NGC 7293 in Aquarius
September 2026 - Nebula and Cluster of the Month
As autumn nights draw in, the brilliant Milky Way constellations of summer start to drift out of view, leaving what initially appears to be a disappointingly dull set of constellations. Amongst these is the dim sprawl of Aquarius, whose brightest star (β Aqr or Sadalsuud) shines at just magnitude 2.9. Not a huge attention-grabber. Yet Aquarius contains three Messier objects, the fine globular clusters M2 and M72 and the slightly embarrassing M73. There is a third globular cluster, fainter than the Messier objects, NGC 7492. There are also two very noteworthy planetary nebulae, NGC 7009 and the subject of this month’s article – NGC 7293.
NGC 7293 was discovered by the German astronomer Karl Ludwig Harding (1765—1834). The exact date of the discovery is unknown, most probably 1823 or 1824, but it first appeared in a new list of objects compiled by Harding in 1824.
The fact that this large, bright object was overlooked by both William and John Herschel during their great sweeps gives an indication that it is perhaps not as obvious as its magnitude of 7.3 would suggest.
NGC 7293 is a large planetary nebula, measuring about 16’ x 12’, about half the diameter of the full moon. And that’s the problem. The bright magnitude of 7.3 is spread over a large area, making for a low surface brightness. It would not be an exaggeration to say that this object is actually very hard to see. However, all is not lost…
NGC 7293, predictably because of its large angular diameter on the sky, is one of the closest planetary nebulae to us. It is certainly the closest of the conspicuous ones. It lies about 650 light-years (200 pc) from us, making its true diameter about three light-years.
Deep images reveal an unusually high number of knots in the nebula. These are usually interpreted as dense condensations in the progenitor star’s circumstellar material which were subsequently exposed to the ultraviolet radiation and fast wind from the evolving star.1
There has been much research into the interaction between the expanding nebula and the surrounding interstellar medium. A faint bow-shaped feature in the outer halo has been known for some time. In 2013, measurements were made of the Hα velocities from the feature which were consistent with the overall outward velocity of the expanding material 2. The researchers’ interpretation was that the feature represented a bow shock generated as the material expands into and interacts with the surrounding interstellar medium.
Research in 2026 brought a dramatic enhancement of this previous work. Using the partially complete MOTHRA (Modular Optical Telephoto Hyperspectral Robotic Array) telescope, van Dokkum et al 3 discovered 22 compact bow shocks on the eastern outskirts of NGC 7293. Each of these is associated with an individual clump of gas blown off from the star during its AGB phase. The further from the central star they are, the smaller they are, indicating that these expelled lumps of red giant are progressively stripped and disrupted as they travel into the interstellar medium. The estimate is that they will last approximately 10,000 years after expulsion. This gives an unprecedented insight into the galactic recycling of stellar material.
Visually, NGC 7293 can be a problematic object, and this is not helped by its relatively low altitude in British skies. From central Britain, it reaches just 15.7° above the murky horizon.
I first saw it in 1998 through a 10” Newtonian reflector – admittedly from a latitude of just below 42° north. The planetary was at an altitude of 27°, so I may have been cheating a little. I was observing with a friend, and when I had found the object, I called him over. He peered into the eyepiece and grunted. What is it? There’s nothing there.
I handed him my OIII filter and said, Look through this.
Wow! That’s huge!
The point of this is that although initially difficult to see, it is very obvious and bright with a suitable filter, an OIII or UHC. So if you have one of those available, you stand a good chance of seeing it.
As evidence, I include an observation I made in 2015 from southern Scotland (latitude close to 55° north), when the object was 14° above the horizon.
My journal from 1998 (using the 10” (25cm) telescope) reads Enormous! Totally invisible without the OIII filter, unmissable with it in place. A slightly flattened ring with slight gaps at the extremities. A brighter patch is visible in the north-east quadrant.
In 2015, using my 12” (30cm) reflector, I noted Not visible without the OIII filter in place. Huge and dim. Obvious but quite difficult to pin down the elusive details. The outer edge of the ring is almost circular, whilst the inner edge appears more elliptical. There is a distinctly brighter patch in the north-east segment of the ring, and fainter areas at the extremities.
The central star, WD2226-210 shines at magnitude 13.6. This is difficult at low elevations and of course the OIII or UHC filter will make it that much harder to see. I have never seen it.
In my opinion, NGC 7293 is one of the must-sees of the night sky, and September is the time of year to catch it at its best.
| Object | RA | Dec | Type | Magnitude |
|---|---|---|---|---|
| NGC 7293 | 22h 29m 38s | -20° 50’ | Planetary nebula | 7.3 |
Reference:
- Matsuura, M., Speck, A.K., McHunu, B.M., Tanaka, I. & Wright, N.J. (2009). ‘A “Firework” of H₂ Knots in the Planetary Nebula NGC 7293’. The Astrophysical Journal, 700, 395–402.
- Meaburn, J., Boumis, P. & Akras, S. (2013). ‘The bow-shock and high-speed jet in the faint, 40 arcmin diameter outer halo of the evolved Helix planetary nebula (NGC 7293)’. Monthly Notices of the Royal Astronomical Society, 435, 3462–3468.
- van Dokkum, P., Abraham, R., Bowman, W.P., Chen, S., Janssens, S.R., Lokhorst, D.M., Pasha, I. & Rhea, C. (2026). ‘Numerous bow shocks in the outer Helix Nebula’. Nature, published August 2026.
If you'd like to try out the Clear Skies Observing Guides (CSOG), you can download observing guide for the current Cluster of the Month without the need to register. CSOG are not associated with the Webb Deep-Sky Society but the work of Victor van Wulfen.
