude or latitude at equator only =
1NM or 1.852km or 6080 feet
Departure (NM)=
Change of Longitude (mins) x CosLat
Direction is measured as
The angle from a datum
A Great Circle is
The surface line of any plane intersecting a sphere through its center, and is the shortest distance connecting two points.
Unusual cases of a great circle are
Meridian+antimeridian and equator, as they do not have changing track
Except for the equator, every great circle lies
Half in the NH and half in the SH (vertices 180^ apart in longitude and equal in latitude)
To calculate convergency,
Convergency (^)=ChLong (^) x Sin Mean Lat
A rhumb line is
A line of constant direction, measuring the same angle at any meridian it crosses.
A rhumb line lies
On the equatorial side of a great circle line.
Average great circle true track between two points is equal to rhumb line true track. Conversion angle converts GC to RL
Conversion angle = 1/2 convergency angle
Chlong (mins) =
Departure (NM) / Cos Lat
To calculate distance along a meridian/antimeridian,
Distance (NM) =ChLat (^) x 60
Definition of convergency:
- Change of Great Circle Track between 2 points
2. Angle of inclination between two meridians at a selected latitude
Representative Fractions:
- Use same unit of measurement throughout equation and are this dimensionless
- Are expressed as 1/denominator
Scale Equation
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
Keplers Laws
- Elliptical orbit of Earth around the Sun, with the Sun in one foci.
- Radius vector sweeps out equal area in equal time ( earth slower at aphelion, thus travels less in orbit.
Perihelion
Earth closest to sun (around Jan)
Aphelion
Earth furthest from sun ( July)
Variation in length of day and night is caused by
- the inclination of the ecliptic to the equator
- latitude
Declination is defined as
The angle between the equinoctial and a line joining the earth to the sun
Highest declination of the sun throughout the year causes:
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
Celestial equivalent of longitude
LHA Local Hour Angle
GHA Greenwich Hour Angle
* measure westerly and only correct for given time.
Celestial equivalent of latitude
Declination north or south of the equinoctal
Polar circles
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
A civil day
360^ rotation in 24 hours
15^ rotation in 1 hour
1^ rotation in 4 mins
Arc to time conversion
Longitude / 15 = Time difference in LT
When converting LMT to LMT
- Longitude West, UTC Best, Longitude East, UTC least
- Always convert through UTC using Date Hour Minute table
- Passing through 180 E/W: from West to East, add one day, from East to West subtract one day
Standard Time
- Is set by each country as stated in Air Almanac and does not necessarily follow 1 hour for each 15^
- May lead to 13 hours difference with UTC
- In Daylight Saving Time in summer, Add one hour to UTC
Moment of Sunrise/Sunset
Top tip of sun rises, 34’ refraction+ 16’ semi diameter = center of sun 50’ below sensible horizon
Civil twilight
6^ below sensible horizon until sunset/sunrise
* varies from 21 mins at equinox at equator to longer at higher latitudes/ summer.
