Chapter 1 : Introduction Flashcards
What type of orbit does earth revolve around the sun?
Elliptical Orbit
Orbital path and orbital speed of earth governed by -
Kepler’s Laws
Angle at which Earth’s axis is inclined to Orbital Plane?
66 1/2 degrees [23 1/2 degrees to the Normal to the Orbital Plane]
Inclination of the Earth’s Axis the cause of -
- Seasons
- Changing time interval between Sunrise and Sunset throughout the year
Actual Shape of Earth?
Oblate Spheroid
Flattening of Earth at poles called -
Compression
QB: Earth Compression -
0.03 % {1/300th]
QB: Which is more? Earth Polar Diameter or Earth Equatorial Diameter?
Earth Equatorial Diameter; Greater by 50 km
Datum used to define Direction?
Direction in which Earth spinning - East
Therefore, Sun rises from East
QB: What is a Great Circle?
Circle on the Surface of Earth whose - Centre and Radius is that of Earth itself.
The shortest distance between 2 points on Earth is - Shorter arc of the Great Circle joining the 2 points.
Shortest Distance between 2 points on Earth?
Shorter arc of the Great Circle joining the 2 points.
How many Great Circles can pass through 2 points on the earth?
One.
Unless points diametrically opposite.
What is a Meridian?
Semi Great Circle joining North and South Poles
QB: What direction do Meridians indicate?
True North - South direction
QB: Meridians cross equator at?
90 degrees
What is the Prime (Greenwich) Meridian?
- Meridian passing through Greenwich
- Datum for measuring Longitude
What is the Equator?
- Great Circle whose plane is at 90 degrees to axis of rotation of earth.
- Datum for measuring Latitude
What is a Small Circle?
Circle on the surface of the earth whose center and radius is NOT that of the earth.
Smalls circles of relevance - Parallels of Latitude
QB: What are Parallels of Latitude?
Small circles on the surface of the earth whose planes are parallel to the plane of the Equator. Lay in East-West direction.
Function - Indicate position North and South of Equator.
What is a Graticule?
Network formed on map or surface of globe by -
- Prime meridian, Meridians, Equator, Parallels of Latitude
Using Graticule, “Angular Measurements” used to define position of point on the Earth’s surface.
What is the fundamental unit of Angular measurement?
Degree
What is a Degree?
Angle subtended at the center of a circle, by an arc, equal to “360th” part of the Circumference.
Degree divided by - 60 minutes of arc
Minute divided by - 60 seconds of arc
What are Latitude and Longitude?
Angular Measurements used to define position on earth in a Spherical System
QB: How is latitude of a position measured? / What is latitude?
Latitude of any point - is the arc measured along the meridian through the point - from Equator to the point
Annotated N or S depending on whether point N or S of equator
What is Geocentric Latitude?
Smaller angle between - Line from point on sfc. of earth joining to center of the earth - and - the Plane of the Equator
What is Geodetic Latitude?
Smaller angle between - Normal to the point on the merdian on the spheroid - and - the Plane of the Equator (Normal normally doesn’t pass through the center of the spheroid)
Where does the maximum difference between Geocentric and Geodetic Latitude occur?
45 degrees N or S (11.6 minutes of an arc)
What are the special Parallels of Latitude?
Arctic Circle - 66 1/2 N
Tropic of Cancer - 23 1/2 N
Tropic of Capricorn - 23 1/2 S
Antarctic Circle - 66 1/2 S
QB: How is longitude of a position measured? / What is longitude?
Longitude of any point - is the arc measured along the equator - from Prime Meridian to Meridian through the point.
Annotated E or W depending on whether point is E or W of the Prime Meridian
QB: What is C.Lat / D.Lat?
Angular difference between 2 Latitude angles
Direction of C.Lat / D.Lat - Depends on from which point you are moving.
QB: What is C.Long / D.Long?
Angular difference between 2 Longitude angles
Direction of C.Long / D.Long - Depends on point from which you are moving
QB: What is Convergency?
Meridians converge towards the poles.
Convergency is the angle of inclination between 2 given meridians measured at a stated latitude.
Difference between G.C. direction of G.C., measured at each meridian.
