Space, Geodesy and Navigation
Many other things can be estimated without an instrument. If an arm is stretched the span of the hand corresponds to an angle of 18 to 20°. The distance of a person, just covered up by the outstretched thumbnail, is about 100 meters. The vertical can be estimated to about 2° and, in the northern hemisphere, observing the Pole Star and using a protractor can give the observer's geographic latitude, up to 1 degree of accuracy.
The Babylonians, Mayans, ancient Egyptians, ancient Indians, and Chinese measured all the basics of their respective time and calendar systems by naked eye:
- the length of a year and a month to ±0.1 hour or to better than 1 minute (0.001%)
- the 24 hours of a day, and the equinoxes
- the periods of the Planets was calculated by Mayan astronomers, to within 5 to 10 minutes accuracy in the case of Venus and Mars.
In a similar manner star occultations by the moon can be observed. By using a digital clock an accuracy of 0.2 second is possible. This represents only 200 meters at the moon's distance of 385,000 km.
Read more about this topic: Naked Eye