Navigation Flashcards
What shape is the Earth?
An oblate spheroid - not round although we assume it is
N.B. Flattened at the poles and bulges slightly at the equator due to rotation of the Earth
Define Great circle
A circle drawn on the surface of the Earth whose radius and centre are the same as the Earths
N.B. Examples are the equator and all lines of longitude. Great circles are the shortest route
Define Small Circle
A circle drawn on the surface of the Earth whose radius and centre are not the same as the Earth’s
N.B. Examples are all lines of latitude apart from the equator
Define Equator
A great circle whose plane is perpendicular to the Earth’s axis of rotation and which divides the Earth into two equal hemispheres
Define Meridian
A semi-great circle joining the poles. Lines of longitude (including prime meridian at 0º)
N.B. Geographic/True North and South poles
Define Rhumb Line
A regularly curved line on the surface of the Earth that cuts all meridians at the same angle
What are the names of the cardinal points?
- North - 000º/360º
- East - 090º
- South - 180º
- West - 270º
What are the names of the quadrantal points on a compass?
- NE - 045º
- SE - 135º
- SW - 225º
- NW - 315º
Distances along a great circle
1 minute = __________
60 minutes = __________
- 1nm
- 1 degree
Define Nautical Mile
The distance on the surface of the Earth along a Great Circle which subtends an angle of 1 minute of arc measured at the centre of the Earth
N.B. See Form of the Earth slides for examples in calculating the distance along the arc of a great circle
What is the circumference of the Earth?
21,600nm
N.B. Earth is 360º, 1 minute = 1nm, 1 degree = 60 minutes therefore 60nm, therefore 60 minutes x 360 degrees = 21,600nm
Define Kilometer
Generally accepted as one 10,000th of the average distance between the equator and either pole
What is a Foot (ft)
A unit of measurement that has no relationship with any Earth dimension. (Probably originated from Roman times) Used for vertical navigation
1ft = 0.3408m or 30.48cm
Conversions
- 1 nautical mile = __________km
- 1 nautical mile =__________ft (Mile high)
- 1 statute mile = __________ft
- 1 kilometre = __________ft
- 1 nautical mile = 1.852km
- 1 nautical mile =6080ft (Mile high)
- 1 statute mile = 5280ft
- 1 kilometre = 3280ft
Conversion Factors
- Feet to metres
- Metres to feet
- Nautical miles to kilometres
- Kilometres to nautical miles
- Nautical miles to statute miles
- Feet to metres = Feet x 0.3048
- Metres to feet = Metres x 3.2808
- Nautical miles to kilometres = Nautical miles x 1.852
- Kilometres to nautical miles = Kilometres x 0.5396
- Nautical miles to statute miles Nautical miles x 1.15
Comparisons
- 41 nautical miles ~ __________ km
- 41 statute miles ~ __________ km
- 41 nautical miles ~ __________ statute miles
- 41 statute miles ~ __________ nautical miles
- 41 nautical miles ~ 76 km
- 41 statute miles ~ 66 km
- 41 nautical miles ~ 47 statute miles
- 41 statute miles ~ 35.5 nautical miles
Which way does the Earth rotate?
Eastward or anti clockwise if viewed from above the North Pole
What is the tilt of the Earth?
23.5º
What causes seasons?
The Earths 23.5º tilt means that there is a resultant global heating differential throughout the year as the Earth moves around the sun. This creates seasons
At any point on the Earths surface, when the Sun reaches the highest point in the sky during any given day, the time is __________
Noon
N.B. Length of the day according to solar time is not the same throughout the year because apparent motion of the sun varies
Define Night
The hours between the end of evening civil twilight and the beginning of morning civil twilight
Define Civil Twilight
Civil twilight ends in the evening when the centre of the sun’s disc is 6º below the horizon and begins in the morning when the centre of the sun’s disc is 6º below the horizon
What is mean solar time and what sort of time is mean sun used to measure?
Based on the motion of an imaginary sun travelling at an even rate throughout the year
Used to measure:
- Coordinated Universal Time (UTC)
- Time Zone
- Local Time
What is UTC?
Coordinated Universal Time
- It assumes that the sun crosses the Greenwich Meridian at 1200 and uses a 24 hour clock