Nebulae in Cepheus and Cassiopeia

20 – 21 September 2020, 21:45 – 01:00

Conditions: Chilly, breezy. Light condensation appearing as the temperature dropped.

Seeing: Good
Transparency: Poor

With Mars now larger than the magic 20-arcsecond threshold, deep-sky observing (and indeed deep-sky astrophotography) will be playing second fiddle to the red planet for the next couple of months. (The autumn constellations will be back next year; Mars won’t be this good again until 2030-something.) That said, the nights are getting longer, so I was able to get a couple of hours of observing before Mars took centre stage.

I started with a short wander around Cygnus at 133x, during which I stumbled across 27 Cyg – a close double in a dark nebula (B146). The transparency in this part of the sky was very poor (the Crescent Nebula was disappointing – even with the filter it was barely visible ), so I relocated to Cepheus.


NGC 7538, emission nebula, Cepheus

133x + OIII filter. Initial impression was of an amorphous patch of light, like a puff of smoke, surrounding a pair of 11th magnitude stars. Averted vision showed some detail in the form of mottling, including what looked like a dark lane or rift on the eastern side of the nebula. Not a showpiece object by any means, but not bad given the middling conditions. Switching up to 171x plus the Ultrablock filter gave much the same view, but larger and fainter – although the two central stars were easier to see. The nebula was just barely visible without the filters.

IC 1470, emission nebula, Cepheus

133x + OIII filter. I never know quite what to expect when tracking down obscure IC-designated nebulae. Sometimes they’re surprisingly bright; other times they’re all but invisible. However this object was fairly easy to spot as a quite small, fuzzy round patch of light. The core appeared stellar with averted vision. Increasing the magnification to 171x (no filter) showed a star embedded in a wide, fan-shaped nebula, a bit like a comet. (It reminded me of Hubble’s Variable Nebula, NGC 2261.) The Ultrablock filter offered a little improvement: the central star became harder to see, while the nebula itself seemed more triangular and harder-edged.

A quick look at the eye-catching clusters NGC 7510 and Mrk 50 (see last year's notes on these) and then onto another nebula.

NGC 7635, Bubble Nebula (Caldwell 11), Cassiopeia

171x + Ultrablock gave the best view, though it wasn’t nearly as good as my previous look at this object (perhaps the Ethos plus the OIII filter would be a better combination). Bright star associated with a nebula of indistinct shape; with averted vision it looked a little bit like one half of a Yin-Yang symbol.

NGC 40, “Bow-Tie Nebula” (Caldwell 2), planetary nebula, Cepheus

171x + Ultrablock filter. While reading up on this nebula (after my observation on 16 September), I found some reports claiming it responds better to narrowband filters than OIII. Now I’ve tried both I do think the Ultrablock filter gives a slightly better view than the OIII, but this nebula is bright enough that it doesn’t really need it. The two arcs were a little easier to see (with averted vision), but of course it helps when you already know where they are.


Mars: The combination of the 9mm Nagler and the 2.5x Powermate (giving a magnification of 333x) seemed to hit the sweet spot tonight, giving me my finest view yet. The SPC was a brilliant little oval and the Sinus Meridiani (home of the Mars Opportunity rover) and Sinus Sabaeus regions were showing particularly well. I could also see a blue haze over the north polar region and brighter patches along the morning limb. I swapped the eyepiece for a camera and captured some videos, resulting in the image below: