IC 1805
IC 1805 · Heart Nebula — stellar winds, dust and star formation in stages
This field shows the Heart Nebula not as an isolated red silhouette but as part of the larger W3/W4 complex in the Perseus arm. At the center lies the cavity of W4, cleared out by young massive stars; along its edges stand dense dust clouds, bright ionization fronts and small pillars. At the lower right of the image sits IC 1795, already part of the neighboring W3 region. What looks like one continuous nebular landscape therefore contains several physically distinguishable stages.
Three names for three layers. IC 1805, or Melotte 15, strictly denotes the young open cluster at the center. The optically glowing hydrogen region is cataloged as Sh2-190, the larger radio source complex as W4. In astrophotography, “IC 1805” usually means the whole heart-shaped gas field. The difference is more than nomenclature: the small cluster supplies a large share of the ionizing ultraviolet radiation, while gas and dust show how that energy acts on its surroundings.
A field several hundred light-years across. Depending on the method, the literature places the complex at roughly 2.0 to 2.4 kpc. On the deliberately conservative 2.0 kpc scale, the astrometrically solved field of 3.346 × 2.231° measures about 381 × 254 light-years. At 2.4 kpc it would be some 458 × 305. The distances within the image are therefore not small gaps between individual clouds but structures on the scale of entire stellar associations.
Melotte 15 shapes the central bubble. The cluster is only a few million years old. Among its most energetic members are HD 15570, HD 15629 and the spectroscopic binary HD 15558. Their ultraviolet light ionizes hydrogen; stellar winds and earlier massive stars clear out the interior and compress material at the edges. Particularly bright arcs need not be denser “walls” in a geometric sense: a curved shell also appears brighter where the line of sight runs tangentially through more glowing gas.
Dark does not mean empty. The gray central zones are partly a genuinely gas-poor bubble interior. The sharply bounded black tongues, by contrast, consist of dust and molecular material in front of the glowing background. At BRC 5 one can even follow how such a cloud is compressed and photo-evaporated by radiation coming from the direction of Melotte 15. Fukuda et al. found 17 Hα-emitting young stars there and were able to reproduce the asymmetric shape through radiation-driven implosion of a cloud originally of about 400 solar masses. That is strong local evidence for triggered star formation, but no proof that every young star in W3/W4 arose the same way.
IC 1795 is a neighbor, not the interior of the heart. The compact fish head at the lower right belongs to the W3 side of the complex. Work on the W3/W4 system assigns IC 1795 to a younger stage of hierarchical star formation: large-scale feedback first shaped the molecular cloud; later IC 1795 and W4 acted on still younger embedded regions. The image shows this spatial neighborhood but cannot, on its own, prove the temporal causality.
Two star clusters feign depth. Stock 7 and NGC 1027 lie in front of the nebula only in projection. Gaia-based work places Stock 7 at roughly 0.68 kpc and NGC 1027 at about 1.14 kpc; W4 stands considerably farther back. NGC 1027 is moreover some 130 million years old, Melotte 15 only a few million. In the photograph they share the same red backdrop; in space and in time they do not belong together.
What the color means. Salmon red is Hα, cyan O III — the two windows of the dual-band filter. Positions, shapes and relative structures are reliable; the exact line ratio of any given pixel is not.
Where in the sky
The rectangle is this image's real field of view, with its measured rotation — not a symbol. Constellation figures and star positions come from SIMBAD.
2 entries sit within 24° of each other here — click a field to jump to it.
Crops
IC 1795 · Fishhead
IC 1795 · Fishhead Nebula — the compact W3 neighbor region
49.4′ × 37.6′·02h 26m 05.03s +62° 05′ 17.6″
Field of view 49.4′ × 37.6′, at 2.0 kpc roughly 94 × 71 light-years. The bright complex, threaded by dark dust lanes, is IC 1795, known in astrophotography as the Fishhead Nebula. It belongs to the W3 side of the W3/W4 complex and is not merely a bright knot inside the central W4 bubble.
The sharply drawn dark contours arise from foreground dust in front of ionized gas; the bright cavity marks the surroundings of the young star cluster IC 1795. CO and star-formation studies link this region to the dense boundary layer between W3 and W4. Oey et al. place IC 1795 in a temporal sequence in which large-scale feedback shaped older cloud structures and IC 1795 later acted on the still younger embedded W3 regions. The photograph shows the morphology of this interaction, not its chronology directly.
Melotte 15 · bubble engine
Melotte 15 · the cluster in the cleared-out center of W4
52.9′ × 40.8′·02h 33m 34.11s +61° 30′ 52.3″
Field of view 52.9′ × 40.8′, at 2.0 kpc roughly 100 × 77 light-years. Near the lower center lies Melotte 15, the few-million-year-old star cluster at the center of IC 1805. The overlay additionally marks HD 15558; together with HD 15570 and HD 15629, that system is among the most energetic stars of the cluster.
The diffuse, comparatively empty zone to the right of the cluster is part of the cleared-out bubble interior. At the upper left, denser dust tongues cut into the emission; at the right, a bright curved front bounds the field. The crop thus shows cause and effect in one image: concentrated young stars, a thinned-out cavity, and compressed or ionized rim structures. The exact three-dimensional position of individual arcs nevertheless cannot be determined from the projection alone.
