NGC7023 The Iris Nebula (AlBroxton)

NGC7023 The Iris Nebula

The Iris Nebula, also NGC7023 and Caldwell 4, is a bright reflection nebula and Caldwell object in the constellation Cepheus. 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. Was discovered by William Herschel on October 19th 1794. NGC 7023 was first discovered by Sir William Herschel on October 18, 1794 and since that time it has had a rather confusing catalog history. As usual, Herschel’s notes made the correct assumption of “A star of 7th magnitude. Affected with nebulosity which more than fills the field. It seems to extend to at least a degree all around: (fainter) stars such as 9th or 10th magnitude, of which there are many, are perfectly free from this appearance.” The Iris Nebula (Caldwell 4) is a reflection nebula that lies 1300 light-years from Earth in the Constellation Cepheus. In it we can see a hot newborn star, HD2000775, which has 10 solar masses, emerging from a massive dust cloud. The star's solar winds have cleared a bi-lobed zone surrounding the star that measures 5 x 2.5 light years. The surrounding dust scatters the visible light from the star, just as our atmosphere scatters sunlight in the sky, rendering the nebula sky blue. In some filaments just above the star, the dust is converting invisible ultraviolet light into visible red light by photoluminesence. The blue nebula is surrounded by dark obscuring clouds of dust. While the Iris nebula is often referred to as NGC 7023, this is not strictly correct. NGC 7023 refers to the associated open star cluster to the west. The correct designation for the nebula itself is LBN 487.

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Allen Broxton

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