My 4SA class was taken over by the physics teacher. The students needs more help in Physics than in Math. As for my 5KA class, I continued with the Earth As A Sphere chapter. Lesson was a breeze today compared with the regular days where I have to handle 23 boisterous girls who doesn't know the meaning of quiet. Its sure is a challenge teaching these girls but I enjoy every minute of it. Today we tried some problems on determining the location of places on the earth's surface.
Any location on Earth is described by two numbers--its latitude and its longitude. If a pilot or a ship's captain wants to specify position on a map, these are the "coordinates" they would use. Actually, these are two angles, measured in degrees, "minutes of arc" and "seconds of arc." These are denoted by the symbols ( °, ', " ) e.g. 35° 43' 9" means an angle of 35 degrees, 43 minutes and 9 seconds (do not confuse this with the notation (', ") for feet and inches!). A degree contains 60 minutes of arc and a minute contains 60 seconds of arc--and you may omit the words "of arc" where the context makes it absolutely clear that these are not units of time.
To determine the latitude of a location, imagine that the Earth is a transparent sphere (actually the shape is slightly oval; because of the Earth's rotation, its equator bulges out a little). Through the transparent Earth (drawing) we can see its equatorial plane, and its middle the point is O, the center of the Earth.
To specify the latitude of some point P on the surface, draw the radius OP to that point. Then the elevation angle of that point above the equator is its latitude λ--northern latitude if north of the equator, southern (or negative) latitude if south of it. In the diagram below, the latitude of P is 30°N.
Longitude is distance east or west of a base line called greenwich meridian or prime meridian. The longitude of any given place is its distance, measured in degrees of arc, from this base line.
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