M55 is among the most unsung but stunning globular star clusters within the night time sky. It’s additionally one of the crucial southerly globulars in Charles Messier’s catalog. Abbe Nicolas Louis de Lacaille found it in 1751 whereas surveying the southern stars from the Cape of Good Hope. By way of his small telescope (inferior to as we speak’s binoculars) he recorded it as wanting just like the “faint nucleus of a giant comet.” Messier’s report of it was not a lot totally different: “a whitish patch about 6′ throughout.”
At this time we all know this shut (about 17,600 light-years distant) and historic (roughly 12.5 billion years outdated) relic bristles with as much as maybe 100,000 suns unfold loosely throughout 100 light-years of space. This senior swarm of gravitationally certain starlight is approaching us at greater than 100 miles per second (62 kilometers per second) on an elliptical orbit that arcs by means of the distant halo of our galaxy.
Whereas all globular clusters are richly populated with metal-poor aged stars, M55 is phenomenal on this regard: On common, its stars have solely about 1 p.c of the fraction of heavy metals present in our Solar, making M55 one of the crucial metal-poor globular star clusters identified. It additionally has a doable tidal extension — not seen to novice tools — which might be brought on by the tidal shocks that buffet the cluster when its orbit takes it swooping by means of the disk of the Milky Way.
Underneath darkish skies (that are required to see this cluster effectively), keen-eyed observers have spied its Sixth-magnitude glow with out optical help about 8° east-southeast of Zeta (ζ) Sagittarii. Binoculars will current the cluster effectively, as a uniformly furry star. The telescopic view turns into more and more extra magnificent as energy is added. At low energy, the cluster’s uniform glow splinters into teasing whispers of construction. The cluster begins to blossom at 70x when a few of its brighter members (eleventh magnitude) pulse out and in of view throughout the globular’s 20′-wide face. Larger magnifications convey out extra stars. These in M55 on the horizontal department — the stage of stellar life that pink giants evolve into — shine at a mean magnitude of 14.4, which means that moderate-sized telescopes can resolve the cluster moderately effectively.
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