Milky Way in Cassiopeia and Cepheus

On this page a 24°×35° wide-field view of the Milky Way in constellations Cassiopeia, Cepheus and the north-eastern part of Cygnus is presented in different color composites. This region is full of smaller emission nebulae. For many of them the ionization sources an thus the distance can be determined which provides an insight in the 3D structure of the milky way in that direction.

All pictures below are downscaled versions. Full resolution images with more than 100 megapixels can be loaded with a Javascript viewer by clicking on the images in the first section. Selected details are shown in the second section. The third section contains a presentation of some discoveries. Image and instrument data can be found at the end of this page.

Full views

Click on the images to load a full resolution version with up to more than 100 megapixels using a JavaScript viewer.

Milky Way in Cassiopeia and Cepheus in H-alpha, blue continuum and red continuum
This image is a false color composite where H-alpha (including red continuum) is mapped to red, blue continuum (including [OIII] and H-beta emissions) is mapped to green and red continuum (without H-alpha) is mapped to blue. Reflection nebulae appear green to blue, HII regions are red. Stars in the continuum channels are partially subtracted in order to make the faint nebulae visible.

Milky Way in Cassiopeia and Cepheus in H-alpha
Legend for false color image of Milky Way in Cassiopeia and Cepheus in H-alpha
This visualization is a pseudo color image which only uses the H-alpha data (including some red continuum). It shows much more details of the emission nebulae than the image above.
Color composition: After partial star subtraction the dynamic range was compressed using a non-linear hi-pass filter. That leads to a compression ratio r which is used to calculate the color as depicted in the legend. (The legend shows the compression c:=1-r). Blue regions least compressed while white regions are most compressed. The luminance is determined by the tonal curve corrected result of the dynamic range compression.

Milky Way in Cassiopeia and Cepheus in RGB
An almost-true color image. Unlike to the other images the stars are not subtracted. This improves the visibility of dark nebulae that absorb the light from the stars behind.
Due to limited resolution of continuum channels the image is only presented at half resolution.

Selected details

Here are a few details that also can be seen using the JavaScript viewer.

SH2-131 (containing the Elephant Trunk Nebula and SH2-129 in H-alpha and continuum
The upper large nebula is SH2-131. It contains the famous globule called the "Elephant Trunk Nebula" and is ionized by the star cluster IC 1396 in the center. The distance of this cluster is about 3000 light years and it lies on the periphery ot the Cepheus Bubble, also see the observations section.

The lower large nebula is SH2-129 and is ionized by the bright star near the center. According to recent estimations its distance is about 2300 light years, see ([2]).

SH2-171 ans SH2-170
The larger nebula is Sh2-171. It is ionized by a star cluster in the center which lies in a distance of about 3500 light years. The smaller bright nebula on the left side is SH2-170, also see this larger view.

Observations and discoveries

The constellations Cassiopeia and Cepheus are full of small emission nebulae. For many of them the ionization sources are known. This allows distance measurements using latest Gaia data and thus provides an insight in the 3D structure of the Milky Way in that direction.

The objects for which distances are known are divided into three groups. The following list contains a brief description and links to presentations for each group.

The views above shows many nebulae that cannot be found in catalogs. (The JavaScript Viewer makes it easy identify objects using catalogs or SIMBAD and to define new objects.) Some (probably not all) of these unexplored nebulae have been collected in the list below. Click on the following links for a presentation. Notes

Image data

Images where captured with a camera array which is described on the instruments page.

Image data are:

Projection type: Stereographic
Center position: RA: 22h48, DEC: 59°
Above: North is right
JavaScript viewer: North is up
Scale: 10 arcsec/pixel (in center at maximum resolution)
FOV: 34°×24° (RA×DEC, through center)
Exposure times: Sum of exposure times of all frames used to calculate the image.
H-alpha: 9.2 d
Continuum channels: 6.1 d

Image processing

All image processing steps are deterministic, i.e. there was no manual retouching or any other kind of non-reproducible adjustment. The software which was used can be downloaded here.

Image processing steps where:

  1. Bias correction, dark current subtraction, flatfield correction
  2. Alignment and brightness calibration using stars from reference image
  3. Stacking with masking unlikely values and background correction
  4. Star subtraction
  5. Denoising and deconvolution both components (stars and residual)
  6. RGB-composition (same factor for stars and residual for the true color composite)
  7. Dynamic range compression using non-linear high-pass filter
  8. Tonal curve correction


  1. Cepheus bubble as seen by the AKARI satellite in far infrared (50µm to 180µm)
  2. Szilágyi, Máté & Kun, Mária & Ábrahá, Péter & Marton, Gábor. (2023). "The Gaia view of the Cepheus OB2 association". Monthly Notices of the Royal Astronomical Society. stad027.
  3. Romano L. M. Corradi & Nicolas Grosso & Agnès Acker & Robert Greimel & Patrick Guillout. (2014). "Gas physical conditions and kinematics of the giant outflow Ou4". Astronomy and Astrophysics. 570. A105.

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