Retina nebula

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Retina nebula
Observational Data
Designation IC 4406
Right ascension 14h 22m 26.21s[1]
Declination -44° 09′ 02.0″[1]
Constellation Lupus
Type of object Planetary nebula
Dimensions 100" x 30"[2]
Distance from Earth 3,500 ly[3]
Radial velocity -22±5 km/s[1]

The Retina nebula (IC 4406) is a planetary nebula in the southern constellation of Lupus.[3] The nebula possess an unusually rectangular structure with a white dwarf star at its centre. The nebula is uncommon as it has dust lanes that can be seen to weave their way across the nebula. These dust lanes are incredibly intricate and the nebula's name arises from a comparison of these dust lanes to the retina of the eye.[4]

Properties and Structure

The Retina nebula is a bipolar planetary nebula meaning it consists of two enormous lobes diametrically opposed to each other, forming a shape very similar to a hollow cylinder.[5] We see the curved face of the cylinder resulting in the nebula's rectangular appearance. It is thought if we were able to view the nebula from the top, it would appear circular like other planetary nebulae such as the Ring nebula or the Owl nebula. The precise distance the nebula is rather uncertain with estimates ranging from 2,000-5,000 light years.[3] This means it's apparent size of 100 arcminutes long corresponds to a physical size of 0.97-2.4 light years.[6]

There are a large number of dark dust lanes that cross the nebula and these are thought to be approximately 160 AU across.[4] Various elements, including helium, oxygen, nitrogen, neon and argon, have been found in the nebula with a roughly uniform concentration along the nebula.[7] The nebula is believed to also possess a relatively dense torus at its equator like many other planetary nebulae.[8] At the centre of the nebula is a white dwarf that is thought to have a temperature of some 80,000 kelvin.[2]


  1. 1.0 1.1 1.2 IC 4406 from the [ SIMBAD Astronomical Database]
  2. 2.0 2.1 Smith, C., Zijlstra, A. and Fuller, G. (2015). A molecular line survey of a sample of AGB stars and planetary nebulae. Monthly Notices of the Royal Astronomical Society, 454(1), pp.177-200. arXiv:1508.05014
  3. 3.0 3.1 3.2 The Boxy Retina Nebula from
  4. 4.0 4.1 The Retina Nebula, a bipolar planetary nebula in Lupus from
  5. IC 4406: A Seemingly Square Nebula from
  6. By direct calculation using the given apparent length of 100" and distances of 2,000 and 5,000 light years.
  7. Corradi, R., Perinotto, M., Schwarz, H. and Claeskens, J. (1997). The chemical structure of bipolar planetary nebulae. I. IC 4406. Astronomy and Astrophysics, 322, pp.975-981. Online
  8. Sahai, R., Wootten, A., Schwarz, H. and Clegg, R. (1991). The bipolar planetary nebula IC 4406 - CO, optical and dust emission. Astronomy and Astrophysics, 251(2), pp.560-574. Online