Averted vision is a technique for viewing faint objects which involves not looking directly at the object, but looking a little off to the side, while continuing to concentrate on the object. This technique is very useful to astronomers, as it often allows them to see especially faint or otherwise invisible objects. By developing the technique, some observers report a gain of up to three or four magnitudes. The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value There is some evidence that the technique has been known since ancient times, as it seems to have been reported by Aristotle while observing the star cluster now known as M41. Aristotle (Greek Aristotélēs) (384 BC – 322 BC was a Greek philosopher a student of Plato and teacher of Alexander the Great. Messier 41 (also known as M 41 or NGC 2287) is an Open cluster in the Canis Major constellation.

A similar technique that employs the same principle is called scope rocking, and is done by simply moving the telescope back and forth slightly to move the object around in the field of view.

Physiology

In the simplest sense, averted vision works because there are no rods (cells which detect dim light in black and white) in the fovea: a small area in the center of the eye. Rod cells, or rods, are Photoreceptor cells in the Retina of the Eye that can function in less intense Light than can the other type The fovea, also known as the fovea centralis, is a part of the Eye, located in the center of the Macula region of the Retina. The fovea contains only cone cells, which serve as bright light and color detectors and are not as useful during the night. Cone cells, or cones, are Photoreceptor cells in the Retina of the Eye which function best in relatively bright Light. The density of the rod cells usually reaches a maximum around 20 degrees off the center of vision. However, due to the way the cells are connected to the nervous system, the most sensitive portion of the eye is usually 8 to 16 degrees away from the center. This is because photoreceptor cells closer to the center have more ganglion cells connecting to them, and thus more nerve connections. A ganglion cell (more correctly a retinal ganglion cell or RGC) is a type of Neuron typically located near the inner surface of the Retina

It is also important to note that it also matters whether you avert right or left. The most effective direction is that which places the object on the nasal side of the vision. So, for right-eyed observers it is best to shift to the right, and for left-eye observers it is best to shift to the left. Some people also claim that it is better to avert up instead of down. The best thing to do is practice and find the best location for one's own eyes.

See also

• Peripheral vision
• Scotopic vision
• Purkinje effect

External links and references

• "Just What is Averted Vision, Anyway?"
• Techniques for Good Observing
• M41 possibly recorded by Aristotle

Peripheral vision is a part of vision that occurs outside the very center of gaze Scotopic vision is the Monochromatic vision of the Eye in low light The Purkinje effect (sometimes called the Purkinje shift, or dark adaptation and named after the Czech Anatomist Jan Evangelista Purkyně

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