Heart Nebula – 28th 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. The image was originally processed in Photoshop, but I have revisited the editing using Pixinsight.
To create the image, both sets of data were stacked separately, but using a common star reference image. The colour image was then split into separate RGB channels, then the channels were re-combined back to full colour, but this time using the more detailed H-alpha data in the red channel. The H-alpha filter removes a lot of the red colour from starlight, therefore after re-combination the stars had a very turquoise colour cast. Therefore the stars were removed and replaced with the original RGB stars. The overall result is an image with increased detail and contrast in the red nebula, but with correctly balanced star colours.
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