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This is because directions are observed along great circles (circles which divide the earth into two hemispheres), not along circles of latitude. If I cut the earth using knife cuts that are due North, South, East, and West of me, it will divide the earth into 4 equal quarters, much like quartering an apple.
a) The set of all points which are due east of me is a great circle which is tangent to the circle of latitude. It crosses the equator in the Republic of The Congo, at longitude 20 degrees east (90 degrees and 6 hours before Boston). It continues on until it ends on the other side of the world, in the Indian Ocean, south west of Australia. This is real, not perception. If a telephone pole could be erected in the Republic of the Congo, tall enough to be seen over my horizon, I would observe it as due east. If it were 93 million miles tall, then the sun would physically pass through it when I saw the sunrise on the equinox. It guess this means that the Congo's telephone pole would need to be taller than 93 million miles for me to notice.
a) The set of all points which are east-north-east of me is a great circle which passes through Canada and Europe and crosses the Tropic of Cancer in Saudia Arabia, at longitude 42.5 degrees east (112.5 degrees and 7.5 hours before Boston). I see the sun north of true east at my sunrise, when it is directly over Saudia Arabia. |
