The Helix Nebula (NGC 7293 and Caldwell 63) is arguably Aquarius’ showpiece deep-sky vacation spot. As one of many largest and most remarkably structured of all planetary nebulae, it’s one of many must-see however trickier to picture objects of the autumn sky. Wanting like an enormous, vibrant celestial smoke-ring, the Helix can show considerably difficult although all the time irresistible for visible observers.
How one can observe
The Helix Nebula has a declination of –20 levels, which locations it within the extra southerly reaches of Aquarius. Sadly, it by no means achieves an altitude of 20 levels from UK shores, culminating at round 18 levels from the south of England at about 11pm BST on the finish of September. It’s important to reap the benefits of each diploma of altitude to get the very best view of the Helix on any given evening, so attempt to observe it when it very near or on the southern meridian.
Its fast environs are noticeably missing in vibrant stars to signpost the way in which, however you should utilize lowly (declination –29 levels) however vibrant Fomalhaut (magnitude +1.17, alpha [α] Piscis Austrini) should you can see it (you’ll must safe a very good southern outlook in any case to see the Helix). Upsilon (υ) Aquarii (magnitude +5.2), which is situated about 10 levels (roughly the width throughout your knuckles held out at arm’s size) north-west of Fomalhaut, is handily situated simply over a level east of the Helix Nebula.
If Fomalhaut will not be seen otherwise you’re undecided you’ve recognized it appropriately, try another route ranging from the higher-lying star Skat (magnitude +3.2, delta [δ] Aquarii). Shifting south-westwards, look out for magnitude +4.7 66 Aquarii some 4 levels away after which an additional 2.8 levels on is the aforementioned upsilon.
On a nice, moonless evening at a web site free from main mild air pollution, the Helix, which shines with a catalogued magnitude of +7.5, must be snared by way of an 80–100mm (~three- to four-inch) telescope working on the lowest magnification and, ideally, with an O-III or UHC filter. Its symmetrical ‘eye’, or oval-shaped type, extends to at the least 14’, half the obvious diameter of the total Moon, afflicting the Helix with a persistent low floor brightness that makes a little bit of a mockery of its comparatively bright-sounding magnitude – its mild being unfold over a big space of sky!
Observers utilizing telescopes within the 200mm (eight-inch) class, in all probability observing from extra southern climes the place the Helix lies increased within the sky, have reported seeing a blue-green hue. The Helix’s reddish hue, from the sunshine of hydrogen-alpha which dominates within the overwhelming majority of pictures, received’t be seen, but it surely radiates considerably within the blue-green mild of doubly-ionised oxygen (O-III). The Helix’s magnitude +13.5 central star must be seen in such an aperture.
