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11-Feb-2004 Just Me and My Shadow
The Rover has Landed! But Where?
The earliest and simplest form of a sundial was called a gnomon. It was simply a stick that was stuck in the ground. Early people would thrust a stick, cut to a standard size (usually about the length of the forearm) in the ground and then measure the shadow length, usually hand-widths. They knew how many hand-widths corresponded to local noon for their area, so they could predict how much of the day was left before sunset. This was critical information, as life got very dangerous after dark, and it was important that travelers find a safe place to rest well before nightfall.
11-Feb-2004 Show Me the Way to Go Home
The Rover has Landed! But Where?
One of the fundamental problems faced by the early explorers was figuring out where they were and which direction they were heading. Magnetic compasses were rare and extremely inaccurate - much too inaccurate to use for long-distance travel (and the Earth's magnetic north pole is not at the geographical north pole anyway!). Travelers quickly realized that during the day the motion of the Sun could tell them which direction was north. Knowing the direction of north allowed them to travel in any direction they needed and still keep up with where they were.
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