Spirograph Nebula

Planetary Nebula IC 418

Apparent magnitude: +9.3
Apparent dimensions: 0.2 arc-minutes
Constellation: Lepus
Image exposure:
5 minutes
Image date:

It’s been a cloudy summer here so far, with plenty of rain and Sydney’s long-term weather forecast still looks something like this:

☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁ ☁

I managed one solitary imaging session a week ago and my targets were two planetary nebulae & the galaxy M77. Unfortunately, the galaxy was ruined by cloud and so this is the last image I’ll be posting until the weather clears up – unless there is a decent evening electrical storm to shoot.

IC 418 is interesting because of its colourful hues, which are unlike my other recently posted planetary nebulae images, most of which have been a cyan appearance. Confusingly, three of my reference books describe IC418 as “greenish-white”; “bright bluish disc”; “a nice reddish oval disc with a bright bluish central star”.

The white blob at the centre of my image could conceivably be the central star but I think it also possible that it could be a bright condensation of gas, over-exposed in my image and masking the star itself. Because of the short exposures (30 x 10 sec), no other star was visible in my image to use in comparison.

The major components of the nebula were described as ionised oxygen and hydrogen. The distance is estimated to be 3,400 light years and the diameter about 0.2 light year.

IC 418 is known as the Spirograph Nebula, because the intricate patterns which can be seen on images taken by the Hubble Space Telescope look similar to the patterns produced by a spirograph. (I wish I had one of those things to play with when I was a kid).

Well, the Webb Telescope has now taken up residence at Lagrange Point 2, 1.5 million kilometres from Earth and we eagerly await the completion of mirror and instrument commissioning, followed by the first images in a few months time.

However, the big news in astronomy this week has been the discovery of a black hole which has no accretion disc or any other object associated with it. You can’t see a black hole on its own, so how on Earth did they discover it?

The astounding answer is that it was passing in front of a background star which was then magnified by the distorted gravitational field of the black hole!

The discoverers refer to this high-magnification microlensing event as: MOA-2011-BLG-191/OGLE-2011-BLG-0462 and it’s in the direction of the Galactic bulge. This exquisite science is reported in their Arxiv paper .

Images © Roger Powell

Telescope:Meade LX-90 200mm Schmidt-Cassegrain
(deforked); 2000 mm f/l @ f/10.
Optics:Astronomik light pollution filter.
Mount & Guiding:SkyWatcher EQ6-R Pro mount.
Imaging camera:ZWO ASI 071 MC cooled.

Cosmic Focus Observatory

34° South

Above us only sky….

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  1. I’ve seen the Spirograph in Hubble images before and always thought it was beautiful. We also had the toy for our kids to play with. You would have enjoyed it.

    I tried my best to follow the pdf of the paper. I got in way over my head. But, I think I understand the basic idea of watching the shift of a distant background star as an invisible massive BH passes in front. I wondered how they knew the BH was there in the first place and to watch for the effects.

    Liked by 1 person

    1. I wouldn’t pretend to read anything much beyond the initial abstract of this paper.
      They probably calculated a microlensing event was a possibility and I’m guessing that they were carrying out a routine data search for strange things going on behind stars in the hope of finding one.

      Liked by 1 person

      1. I went beyond the abstract. Actually read several figure captions. Little of it made sense. Some people in the world are much smarter than I. Glad for it, too.

        Liked by 1 person

  2. “Confusingly, three of my reference books describe IC418 as ‘greenish-white’; ‘bright bluish disc’; ‘a nice reddish oval disc with a bright bluish central star’.”

    This is funny. Did the authors note the colours of their nearby streetlamps?

    Liked by 1 person

    1. I find it amusing to compare different information sources, note the differences and compare them with my own image. Not in any cynical way.

      To be fair, the descriptions were all written by observational astronomers and they can only report what they see with their own eyes. We know that the eye can play tricks when looking through an eyepiece at very faint objects, especially when using averted vision.

      Then of course, imaging may not give the same colour perception as the eyepiece does. The colour rendition from different telescopes using different filter arrangements and varying post-processing techniques can produce different results.

      Regards, 🙃

      Liked by 1 person

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