IC 1805
IC 1805 (Sharpless 190)
Heart of the Heart Nebula
Emission Nebula in Cassiopeia

Click here for higher-resolution versions:  40% (1612x1602)  65% (2620x2604) 100% (4031x4006)
Click on image to cycle through the six versions of the image (described below and labeled on the lower left corner of each image)


IC1805, also known as Sharpless 190, is a large emission nebula, in which star-forming is taking place. The emission nebula is predominantly red, because (i) ionized hydrogen emits in the red part of the spectrum; (ii) the vast majority of the light matter in the universe is hydrogen, and (iii) the hydrogen near the new stars is being ionized (stripped of its electron) by the highly-energetic young stars being formed in the star cluster (predominately those at the upper left of the image; the star cluster is called Melotte 15).

This image is a "close-up" of the central part of the much larger nebula. I imaged this 16 years earlier, with a smaller telescope (and chip); you can see in that larger field of view why the entire nebula is called the "Heart Nebula." Click here to see the older version.

This nebula is about 7500 light years from Earth and is roughly 200 light years across; the portion shown in this photo is about 70 light years across. Visually, it is about the same width as a full moon.

I have presented this object in six different formats (each image is labeled in the lower left corner), each a fairly common way to process this kind of data-set; I very much like each one in its own way. This is the order in which they appear as you cycle through (by repeatedly clicking on the photo, waiting for each to download):

(i) A true-color version (LRGBNB, the top photo in the stack), with the color created by imaging through red, green and blue filters (with a significant amount of Ha and OIII data blended into various channels, in varying percentages; Ha emissions are in the red spectrum, and OIII emissions are blue-green, so I have blended Ha into the luminance layer and the red channel, and OIII into the green and blue channels).

(ii) A bi-color version (HOO, almost true-color version; the second photo in the stack), in which "red" is ionized hydrogen emissions (Ha), and the green and blue channels both are doubly-ionized oxygen emissions (OIII), which are blue-green in color. It's a fair substitute for having red, green and blue channels, but, because the green and blue channels are the same, the star colors are a bit wonky. I used the Ha master as the luminance (detail) layer. It's interesting to me how close this came to the much more complex (with much more data) true-color version above, but with some less color breadth. Yes, it lacks the depth and punch of the full color with narrowband version, but it only uses a fraction of the data (so much quicker to complete gathering data), and those who image from heavily light-polluted areas can have more success with narrow band imaging than with broadband imaging.

(iii) A true-color version, without using any narrow band data (LRGB, all color is derived from data collected through red, green and blue filters, and the luminance layer does not contain any Ha component), as a comparison to the result when loaded with NB data. The more I gaze at this version, the more I like it (especially the vibrant colors).

(iv) A version in the Hubble palette (SHOtan, a lot of the Hubble photos, including and especially the famous "Pillars of Creation," are made with this set of filters, since it's a useful set for scientists to see what's actually happening), which shows SII emissions as red, Ha emissions as green, and OIII emissions as blue. The luminance layer is the Ha master. Because the green from the dominant Ha emissions can make this look odd, people often "neutralize" the green, turning it into a tan. I have done that with this image (the next image has some green left in it), as well as increasing the contribution of the OIII (blue) and SII (red) data. Consider that everything red in the first three images would be green in this one if I had not largely ignored the Ha data; the yellow/brown parts of this one show sulfur emissions, and the blue show oxygen emissions.

(v) A version in the Hubble palette (SHOgreen), which shows SII emissions as red, Ha emissions as green, and OIII emissions as blue (with the Ha emissions amost completely de-emphasized in this rendition because they would be so dominant otherwise, with the entire nabula just being green). I used the Ha master as the luminance layer. Consider that everything red in the first three images would be green in this one if I had not largely ignored the Ha data; the yellow/brown parts of this one show sulfur emissions, and the blue show oxygen emissions.

(vi) A pure Ha version (grayscale, showing only light in the very narrow Ha band); this is fun for me to gaze at in full resolution, to see all the detail in the structure.

These are the most frequent ways images of emission nebulae are likely to be presented, so I thought it would be fun to include all of them, to be able to compare and contrast the different presentations. The "true color" version which includes narrow-band data is, to me, the most beautiful of the lot (generally speaking, I prefer "true-color" to false color), so I put it at the top; the narrow-band data adds contrast and detail to the image, and makes the stars smaller, which is pleasing to me, while maintaining the "true color" nature of the data. The Hubble palette versions are also very pretty (especially the tan version, IMO), and it's nice to include the (relatively sparse) sulfur emissions that I spent a bunch of hours gathering. The grayscale Ha image is, to me, striking in its smoothness (and the gray, of course, is the color you see when you look at this through a telescope).


Technical Information:

Ha:OIII:SII:L:R:G:B: 660:360:240:660:180:240:240 (a total of 43 hours of light-frame exposure time used in this photo); luminance, red and green exposures were all 15-minute exposures; blue all 20-minute exposures; Ha, SII and OIII were all 30-minute exposures.

Equipment: RC Optical Systems 14.5 inch Ritchey-Chretien carbon fiber truss telescope, with ion-milled optics and RCOS field flattener, at about f/9, and an SBIG STX-16803 camera with internal filter wheel (SBIG filter set), guided by an SBIG AO-X, all riding on a Bisque Paramount ME German Equatorial Mount.

Image Acquisition/Camera Control: Maxim DL, controlled with ACP Expert/Scheduler, working in concert with TheSky X.

Processing: All images calibrated (darks, bias and sky flats), aligned, combined and cropped in Pixinsight. Color combine in Pixinsight. Some finish work (background neutralization, color calibration, deconvolution and noise reduction both done with Russ Croman's marvelous tools) done in Pixinsight; some cleanup finish work was done in Photoshop CC.

Location: Data acquired remotely from Sierra Remote Observatories, Auberry, California, USA.

Date: Images taken on many nights from December 2022 through April 2023. Image posted August 20, 2023

Date: Image scale of full-resolution image: 0.56 arcseconds per pixel.

Seeing: Generally very good, with individual calibrated luminance frames varying from 1.6 to 2.2 arcsecond FWHM.

CCD Chip temperature: -25C

Copyright 2022, 2023 Mark de Regt

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