We must see 101 cosmic objects: M55

M55 is one of the most beautiful clusters of globular stars in the night sky. It is also one of the most southerly globes in Charles Messier’s catalog. It was discovered by Abbe Nicolas Louis de Lacaille in 1751 while surveying the southern stars from the Cape of Good Hope. Through his small telescope (lower than today’s telescope) he recorded it as resembling the “faint nucleus of a large comet”. Messier’s report wasn’t much different: “a white patch 6 inches wide.”

Today we know this close (about 17,600 light-years) and ancient remnant filaments (about 12.5 billion years old) with as many as 100,000 suns scattered loosely across 100 light-years of space. This large swarm of gravitationally bound starlight is approaching us at more than 100 miles per second (62 kilometers per second) in an elliptical orbit curving through our galaxy’s distant corona.

While all globular clusters are richly populated with old, metal-poor stars, M55 is exceptional in this respect: On average, its stars contain only about 1 percent of the portion of heavy metals found in our sun, making M55 one of the most metal-rich groups. Poor spherical stars are well known. It also has a potential tidal extension – not visible to amateur equipment – which could be caused by tidal shocks that strike the cluster as it takes its orbit to flip through the Milky Way’s disk.

Under a dark sky (which is required to see this group well), keen-eyed observers spied the glow of his sixth force without visual aid about 8° east to the southeast of Zeta (ζ) arc. Binoculars will display the mass well, as a homogeneous glistening star. The telescopic view becomes even more impressive with the addition of power. At low energy, uniform fragments of the cluster glow in whispers from the hull. The cluster begins to open 70-fold when some of its brightest organs (Fate 11) pulse in and out of view across the 20-foot-wide spherical face. Higher magnifications highlight more stars. Those in M55 shine on the horizontal branch – the stage of stellar life in which red giants evolve – with an average magnitude of 14.4, meaning medium-sized telescopes can reasonably resolve the mass.


Make sure to explore astronomy The complete list of 101 cosmic objects you must see. New entries will be added every week throughout 2022.

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