With a distance of 700 light years the Helix Nebula in the constellation Aquarius is one of the closest planetary nebula. The outer zone of the nebula was formed by its central star towards the end of its lifetime, roughly 11000 years ago. Today it is possible to see the remains of the star as a bluish white dwarf at the center of the nebula. The strong UV-emission of the star excites the surrounding gas molecules, prompting light emission.
The diameter of the brightest part of the helix nebula is roughly 3.5 light years, which is equivalent to half the diameter of the moon. Additionally, taking into account the outer, less bright zone of the nebula, it has a diameter of 6 light years. For reference, this will appear as almost the same size as the moon in the sky. Parts of the outer zone are already visible in this picture, using a moderate exposure time of 2 hours. The full extent of the outer zone of the nebula is best visible using long exposure times using the light of H-alpha emission.