The remnant of a star in the constellation of Aquarius that has cast off its outer layers to form an approximately spherical shroud of nebulous material, a planetary nebula. Since its formation approximately 10,000 years ago, the nebula has expanded to fill a volume of space nearly six light years from side to side. As viewed from Earth, the nebula gives the impression of a somewhat helical structure, hence its common name of the Helix Nebula. Two lobes extend out in opposite directions from the round central formation, creating a shape strongly reminiscent of an eye (and so the nebula is sometimes informally known as the 'Eye of God' or the 'Eye of Sauron').
Within the nebulous material, a system of thousands of cometary knots appear. These are dense clumps of material within the nebula, from which 'tails' of material can be seen streaming away from the nebula's core. These features were first discovered within the Helix Nebula, but have now been observed in a large number of similar planetary nebulae.
The Helix is one of the closest planetary nebulae to the Solar System, close enough that its distance can be calculated through the measurement of its parallax. Early estimates placed it as far as eight hundred light years from the Sun, but the more recent Gaia data suggests that it is rather closer than this. Based on that more precise data, the distance to the Helix Nebula is now thought to be something close to 655 light years.