The Iris Nebula (also known as NGC 7023 and

Caldwell Caldwell may refer to: People * Caldwell (surname) * Caldwell (given name) * Caldwell First Nation, a federally recognized First Nation in southern Ontario, Canada Places Great Britain * Caldwell, Derbyshire, a hamlet * Caldwell, Ea ...

4) is a bright

reflection nebula In astronomy, reflection nebulae are interstellar cloud, clouds of Cosmic dust, interstellar dust which might reflect the light of a nearby star or stars. The energy from the nearby stars is insufficient to Ionization, ionize the gas of the nebu ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Cepheus Cepheus (Ancient Greek: Κηφεύς ''Kepheús'') may refer to: In Greek mythology * Cepheus (father of Andromeda), and King of Aethiopia * Cepheus (son of Aleus), a king of Tegea, Arcadia In astronomy * Cepheus (constellation), one of the 88 m ...

. The designation NGC 7023 refers to the

open cluster An open cluster is a type of star cluster made of tens to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

within the larger reflection nebula designated LBN 487. The nebula, which shines at magnitude +6.8, is illuminated by a magnitude +7.4 star designated HD 200775. It is located near the Mira-type variable star

T Cephei T Cephei is a Mira variable star in the constellation Cepheus (constellation), Cepheus. Located approximately distant, it varies between magnitudes 5.2 and 11.3 over a period of around 388 days. When it is near its maximum brightness, i ...

, and near the bright magnitude +3.23 variable star

Beta Cephei Beta Cephei (β Cephei, abbreviated Beta Cep, β Cep) is a triple star system of the third magnitude in the constellation of Cepheus. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 690 light-y ...

(Alfirk). It lies 1,300

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s away and is six light-years across.

Notes

References

* *

External links

*
SEDS – NGC 7023

VizieR – NGC 7023

NED – NGC 7023

Dark Atmospheres Photography – Iris Nebula NGC 7023

See NGC 7023 in WorldWide Telescope
{{DEFAULTSORT:Iris Nebula NGC objects 004b Cepheus (constellation) Reflection nebulae Diffuse nebulae