Celestial Objects
Caldwell 15
Nebulae
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Caldwell 15, also known as the Blinking Planetary Nebula or NGC 6826, is a planetary nebula in the constellation Cygnus, discovered by William Herschel in 1793. It lies roughly 2,000 to 3,300 light-years from Earth and takes its popular name from an optical effect in which its faint outer shell seems to appear and disappear as an observer shifts their gaze between direct and averted vision.
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