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The Bushwalker's Guide to the Galaxy Home Page
Introduction
An Introduction to the Bushwalker's Guide to the Galaxy
Angles
Improvised Angle Measuring Techniques
Reference Directions
Finding Reference Directions from your Surroundings
AlsWorld
by Alan Sheehan B.E.
Measuring Time
Angles can also be used to measure time. As the earth rotates 15 degrees every hour, the height of the sun above the horizon can be used to determine the time since sunrise, or more importantly, the time till sunset. This can be applied to the moon, or any celestial body which is near the celestial equator. Stars away from the equator do not appear to move as quickly, and in fact may not even set, as their motion around the earth is not along a "great circle". For example, a person with a handspan of 15 degrees knows that when the sun is one handspan from the horizon, there is only an hour till sunset. It is worth noting here that, twilight ends about 25 minutes or less after sunset.
This method is at it's most accurate in the tropics, and accuracy decreases with increasing latitude. You have three options:
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accept the inaccuracy, which will always result in a longer time than you have measured;
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correct for your latitude by measuring the angle at 90 degrees minus your latitude from the horizon;
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mathematically correcting for your latitude. For example, at 45 degrees latitude the time will be 1.41 times the estimated time... at 60 degrees latitude it will be 2 times!
Measuring Slopes
Measuring angles is also important for measuring the slope of ground. This can be important to cross country navigators such as bushwalkers, to help confirm positions, or to four wheel drivers to make sure the limitations of their vehicles are not exceeded.
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