Sh2-124 - wonderfuluniverse.de

Sh2-124 from my own „Sterntaucher“ observatory

In 2019, I devoted several clear nights to imaging the beautiful emission nebula Sh2-124 from my backyard observatory. To maximize the efficiency of the available observing time, I employed two identical telescopes mounted side by side, each equipped with a different CCD camera. One system was dedicated to capturing high-resolution H-alpha data, while the second simultaneously recorded the RGB color information. This dual imaging setup significantly reduced the total acquisition time while ensuring that both monochrome and color data were obtained under nearly identical sky conditions. After careful calibration and processing, the H-alpha and RGB datasets were combined to produce a detailed color image highlighting both the intricate gaseous structures and the natural stellar colors.

Sh2-124 lies on the north‑western edge of Cygnus, along the Milky Way, just east of the star pair ρ¹ Cygni and ρ² Cygni. Its centre is around RA 21h 38m–21h 39m and Dec +50° 19′–50° 21′, with galactic coordinates $l \approx 94.5^\circ, b \approx -1.5^\circ$ l≈94.5∘,b≈−1.5∘.

On the sky, the main complex spans roughly 1–1.5 degrees (about 70′×70′), corresponding to a physical size of about 170 light‑years if the commonly adopted distance of 2,600 pc (≈8,500 light‑years) is correct. It is catalogued as an H II region (ionized hydrogen) and also appears as LBN 426 and Avedisova 1220.

Sh2-124 is described in the literature as an “extended and enigmatic” nebular system associated with the infrared source RAFGL 2789, identified with the young stellar object V645 Cygni. V645 Cygni is likely a massive, early‑type star (either an O‑type or a Herbig Ae/Be star) embedded in the nebula and linked to strong infrared and maser emission.

The main ionizing stars are thought to include a blue O7V star and a B2V star, with possible additional hot members in a young cluster that collectively keep the gas ionized. The region shows clear signs of ongoing star formation: multiple infrared sources (including several IRAS objects) and two masers, one in water (H₂O) centred on V645 Cygni and one in methanol (CH₃OH), marking dense star‑forming cores.

The field surrounding Sh2-124 is exceptionally rich in foreground and background stars because the line of sight points almost directly along the plane of our Galaxy. Numerous dark dust clouds are superimposed on the glowing hydrogen, producing striking contrast between bright emission regions and opaque lanes of interstellar dust. These dust clouds absorb visible light and often conceal newly forming stars that can only be studied at infrared wavelengths.

Combining narrowband H-alpha data with broadband RGB images offers significant advantages for astrophotography. While the RGB exposures preserve the natural colors of the stars and reflection components, the H-alpha data dramatically enhances the fine structure and contrast of the ionized gas. During image processing, the H-alpha signal was carefully integrated into the red channel, increasing the visibility of faint nebulosity without compromising the natural appearance of the stellar field. The resulting image reveals subtle wisps of hydrogen extending well beyond the brighter central regions, demonstrating just how extensive these emission clouds are.

Although Sh2-124 is not among the best-known nebulae in the Sharpless catalogue, it represents an excellent example of the faint emission regions that permeate the Milky Way. Imaging such objects requires patience, careful calibration, and many hours of exposure, but the reward is the opportunity to reveal structures that are largely invisible to the human eye. This project also demonstrated the effectiveness of using two synchronized imaging systems simultaneously, allowing both narrowband and broadband data to be collected efficiently and combined into a detailed portrait of one of our Galaxy’s lesser-known stellar nurseries.

Data calibration and registration and the final processing was done with PixInsight. The RGB Data was upscaled to the Hα data. The result was as follows: