Globular clusters are densely packed, spherical collections of hundreds of thousands or even millions of stars. They are among the oldest known objects in the Universe. The NASA/ESA Hubble Space Telescope has captured an amazing photo of one of these ancient objects — Messier 28.
This Hubble image shows the globular stellar cluster Messier 28. The image is a composite of separate exposures acquired by Hubble’s Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS). Seven filters were used to sample various wavelengths. The color results from assigning different hues to each monochromatic image associated with an individual filter. Image credit: NASA / ESA / Hubble / J.E. Grindlay et al.
Messier 28, also known as M28 and NGC 6626, is located 17,900 light-years away from Earth in the constellation Sagittarius.
This globular cluster was discovered by French astronomer Charles Messier on July 27, 1764, who catalogued it incorrectly, referring to it as a ‘[round] nebula containing no star.’
While today we know nebulae to be huge clouds of interstellar dust and gas, until the early 20th century a nebula represented any astronomical object that was not clearly localized and isolated. Any unidentified hazy light source could be called a nebula.
In fact, all 110 of the astronomical objects identified by Messier were combined under the title of the Catalogue of Nebulae and Star Clusters.
He classified many objects as diverse as star clusters and supernova remnants as nebulae. This includes Messier 28, which is actually a star cluster.
Whilst Messier 28 is easily recognizable as a globular cluster in this image, it is far less recognizable from Earth.
Even with binoculars it is only visible very faintly, as the distorting effects of the Earth’s atmosphere reduce this luminous ancient cluster to a barely visible smudge in the sky.
One would need larger telescopes to resolve single stars in Messier 28.
Fortunately, from space Hubble allows Messier 28 to be seen in all its beauty — far more than a faint, shapeless, nebulous cloud.