QB: Where does Maximum and Minimum Convergency occur?
Maximum - At poles
Minimum - At equator (0 degrees at equator)
What is the main effect of Convergency?
Since meridians define direction with reference to True North - And since Meridians converge - The direction of a Great Circle constantly changes.
Thumb rule for Great Circle direction -
G.C. is -
Concave to equator
Convex to poles
Change in direction of Great Circle in the N.H. -
In the N. H. - [Concave to Equator]
Direction of Easterly G.C. - Increases
Direction of Westerly G.C - Decreases
Change in direction of Great Circle in the S.H. -
In the S. H. - [Concave to Equator]
Direction of Easterly G.C. - Decreases
Direction of Westerly G.C - Increases
What is a Rhumb line?
It is a line of constant direction. It is a curved line drawn on the surface of the earth which cuts ll meridians at the same angle.
Rhumbs lines used to be used to by ships to navigate along.
What are the no. of Rhumb lines drawn between 2 points?
One
What are the common Rhumb lines?
- Parallels of Latitude
- Equator (Also a G.C.)
- Meridians (Cut Angle is 0 degrees***)(Also a G.C.)
Thumb rule for Rhumb line direction -
R.L. is -
Convex to equator
Concave to poles
Comparision bet. G.C. and R.L. bet. two points 1 -
Which is closer and farther from equator -
R.L. nearer to equator
G.C. farther from equator
Comparision bet. G.C. and R.L. bet. two points 2 -
Length and Direction
Distance - G.C. is shorter distance.
Comparision bet. G.C. and R.L. bet. two points 3 -
When Points on Meridian and Anti-Meridian
G.C. via pole (Changing direction at pole)
R.L. along Parallel of Latitude
Comparision bet. G.C. and R.L. bet. two points 4 -
When Points on Equator
Line joining points is G.C. and a R.L. (constant direction)
1 cm = ? mm
10 mm
1 mt = ? cm = ? mm
100 cm = 1000 mm
1 mt = ? feet
3.28 feet
I feet = ? inches
12 inches
1 inch = ? cm
2.54 cm
1 yard = ? feet
3 feet
1 km = ? mt
1000 mt
1 km = ? feet
3280 feet
- Avg. distance between Equator and Pole in km
- Avg circumference of Earth in km
10000 km
40000 km
1 sm = ? mt = ? km
1600 mt = 1.6 km
1 sm = ? feet
5280 feet
1 nm = ? mt = ? km
1852 mt = 1.852 km
1nm = ? feet
6080 feet
What is a nautical mile?
It is the length of the arc of a G.C. which subtends an angle of 1 minute at the center of the Earth.
Therefore - Nautical mile directly related to Angular Measurements of Lat. / Long.
1 nm = 1 minute of Latitude
1 nm = ? minute of latitude
1 minute
1 degree of Latitude = ? nm
60 nm
1 nm at Equator = ? minute of longitude
1 minute
QB: Derive Avg. between Equator and Poles in nm
Hence, Derive Circumference of Earth in nm
Degree change between Equator and Pole = 90 degrees
1 degree = 60 nm
Therefore, Avg. between Equator and Poles in nm = 90 degrees in nm = 90 X 60 = 5400 nm
Hence, Circumference of Earth = 5400 X 4 = 21600 nm
QB: Length of nm in feet at Pole, at Equator due to Compression
Avg. Value of nm in feet
Nautical Mile at Pole = 6100 feet
Nautical Mile at Equator = 6050 feet
Avg. Value of nm in feet = 6080 feet
Calculation of G.C. distances (Not to remember) -
- Points on Same meridian, Same Hemisphere
- Points on Same meridian, Diff. Hemisphere
- Points on Meridian & Anti - Meridian (Same Hemisphere)
- Points on Meridian & Anti - Meridian (Diff. Hemisphere)
- Anti-Podal Points
What Northern and Southern Vertices of Great Circle?
G.C. distance between them?
Northern Vertix - Most Northern point of a G.C.
Southern Vertix - Most Southern point of a G.C.
G.C. bet. them - 10800 nm.
Any Meridian Line is a -
Rhumb line and Semi - Great Circle
