|Visual Observation of M42 - Orion Nebula|
Sketch by Jeremy Perez, Flagstaff, AZ.
It boils down to biology, in particular how your eye works. Your eye has a light sensitive area called the retina which is composed of two types of light-detecting cells called rods and cones. The difference..?
- Cones, located near the center of the eye, are capable of detecting color when there is plenty of light available. They are not so good, however, at detecting low light levels such as through a typical amateur telescope.
- Rods, on the other hand, are much more sensitive to low light levels. They do not, however, detect color and are located mostly away from the center of the retina - this is why you can often detect more detail when viewing an object through a telescope by using "adverted vision", effectively looking not directly at the object but slightly off center so that you bring your rods into play.
CCD Image of M42 - Orion Nebula
Mike Petrasko & Muir Evenden - Insight Observatory