Type: Open Cluster, Trumpler Class I2r
Distance: 11.000 ly
Size: 12’
Mag: 7.6V
Brightest Star: 11.0V
Till the beginning of the 20’th century the real nature of all “nebula objects” was not exactly known. Herschel already suspected that all nebula's exist of stars which can not be resolved at all objects.
The situation improves with the large “Leviathan” – the 72-inch telescope of Lord Rosse. He first saw spiral structure in some objects and named them in a new classification. His idea was to resolve as many “nebula's”, also “Spirals”, as the telescope could show. And he seems to win the fight with some objects – one of it our OOTW NGC 2506.
In his second paper 1861 he described the cluster as: “frequently observed, several observers have fancied that the stars exhibit some approach to a spiral arrangement, with cellular center, not unresolved neby”. His son Lawrence wrote for example: “more approach towards spiral appearance than I have seen in other cluster…the spiral appearance is confined to the brightest stars…”
Today we knew that NGC 2506 is a normal, old, metal poor cluster in a average distance.
Sadly the cluster can not be resolved in telescopes of the 4-inch class. With aperture of 8/10-inch+ the spiral structure can be detected. Even in big telescopes the clusters remains interesting because of its star rich appearance. What can you see? And still remember Lord Rosse between his walls and in front of his large telescope.
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