Caldwell 15 – The Blinking Nebula (NGC 6826)

NGC 6826 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. This bright, planetary nebula lies southwest of an 8.5 magnitude star. Stare at the planetary’s magnitude 10.6 central star through a medium or high power eyepiece until its brightness overwhelms the eye (saturates the cones of the eye) and causes the nebula to fade. When you then glance away and look at the nearby magnitude 8.5 star, the planetary’s disk will reappear. It is an apparent “blink” only.

This alteration between direct and averted vision of the planetary’s nucleus thus causes the nebula to blink. NGC 6826 was discovered by William Herschel on Sep 6, 1793. It’s number 15 in the Caldwell catalog.

I thought the best way to demonstrate and capture this saturation effect was to offer two exposures: the first at 4” and 12,800 ISO and the second at 8” and 51,600 ISO. They are presented above. See the difference? One shows a sky blue disk with a bright white dwarf and the other exhibits red, white, and blue in a partially blinked disk.

The reason it appears like this was is that I purposely OVEREXPOSED THE CAMERA so that it might super saturate the detector elements similar to how the eye might do it (Do not worry, the camera is undamaged). It worked!

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