Heart Nebula (IC 1805)


Heart Nebula – Nov 2021

The Heart Nebula in the constellation of Cassiopeia is a large region of ionised hydrogen gas. The centre of the nebula contains a small cluster of new stars which are responsible for ionising the surrounding gas clouds. The radiation from these bright stars are also pushing back the gas clouds, giving the nebula its distinctive heart shape. Another named feature of the nebula is the Fish Head nebula (IC1795) which is the bright region to the left of the main nebula in the above image. The nebula is located about 7500 light years away and although classed as lying within Cassiopeia it lies outside the familiar W asterism of this constellation, in the direction of Perseus. 

The image above is the first time I have combined H-Alpha data with a colour image. The advantage of introducing H-alpha data is that it has a very high level of contrast to the background sky – with an H-alpha filter, light pollution and even moonlight in the background sky glow is filtered out, leaving only the H-alpha signal from the nebula against a dark sky. Another advantage of an H-alpha filter is that useful data can be gathered even under a full moon, increasing the number of nights available for imaging. The H-alpha data in this image was in fact taken under a full moon, then the colour data was gathered about a week later before moonrise.

To create the image, both sets of data are stacked separately, but using a common star reference image. The H-alpha data was then mixed with the red channel of the colour data and fed back into the colour image, then the H-alpha data was also used as a luminance layer to add more detail into the nebula. This luminance layer is applied at about 25% opacity, otherwise the colours become a pale pink colour, but this low opacity is still sufficient to enhance the detail. Some care has to be taken with star colour in this process, so the stars were separated out for separate processing.      

Image Details

  • Date: H-Alpha – 21st Nov 2021, RGB – 28th Nov 2021
  • Exposure Details: H-alpha – 32 x 1000s (8hrs 53min), F6, ISO400. RGB – 37 x 400s (4hrs 7min), F6, ISO400
  • Total Integration Time: 13hrs
  • Camera: Canon EOS100D (modified)
  • Telescope: Altair Astro 72EDF at 432mm focal length.
  • Mount: Skywatcher HEQ5
  • Guide Scope: Altair Astro 60mm
  • Guide Camera: QHY5LII
  • Filters: H-alpha – Baader 7nm H-alpha 2 inch Filter. RGB – Astronomik CLS Clip-In Filter

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