Galaxy in the constellation Cetus
NGC 157 is an intermediate spiral galaxy in the constellation of Cetus, positioned about 4° east of the star Iota Ceti. This galaxy can be viewed from suburban skies using a moderate-sized telescope. It was discovered on December 13, 1783 by William Herschel. The compiler of the New General Catalogue, John Louis Emil Dreyer noted that NGC 157 was "pretty bright, large, extended, between 2 considerably bright stars". It is a relatively isolated galaxy; the nearest other galaxy of comparable luminosity lies at a separation of .
The morphological classification of NGC 157 is SAB(rs)bc, indicating this is a weakly-barred spiral galaxy (SAB) with a transitional ring structure (rs) and moderate to loosely-wound arms (bc). The plane of the galaxy is inclined at an angle of 61.8° to the line of sight from the Earth. It has symmetric arms that become flocculent in the outer parts, breaking into multiple arms. The rotation curve for this galaxy undergoes a sharp decline, suggesting a low mass or a small dark matter halo. It is considered a quiescent galaxy, showing little star formation activity. However, there is a starburst region in the nucleus forming new stars at the rate of about one solar mass per year.
This galaxy has been host to two observed supernova events. The first, 2009em, was discovered 5 May 2009, about 34″ west and 10″ south of the galaxy core. It was determined to be a Type Ic supernova. On 5 May 2022, Type Ic supernova event SN 2022jli was observed in NGC 157, reaching a peak magnitude of 14.4.
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