The Helix Nebula is one of the most famous deep sky objects and the nearest bright nebula to our solar system. It is a large planetary nebula located approximately 695 light years from Earth in the direction of Aquarius constellation. Its striking appearance earned it the nickname the Eye of God.
The nebula is relatively close to the solar system and appears as almost one-half the Moon’s diameter.
It is a popular object for amateur astronomers and can be observed with binoculars – it appears as a hazy, greenish cloud.
The ring shape can only be resolved with large amateur telescopes, and the nebula’s radial streaks cannot be seen except through the largest ground-based telescopes.
The Helix Nebula was created at the end of the life of a star similar to the Sun, when the star evolved into a red giant and shed its outer layers.
The star’s outer gasses, expelled into space, are lit by the remnant central core of the star, which will become a white dwarf when it cools down.
NGC 7293 was the first planetary nebula discovered to have cometary knots, which many planetary nebulae were later discovered to contain.
Each of these knots contains bright cusps and tails, and they all extend away from the central star in a radial direction. Most of the knots are believed to be roughly the size of the solar system.
The nebula is believed to contain about 20,000 cometary knots.
The Helix Nebula is also interesting because it appears really similar across a wide spectrum, from ultraviolet to infrared, and is easy to recognize at all these wavelengths even though there are noticeable differences in the nebula’s appearance.
The Helix Nebula spans about 2.87 light years.
Its official designation in the New General Catalogue is NGC 7293.
The nebula’s inner disk is 8×19 arcminutes in diameter, the outer torus has a diameter of 12×22 minutes of arc, and the outermost ring is roughly 25 arcminutes in diameter.
The nebula was discovered by the German astronomer Karl Ludwig Harding in the early 19th century.
It has an apparent visual magnitude of 7.6 and expands at the rate of 31 kilometres per second.
The nebula’s inner disk expands at a rate of 32 kilometres per second, and the outer ring’s expansion rate is estimated at 40 kilometres per second.
The nebula’s age is estimated to be around 10,600 years.
Helix Nebula – NGC 7293
Coordinates: 22h29m38.55s (right ascension), -20°50’13.6” (declination)
Apparent dimensions: 25’
Radius: 2.87 light years
Apparent magnitude: +7.6
Absolute magnitude: 6.58
Designations: NGC 7293, Caldwell 63
Planetary nebulae and their shapes explained:
Zoom into the Helix Nebula, seen in infrared: