Small-to-medium sized stars, such as our Sun, form these stunning nebulae at the end of their stellar lifetime when they have exhausted their nuclear fuel.
Life and size
These nebulae survive for 25,000 to 100,000 years, a short life by astronomical standards, and expand at approximately 10 miles (16 kilometres) per second.
The dying stars that eject planetary nebulae – red giants – are not massive enough to become supernovae as they have previously shed some of their mass.
It is estimated that in 5 billion years our Sun will also become a planetary nebulae, following a rapid expansion which will eventually consume the Earth.
Not so planetary
William Herschel incorrectly described these nebulae as “planetary” in 1764 when he mistook the star at the centre for a planet. He later realised his error but kept the name.