NGC 225 The Sailboat Cluster & van den Bergh 4

The image presents two fascinating main objects, NGC 225 and van den Bergh 4 (vdB 4), both located in the northern constellation Cassiopeia.

NGC 225, also known under the catalogue designation Collinder 7 and sometimes referred to as the Sailboat Cluster, was discovered in 1783 by William Herschel. It is an open cluster situated roughly 2200 light-years away. The cluster is noteworthy for an apparent pattern that, according to many sources, strongly resembles a sailboat – a resemblance that, I must admit, is not immediately obvious to me. The age of NGC 225 is estimated at around 100 million years, which places its stars in comparatively early stages of their evolution relative to typical main-sequence stellar lifespans.

Van den Bergh 4, catalogued by Sidney van den Bergh in the 1960s, contrasts with the star cluster as it is a faint reflection nebula illuminated by nearby stars. Its light is not intrinsic: dust particles within the nebula scatter starlight, preferentially reflecting blue wavelengths and giving vdB 4 its delicate, diffuse bluish appearance. Although the exact distance to vdB 4 remains uncertain, it is generally considered to lie in the vicinity of NGC 225 when viewed from Earth.

Within the field covered by the image, several additional dark and bright nebulae can also be identified, including LDN 1291, LDN 1302, and LBN 604, which contribute further structure and interest to this region of Cassiopeia.

Image Acquisition

This image combines data from both of my telescopes: the Takahashi TOA-150 and the Takahashi FSQ-106N.

Originally planned as a pure broadband RGB project to capture the region's natural colours, I later added hydrogen-alpha (Ha) exposures for enhanced detail. 

For the TOA-150, I used Astrodon filters for the Ha-RGB set, while the FSQ-106N was paired with Baader RGB filters. The image data from both instruments were later registered and combined, allowing the strengths of each optical system—resolution and field coverage—to contribute to the final result.

The total integration time amounts to 44 hours.

Image Processing

After calibration and registration, the workflow produced three separate datasets: Ha from the TOA-150, RGB from the TOA-150, and RGB from the FSQ-106N.

The processing sequence was as follows:

Extraction of the luminance layer from the TOA RGB data, ensuring maximum preservation of fine detail.

Combination of the TOA RGB and FSQ RGB datasets to create an improved, more robust colour image.

Enhancement of the colour image with the Ha data, followed by colour recalibration using the SPCC tool.

Enhancement of the luminance image with the Ha data to strengthen faint structures.

Delinearisation of both the luminance and colour images, followed by reinsertion of the luminance into the colour image to produce the final result.

Click on the images for full resolution versions, or go to the Gallery section for complete exposure details.

Image processing: Pixinsight.

Observatory automation and remote operation with  Talon6.