NGC 6905 is a superb planetary nebula with the colorful moniker ‘the Blue Flash Nebula’. It’s one of a giant bunch of such nebulae outdoors of the large two, the Ring (M57) and the Dumbbell (M27), vying for prime-time consideration. NGC 6905 is shiny sufficient at magnitude +10.9 to be effectively seen by way of a moderate-aperture telescope with no narrowband filter, and is effectively positioned for observers at mid-northern latitudes on late-summer nights, mendacity within the excessive north-western nook of Delphinus (the Dolphin).
Learn how to observe
In early September, Delphinus is effectively up within the south-southeastern sky by dusk. Neighbouring Sagitta’s well-known ‘arrow’ asterism could be commandeered to assist monitor down the Blue Flash. Look 4 levels east of magnitude +5 eta (η) Sagittae, the star marking the arrow’s tip. You’ll be looking for a compact however irregularly formed nebula spanning simply 47 × 34 arcseconds and nestled inside a triangle of ninth-magnitude stars.
Beneath a typical UK sky, you’ll in all probability want at the very least a 150mm (six-inch) telescope working at a reasonable magnification of, say, 100×. Attempt for it on a moonless night time, which happens in the direction of the top of September. NGC 6905 culminates then at round 9.30pm BST (at round 10.30pm BST in early September) and observing it whereas it’s near its highest elevation is a good suggestion. When you’ve discovered it, strive ramping up the magnification so far as situations will permit and see how a lot distinction an O-III filter makes.
There are conflicting reviews on how vivid NGC 6905’s blue colouring really is, however skilled observers are in a position to discern variations in brightness throughout its face.
