NGC 7023 (Cepheus)
Fig. 1 - A flower in the dust: The bright reflection nebula NGC 7023 (Caldwell 4) in Cepheus, photographed with a 16-inch f/4.5 Dob on an equatorial platform.
| Object name: | Constellation: | Coordinates: | Apparent size: | Visual brightness: |
|---|---|---|---|---|
| NGC 7023 (LBN 487) | Cepheus | 21h02m / +68°10' | 18' x 18' | 6.8 mag |
The bright reflection nebula NGC 7023 (LBN 487, Caldwell 4, "Iris nebula" - for its resemblance to an iris flower) in the constellation Cepheus. NGC 7023 is an object of some confusion, as pointed out in Deep-Sky companions: The Caldwell Objects by James O'Meara: Some sources identify it as an open star cluster, others as a nebula. The discoverer of NGC 7023, William Herschel, clearly described the object as "a large nebulosity around a 7th-magnitude star" and also mentioned the existence of many stars associated with the nebulosity, but he didn't indicate a star cluster.
John Louis Emil Dreyer described NGC 7023 as an extremely or excessively large nebulosity in his famous NGC catalogue from 1888 (thus NGC 7023 clearly is a nebula). The confusion probably occured when Swedish astronomer Per Collinder erroneously listed NGC 7023 as a star cluster in his Collinder Catalogue published in 1931, also calling it Collinder 429.
The dominant color of the brighter part of the reflection nebula NGC 7023 is blue, characteristic of dust grains reflecting starlight: The nebula is lit by a 7 mag bright star, SAO 19158. The Iris nebula is about 1,300 light-years from Earth and measures six light-years across. NGC 7023 was discovered by William Herschel in 1794 (source: Wikipedia).
Exposure time: 2h 18min (46x approx. 3min) at ISO 800, taken on September 15/16 and October 13, 2018. Processing with DeepSkyStacker and Photoshop. No calibration frames were taken.
Equipment: Canon EOS 450D Baader modified camera, TeleVue Universal Paracorr coma corrector, 16" f/4.5 "Ninja" dobsonian telescope riding on a dual-axis Tom Osypowski equatorial platform, Lacerta MGEN autoguider, Lacerta off axis system.
Field of view comparison: image of the moon with the same setup.
Fig. 2 - Search chart for NGC 7023. The map erroneously identifies it as an open star cluster. Copyright 2025 'The Mag-7 Star Atlas Project', www.siaris.net.