Planetary Nebula Minkowski 2-51 + Cluster NGC 7235
The planetary nebula Minkowski 2-51 (PK 103+0.1) was discovered in 1947 by the German-American astronomer Rudolph Minkowski on photo plates in the Newton focus of the 60 inch or 100 inch telescope on Mount Wilson. Minkowski also contributed to the creation of the National Geographic Society - Palomar Observatory Sky Survey (POSS). 
|Designations||PN G103.2+00.6: M 2-51, PK 103+00.1, ARO 369, VV 272, VV' 559|
|Right Ascension (J2000.0)||22h 16m 04s|
|Declination (J2000.0)||57° 28' 42"|
|Radial Velocity||-11.0 km/s ± 25.0 km/s|
|Expansion Velocity||10.5 km/s (O-III)|
|C-Star Designations||AG82 437bis|
|C-Star Magnitude||19.2 mag (B filter), 20.4 mag (V filter)|
Open Cluster NGC 7234 = NGC 7235
On October 16, 1787, the German-British astronomer William Herschel discovered a star cluster with his self-made 18.7 inch reflecting telescope in Bath, England, which was noted with the designation (WH) VIII 63 and the description «Star clusters, small, poor, little crowded».  Unfortunately, Herschel made a mistake when determining his position, because there was nothing at the position given. On September 24, 1829, his son John scoured the same area with his 18.3 inch reflector telescope and recorded a star cluster as h 2154, which he described as «star cluster, pretty much crowded with ruby red star 10th magnitude». 
The error in Wilhelm Herschel's position specification was discovered in 1862 by the German astronomer Arthur von Auwers. He recognized that the star clusters WH VIII 63 (GC 4771) and h 2154 (GC 4772) had to be one and the same object and published his findings. But that must have escaped John Herschel when he published his «General Catalogue of Nebulae and Clusters of Stars» in 1864. There the supposedly two star clusters were listed as GC 4771 and GC 4772. Thus, John L. E. Dreyer also adopted this mistake when he published the «New General Catalog of Nebulae and Clusters of Stars»  in 1888. There WH VIII 63 was listed as NGC 7234 and JH 2154 as NGC 7235. [196, 277] The error persists to this day. In the SIMBAD Astronomical Database  and in the NASA / IPAC Extragalactic Database (NED)  only NGC 7235 are listed.
The Swedish astronomer Per Collinder lists the star cluster under the number 477 in his “Catalog of Open Galactic Clusters” published in 1931. He gives an angular size of 5 x 2.5 arc minutes and a number of 12 stars.  According to WEBDA , the star cluster is 2823 pc away and its age is estimated to be around 12 million years.
|NGC 7234||22 12 24.0||+57 16 24||OCL (II3m)||8.6||7.7||6.00||Cl, S, P, lC||NGC 7235, OCL 229|
|NGC 7235||22 12 24.0||+57 16 24||II3m||8.6||7.7||6.00||Cl, pC, has a ruby * 10||NGC 7234, OCL 229|
The planetary nebula Minkowski 2-51 is located in the constellation Cepheus. The open star cluster NGC 7235 and the two stars ε Cephei (4.1 mag) and HR 8506 (5.8 mag) help with the search. The best time to observe is May to December, when it is highest at night.