Collinder 160

Collinder 160 is a young, fairly compact open star cluster in the constellation Puppis, also known as Cr 160, NGC 2447 and Messier 93 (M93). It is about 3,400 to 3,600 light-years away and spans about 22 arcminutes, roughly 20 to 25 light-years, with a much smaller bright core. Sources give “about 100” members, but I did not find a Gaia membership count to verify this. It stands out for its wedge or starfish shape, which some observers also describe as a butterfly or arrowhead. It contains several red giants (between three and eight, depending on the source) and, according to a 2018 study, four spectroscopic binaries, one of which features a “yellow straggler” star. Its age is uncertain: about 100 million years from its brightest main-sequence stars, but 387 to 400 million years from fits to the red giants. Charles Messier discovered it on 20 March 1781, his last original discovery, and Caroline Herschel independently found it in 1783.