Very good Cygnus (the Swan) owns the summer season nights. It’s a constellation overloaded with vibrant deep-sky objects, together with some distinctive nebulae. In Cygnus’ deep-sky hierarchy, the Crescent Nebula (NGC 6888, Caldwell 27, SH2-105), a fantastically intricate, bubble-like Wolf-Rayet nebula, can declare to lie within the high rank, though it may possibly present a little bit of a stiff problem for visible observers.
It’s a dream of an object for deep-sky imagers although, with the fierce stellar wind from the huge Wolf-Rayet star (WR 136) on the nebula’s centre sculpting its complicated filamentary construction because it barrels into copious quantities slower-moving gasoline already thrown-off by the star whereas in its purple large section.
Learn how to observe
Cygnus can seem like a complicated and disorientating place for the uninitiated. The deep-sky beginner and not using a GoTo mount, sweeping throughout its wealthy Milky Manner star fields can quickly get misplaced. Fortunately, the Crescent isn’t too troublesome to seek out when you’ve recognised the general form of the ‘Northern Cross’, Cygnus’ major asterism or star sample.
Mighty Deneb (alpha [a] Cygni), one of many fabled ‘Summer season Traingle’ stars, marks the tail of the Swan, whereas Sadr (gamma [g] Cygni), mendacity simply over six levels south-west of Deneb, lies on the intersection of the Cross. If you happen to preserve transferring in the identical course away from Sadr, after 2.7 levels you’ll land on NGC 6888. There’s a small triangle of seventh-magnitude stars mendacity simply to the east. In late-August, the Crescent Nebula culminates nearly on the zenith at about 11pm BST.
On a advantageous and moonless night time a 150mm (six-inch) telescope, working at round a magnification 100x, may have ample mild grasp to point out the brightest a part of this elliptical-shaped nebula, a few seven-arcminute-long and one-arcminute-wide arc on its north-eastern facet that’s oriented north-west to south-east (place angle 215 levels). You’ll fare higher although with a 200–250mm (eight to 10 inch) aperture telescope. Total, the Crescent covers 20 x 10 arcminutes and lies 4,700 mild years away, giving it a bodily diameter of 25 mild years.
One important accent for observing the nebula is an O-III or UHC narrowband filter, which can enhance the distinction between the Crescent and the sky background; successfully, the nebula will ‘pop’ into view.