C15 is a planetary nebula located in the constellation Cygnus. It is commonly referred to as the “blinking planetary”, although many other nebulae can exhibit such “blinking”.
When viewed through a small telescope, the brightness of the central star overwhelms the eye when viewed directly, obscuring the surrounding nebula. However, it can be viewed well in the peripheral vision (averted vision), which causes it to “blink” in and out of view as the observer’s eye wanders.
A distinctive feature of this nebula are the two bright patches on either side, which are known as FLIERs.