NGC 457

Right Ascension	01 : 19.1 (h:m)
Declination	+58 : 20 (deg:m)
Distance	8.2 (kly)
Visual Brightness	6.4 (mag)
Apparent Dimension	13 (arc min)

Discovered by William Herschel in 1781.

Open Cluster NGC 457 was discovered by William Herschel on August 14, 1780, with his 6.2-inch reflector (7-ft. FL), as one of his early objects found before he started his systematical survey for nebulae and clusters. Just noticing but not cataloging the object, he found it again on October 18, 1787 with his 18.7-inch reflector of 20-ft FL, the standard instrument he used for the great survey, and cataloged it as H VII.42.

Modern parallax measurement has provided a value of about 8200 ly for this cluster's distance (between about 7400 and 9000 ly). Its age was estimated at about 21 million years. It was classified as of Shapley type "e" - an intermediately rich compact cluster, and as of Trumpler type "I,3,r" for detached and concentrated, a small reach of brightness, and rich (more than 100 member stars).

NGC 457 is one of the numerous open star clusters in the Milky Way in constellation Cassiopeia, and has been given a number of names by amateur and professional astronomers: The Dragonfly Cluster, the ET Cluster, the Owl Cluster, all for its appearance, and the Phi Cas Cluster for the brightest member star in its field, the yellow supergiant Phi Cassiopeiae; the membership probability of this bright star is often described as uncertain, but SIMBAD rates it as "100 %". The name "ET Cluster" was given because of its resemblance to the movie character "ET," when taking the bright stars Phi Cas (mag 5.0) and HR 7902 (mag 7.0) as its eyes.

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Wikipedia page for NGC 457

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Hartmut Frommert
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Last Modification: July 14, 2026