Iris Nebula in Cepheus

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.

NGC 7023 is actually the cluster within the nebula, LBN 487, and the nebula is lit by a magnitude +7 star, SAO 19158.

It shines at magnitude +6.8. It is located near the Mira-type variable star T Cephei, and near the bright magnitude +3.23 variable star Beta Cephei (Alphirk). It lies 1,300 light-years away and is six light-years across.

NGC7023, Iris Nebula in Cepheus. Immagine ottenuta da Champorcher (Valle d'Aosta) con un Takahashi FS102 a f/6, Moravian G2 8300 e filtri LRGB Baader. L 26x600", RGB 4x600" per ciascun canale.

Copyright: Piermario Gualdoni