Hubble sequence

The Hubble sequence is a morphological classification scheme for galaxies published by Edwin Hubble in 1926.^[1]^[2]^[3]^[4] It is often colloquially known as the Hubble tuning-fork diagram because the shape in which it is traditionally represented resembles a tuning fork. It was invented by John Henry Reynolds and Sir James Jeans.^[5]

The tuning fork scheme divided regular galaxies into three broad classes – ellipticals, lenticulars and spirals – based on their visual appearance (originally on photographic plates). A fourth class contains galaxies with an irregular appearance. The Hubble sequence is the most commonly used system for classifying galaxies, both in professional astronomical research and in amateur astronomy.

^ Hubble, E.P. (1926). "Extra-galactic nebulae". Contributions from the Mount Wilson Observatory / Carnegie Institution of Washington. 324: 1–49. Bibcode:1926CMWCI.324....1H.
^ Hubble, E.P. (1926). "Extra-galactic nebulae". Astrophysical Journal. 64: 321–369. Bibcode:1926ApJ....64..321H. doi:10.1086/143018.
^ Cite error: The named reference hubble27 was invoked but never defined (see the help page).
^ Hubble, E.P. (1936). The realm of the nebulae. Mrs. Hepsa Ely Silliman memorial lectures. Vol. 25. New Haven: Yale University Press. ISBN 9780300025002. LCCN 36018182. OCLC 611263346 – via Internet Archive (archive.org). Hubble, Edwin Powell (January 1982). Alt source. Yale University Press. ISBN 0300025009 – via Google Books.
^ Block, David L.; Freeman, Ken C. (2015) [14 November 2014]. Freeman, Kenneth; Elmegreen, Bruce; Block, David; Woolway, Matthew (eds.). Lessons from the Local Group. 2014 International conference honoring David Block and Bruce Elmegreen, focusing on the Local Group as an example of galactic-scale processes (softcover ed.). Switzerland: Springer Cham / Springer International Publishing (published 10 September 2016). pp. 1–20. Bibcode:2015llg..book....1B. doi:10.1007/978-3-319-10614-4_1. ISBN 978-3-319-37812-1; (hardcover ed.) ISBN 978-3-319-10613-7 (published 3 December 2014);
"ADS abstract". NASA / Astrophysics Data System. Harvard University. 2015. Bibcode:2015llg..book....1B.

[hubble26a-1] Hubble, E.P. (1926). "Extra-galactic nebulae". Contributions from the Mount Wilson Observatory / Carnegie Institution of Washington. 324: 1–49. Bibcode:1926CMWCI.324....1H.

[hubble26-2] Hubble, E.P. (1926). "Extra-galactic nebulae". Astrophysical Journal. 64: 321–369. Bibcode:1926ApJ....64..321H. doi:10.1086/143018.

[hubble27-3] Cite error: The named reference hubble27 was invoked but never defined (see the help page).

[Hubble-1936-4] Hubble, E.P. (1936). The realm of the nebulae. Mrs. Hepsa Ely Silliman memorial lectures. Vol. 25. New Haven: Yale University Press. ISBN 9780300025002. LCCN 36018182. OCLC 611263346 – via Internet Archive (archive.org). Hubble, Edwin Powell (January 1982). Alt source. Yale University Press. ISBN 0300025009 – via Google Books.

[5] Block, David L.; Freeman, Ken C. (2015) [14 November 2014]. Freeman, Kenneth; Elmegreen, Bruce; Block, David; Woolway, Matthew (eds.). Lessons from the Local Group. 2014 International conference honoring David Block and Bruce Elmegreen, focusing on the Local Group as an example of galactic-scale processes (softcover ed.). Switzerland: Springer Cham / Springer International Publishing (published 10 September 2016). pp. 1–20. Bibcode:2015llg..book....1B. doi:10.1007/978-3-319-10614-4_1. ISBN 978-3-319-37812-1; (hardcover ed.) ISBN 978-3-319-10613-7 (published 3 December 2014);
"ADS abstract". NASA / Astrophysics Data System. Harvard University. 2015. Bibcode:2015llg..book....1B.

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