NGC 6826 (also known as Caldwell 15 ) is called the “Blinking Planetary” as it blinks due to the nature of the human eye. When you look at it directly your cone cells in the center of your retina sees a star, but when you use averted vision your rod cells see the nebulosity around the star, which disappears. This is an effect that cannot be photographed, it has to be seen visually with your eye at the eyepiece of your telescope.
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