At the heart of this expansive four-panel mosaic lies the Iris Nebula, also cataloged as NGC 7023 or Caldwell 4, glowing with a vivid blue light produced by reflected starlight. This reflection nebula is illuminated primarily by the hot, young star HD 200775, whose radiation scatters off fine interstellar dust grains, giving the Iris its characteristic blue hue. Embedded within the nebula is the sparse open cluster OCL 235, whose stars are still closely linked to the dusty molecular environment from which they formed.

Surrounding the Iris Nebula is an intricate web of faint interstellar dust clouds, often referred to as galactic cirrus. These wispy structures trace cold, diffuse material within the Milky Way and are visible here through a combination of reflected starlight and subtle extinction against the dense star field. With over 81 hours of total integration, this mosaic reveals both the bright core of NGC 7023 and the delicate, large-scale dust flows that connect it to the surrounding interstellar medium, highlighting the complex interplay between stars, dust, and light.

Image Description and Details :

The Iris Nebula is a reflection nebula in the constellation Cepheus, which is actually a patch of interstellar dust illuminated by a blue star. In the 2-panel-mosaic wide-field image, you can see that this area of the sky is actually filled with interstellar dust, but the other dust is not illuminated by nearby stars like the Iris Nebula. Image Telescope/Lens: SharpStar 150 2.8 HNTImage Camera: QHYCCD QHY268CMount: iOptron CEM 70Frames :301 * 300sIntegration: 25.1 hoursLocation: Milky Way Observatory, Kangbao County, Zhangjiakou, Hebei Province, China.

Copyright Information: Steed Yu

The Iris Nebula (also known as NGC 7023 and Caldwell 4) is a bright reflection nebula and Caldwell object in the constellation Cepheus. Reflection nebulae are clouds of interstellar dust which might reflect the light of a nearby star or stars. The energy from the nearby stars is insufficient to ionize the gas of the nebula to create an emission nebula, but is enough to give sufficient scattering to make the dust visible. Thus, the frequency spectrum shown by reflection nebulae is similar to that of the illuminating stars. Among the microscopic particles responsible for the scattering are carbon compounds (e. g. diamond dust) and compounds of other elements such as iron and nickel. The latter two are often aligned with the galactic magnetic field and cause the scattered light to be slightly polarized.