NGC 6826
Commonly known as the "Blinking Planetary", a once Sun like star, sits 2,000 light years from Earth in the constellation of Cygnus.
The nebula itself doesn't blink, but as with many planetary nebula, the white dwarf at the centre overwhelms the nebula when viewed by naked eye (in a telescope !), however you can use averted vision by looking just slightly off to the side, and the nebula pops into view. The problem with doing that is, when your eyes naturally try to focus on the thing you're seeing, it vanishes again.
You can try this out yourself without a telescope, simply look up, find an interesting object like the Pleiades and then look just to the side of them, and notice suddenly they become slightly brighter, until you look straight at them again.
This is not common to this nebula, but particularly planetary nebula where the star remnant is far brighter than the nebula illuminated by it.
