Naked eye
Freiäugig or freisichtig those observations and measurements in science and technology called that are obtained without optical aid (other than corrections of refractive errors ), ie. , Without using, for example, telescope, magnifying glass, microscope or camera
The term is mainly used in astronomy, geodesy, physics and biology, and circumscribed with other words such as " naked eye ", " naked eye ", " right " or " without magnification visible". The everyday language uses the term rare because almost all daily activities take place freiäugig and this goes without saying. Only in more demanding tasks, such as recognizing the finest details, with accurate measurements or unusual lighting conditions is the power limit of the eye closer attention.
Interesting phenomena
Even with free ( naked ) eye to interesting phenomena and interesting phenomena can be observed, but also the accessibility of amazing accuracy. Here are some examples:
Estimation of geometric parameters
- Symmetries can be estimated accuracy of about 1 to 2 percent if one assumes a favorable position and some experience has
- Intervals over a short distance better than 10 %, on white paper accurately even at 3 to 5%, and details on the map about 0.2 mm
- Straightness of a meter rod to about 0.5 mm, a straight border line to about 1 cm per 50 m ( see also alignement)
- Usual distances and speeds: With Clue to a few percent, with no clue to 10 to 20 %
- Brightness, hue: similar to above ( about 3 to 20%), see also Weber- Fechner law
Visibility of fine details
- Resolving power: 0.01 to 0.02, depending on the contrast ° or an average of 3 cm at 100 m, based on double stars about 200 "
- Detectability of thin lines: with good contrast resolution of about 5-10%, ie 1-3 mm at 100 m (simple self- test, for example with wire fence)
- Brightness differences at 2-5 % ( when compared directly ), or about 10 %
Astronomical phenomena
- About 2000 stars ( in a big city a few hundred ). The faintest stars 6 size is about 1012 times weaker than sunlight - ie the eye can differences in brightness of 1: Process 1 trillion
- Some double stars, planets 6 ( under extremely favorable conditions, Uranus, with a transit of Venus and the "sliver " of Venus) and color differences on the brighter stars
- Some star clusters (even if the individual stars were invisible ) and fog (eg Pleiades, Orion, Andromeda and Triangulum Galaxy. latter is 2.8 million light- years distant freisichtige the object)
- The Milky Way (the single star under the limit of visibility remain ) and average one comet per year
- Dozens of shooting stars per night, although they have only the size of dust grains
- Freiäugige astrometry: angle estimate to be about 1 ° (eg, Polaris, latitude or direction of a ship's course)
- Seasons, or the length of the year: possible in a lifetime to about 1 hour, over the course of several centuries of cultural history to a few minutes
- Periods of the planets: the Mayas succeeded eg for Venus, Mars and Moon on 5-10 minutes exactly
- Occultations of stars by the Moon on tenths of a second - which are only 100-300 m in 385,000 km distance.
Observations in biology
- Visibility of fine structures: for example, to sensors of insects up to 0.01 mm
- Size and color differences
- Movement patterns, flight characteristics
- Determine the vertical ( plumb ) to 1-2 °
- Unconscious recognition of movements (warning reflex)
- Estimation of speeds to 5-10 percent