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NGC 457
NGC 457
	Open cluster NGC 457 in Cassiopeia
Observation data (J2000.0 epoch)
Right ascension	01h 19m 32.6s
Declination	+58° 17′ 27″
Distance	7.922 kly (2.429 kpc)
Apparent magnitude (V)	6.4
Apparent dimensions (V)	13.0′
Physical characteristics
Other designations	Owl Cluster, E.T. Cluster, Caldwell 13, Cr 12, Mel 7, OCL 321, Lund 43, H VII-42, h 97, GC 256,
Associations
Constellation	Cassiopeia
	See also: Open cluster, List of open clusters

NGC 457 (also designated Caldwell 13, and known as the Dragonfly Cluster, E.T. Cluster, Owl Cluster, Kachina Doll Cluster or Phi Cassiopeiae Cluster)^[2] is an open star cluster in the constellation Cassiopeia.

Discovery

It was discovered by William Herschel on August 18, 1780, with a 6.2 inch reflector telescope, and catalogued as VII 42.^[3]

Visibility

It is an easy target for amateur astronomers, and can be seen even with small telescopes in light-polluted skies.

Characteristics

It lies over 7,900 light years away from the Sun. It has an estimated age of 21 million years.^[1] The cluster is sometimes referred by amateur astronomers as the Owl Cluster^[4] or the E.T. Cluster (due to its resemblance to the movie character). Two bright stars Phi Cassiopeiae (magnitude 5 and spectral type F0) and HD 7902 (magnitude 7) can be imagined as eyes. It is not yet clear if Phi Cassiopeiae is a member of the cluster, and if it is, then it would be one of the brightest stars known, surpassing Rigel in luminosity. For comparison, the Sun at the same distance as Phi Cassiopeiae would shine at just 17.3 magnitude. The next brightest star is the red supergiant variable star V466 Cassiopeiae. The cluster features a rich field of about 150 stars of magnitude 9-13. About 60 stars have been identified as true members of the cluster.

Gallery

NGC 457 and NGC 436 — NGC 457 (center) pictured alongside open cluster NGC 436 (bottom right).

References

^ ^a ^b Frinchaboy, Peter M.; et al. (2008). "Open Clusters as Galactic Disk Tracers. I. Project Motivation, Cluster Membership, and Bulk Three-Dimensional Kinematics". The Astronomical Journal. 136 (1): 118–145. arXiv:0804.4630. Bibcode:2008AJ....136..118F. doi:10.1088/0004-6256/136/1/118. S2CID 16641439. See table I, p. 12.
^ "The Dragonfly Cluster (Open Cluster)". Retrieved 2020-10-28.
^ "NGC 457, Owl Cluster, E.T. | Deep⋆Sky Corner". www.deepskycorner.ch. Retrieved 2022-05-28.
^ "NGC 457". Astronomy Magazine. Retrieved 2020-10-13.