The Helix Nebula: an enormous and handsome planetary!


The Helix Nebula (NGC 7293) is a large however low-surface-brightness planetary nebula. Photos can reveal placing element across the interior fringe of the nebula’s essential envelope and fainter outer areas. Picture: Kfir Simon.

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. Trying like a large, vibrant celestial smoke-ring, the Helix can show considerably difficult although at all times irresistible for visible observers.

The Helix Nebula lies in southern Aquarius, north-west of first-magnitude Fomalhaut (alpha [a] Piscis Austrini and south-east of magnitude +3.3 Skat (delta [d] Aquarii. AN graphic by Greg Smye-Rumsby.

Tips on how to 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 night time, so attempt to observe it when it very near or on the southern meridian.

Its rapid environs are noticeably missing in vivid stars to signpost the best way, however you should utilize lowly (declination –29 levels) however vivid Fomalhaut (magnitude +1.17, alpha [α] Piscis Austrini) in case you can see it (you’ll have to safe an excellent southern outlook in any case to see the Helix). Upsilon (υ) Aquarii (magnitude +5.2), which is positioned about 10 levels (roughly the width throughout your knuckles held out at arm’s size) north-west of Fomalhaut, is handily positioned simply over a level east of the Helix Nebula. 

If Fomalhaut is just not seen otherwise you’re undecided you’ve recognized it appropriately, try an alternate 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 extra 2.8 levels on is the aforementioned upsilon.

On a high quality, moonless night time at a website free from main gentle air pollution, the Helix, which shines with a catalogued magnitude of +7.5, needs to 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 not less than 14’, half the obvious diameter of the total Moon, afflicting the Helix with a continual low floor brightness that makes a little bit of a mockery of its comparatively bright-sounding magnitude – its gentle 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 greater 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, gained’t be seen, nevertheless it radiates considerably within the blue-green gentle of doubly-ionised oxygen (O-III). The Helix’s magnitude +13.5 central star needs to be seen in such an aperture.

A large-field, bi-colour view of the Helix Nebula. Picture: Martin Pugh.

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