The Helix Nebula, also known as NGC 7293, is a large planetary nebula in the constellation of Aquarius. It is perhaps the nearest planetary nebula to our Solar System. The popular name Helix Nebula refers to the nebula's appearance on photographs. The Helix has been referred to as the "Eye of God" on the Internet, since about 2003.
Overlooked by previous astronomers, notably Frederick William Herschel, this nebula was discovered by Karl Ludwig Harding some time before 1824.
NGC 7293 is one of the largest planetaries known: it covers an area 16' in diameter, more than half of that of the full moon; it halo extends even further to 28'. Although the nebula is quite bright, at magnitude 7.3, its light is spread over this large area so it has extremely low surface brightness. It is not an easy object for visual observing. (This is perhaps why the Herschels never observed it.) Its ring structure, so conspicuous in photos, is not easy to detect visually.
In binoculars and rich field scopes, the planetary is a large ghostly disk, vaguely circular, with a much fainter center. In larger instruments it is very challenging, so use a very low power eyepiece. An O-III or UHC filter and averted vision can help quite substantially. Three 10th magnitude stars are involved in the disk.
The Helix Nebula is the closest of all planetary nebulae, lying at a distance of about 650 light years. The nebula spans an area 2.5 light years across. Currently, NGC 7293 is estimated to be 10,600 years old, based on a measured expansion rate of 31 km/sec.
The Helix Nebula is shaped like a prolate spheroid, with strong density concentrations along its equatorial plane. The outermost ring is flattened on one side due to its collision with the interstellar medium.
The Helix Nebula was the first planetary nebula discovered to contain knots. These knots are radially symmetric, and are described as "cometary", containing bright cusps and tails. There are estimated to be more than 20,000 cometary knots in the Helix; excluding their tails, they are approximately the size of the Solar System.