W4 · the wide field
W4 in context · heart bubble, dust fronts and IC 1795 at the edge
1.95° × 1.52°·02h 33m 11.66s +61° 11′ 26.4″
Field of view 116.7′ × 91.3′, at 2.0 kpc roughly 222 × 173 light-years. This crop contains nearly the whole classic heart shape. Melotte 15 lies near the center; the bright outer arcs trace the compressed H II shell, dark lanes lie in front of it as dust and molecular gas. BRC 5 stands southeast of the center, Stock 7 projects in front of the southwestern rim, and IC 1795 already appears in the lower right corner.
It is precisely the large scale that shows why the heart is neither a simple ring nor a closed sphere. Density differences, burst shells, absorption and the viewing direction shape the silhouette together. To the north, W4 continues far beyond the optically familiar heart; to the right, the neighboring W3 region begins at the same time. The overlays therefore separate cluster, cloud core and adjacent H II region from one another instead of calling every bright structure IC 1805 wholesale.
Dust wall & Stock 7
Dust front at the southwestern rim · Stock 7 in front of it only in projection
30.2′ × 31.1′·02h 31m 30.67s +60° 26′ 11.8″
Field of view 30.2′ × 31.1′. At the W4 distance that would correspond to roughly 57 × 59 light-years; at Stock 7's distance of about 0.68 kpc, to only some 19 × 20 light-years. These two scales genuinely do belong on top of one another: the loose star cluster Stock 7 / Markarian 6 lies in the foreground near the lower edge of the image, while the extended red emission and the dark cloud structures behind it belong to the line of sight toward W4.
The visual focus is the rugged dust front. Small black islands and one long dark body absorb the Hα-rich background light; on the right side the transition to the ionized region grows brighter. From the two-dimensional image, not every dark structure can be assigned unambiguously to a single cataloged cloud. What is certain, by contrast, is the depth ordering: Stock 7 is not the cluster that blew up the Heart Nebula.
BRC 5 · cloud under pressure
BRC 5 · an irradiated cloud head at the edge of the Heart Nebula
35.0′ × 26.2′·02h 28m 07.57s +61° 21′ 08.6″
Field of view 35.1′ × 26.2′, at 2.0 kpc roughly 67 × 50 light-years. The dark cloud head tapering upward is BRC 5, or SFO 5. The overlay sits at the published position of the embedded IR/submillimeter core IRAS 02252+6120; it does not mark the brightest optical pixel. The side of the cloud facing the cluster is ionized and photo-evaporated by the ultraviolet radiation from W4.
Fukuda et al. found 17 Hα-emitting young stars around BRC 5, among them objects near the cloud surface and one toward the IRAS core. Their simulation reproduced the asymmetric shape through radiation-driven implosion of an originally elongated cloud of about 400 solar masses. The crop is thus a good local candidate for feedback-triggered star formation — with the important qualification that the study does not trace every young star in the entire W4 complex to the same mechanism.
NGC 1027 & northeastern front
NGC 1027 and the northeastern front · a foreground cluster over a young W4 rim
1.05° × 0.74°·02h 39m 17.98s +61° 36′ 36.3″
Field of view 63.3′ × 44.3′, at 2.0 kpc roughly 120 × 84 light-years. At the upper edge lies NGC 1027. Tripathi et al. identify 217 probable Gaia members, a distance of about 1.14 kpc and an age of some 130 million years. The cluster therefore stands far in front of W4 and is dozens of times older than Melotte 15; the red nebular backdrop is only a projection behind it.
A bright ionization front along the northeastern rim of W4 runs diagonally across the field. On it, the second overlay marks 2MASS J02394268+6200458, the Class I YSO source 36 from Panwar et al.'s study of pillar-like structures in the W4 complex. The crop thus combines two entirely different populations: an old foreground cluster and a very young object on an irradiated cloud front several thousand light-years farther away.
Acquisition and processing
Taken on the night of August 23/24, 2026 in Friedrichsdorf with a ZWO ASI2600MC Air on a William Optics RedCat 71 (349 mm focal length) and a dual-band filter, gain 100, sensor temperature in the range −10.0 to −9.8 °C. The full WBPP run submitted 47 lights and integrated 46 individual exposures of 120 s each, that is 92 min, into the main master. It is precisely this main master that forms the data basis of the manually finalized gallery source selected here.
WBPP calibrated with a master dark generated from twelve temperature-matched 120 s raw darks as well as the current master flat and master bias. LocalNormalization remained active; the main integration used PSF signal weighting. One light failed registration and entered neither the main master nor any downstream products.
In the linear image the green excess was first reduced multiplicatively and the large-scale background then corrected with DBE. BlurXTerminator ran correctively on the linear image, NoiseXTerminator once for linear noise reduction. Processing continued starless and with a separate star layer; stretch, color balance, local contrast and the controlled HDR reduction were then tuned manually and finished in Photoshop. The web source is a 10-bit AVIF in Display P3 with an HDR gain map; the SDR and HDR variants come from the same source.
The new gallery source was measured astrometrically in its own right: 7,533 reference stars, residual error 0.91″, scale 2.2205″/pixel, image center 02h 33m 04.00s +61° 30′ 10.2″. The field measures 3.346 × 2.231°, the sensor angle is 87.0° — north therefore lies almost to the right in the image. Crop sizes, sky coordinates and overlays are computed from exactly this solution, not estimated from the preview.