Messier 28

Template:Short description {{#invoke:other uses|otheruses}} Template:Infobox globular cluster

Messier 28 or M28, also known as NGC 6626, is a globular cluster of stars in the center-west of Sagittarius. It was discovered by French astronomer Charles Messier in 1764.<ref name=thompson2007/>Template:Efn He briefly described it as a "nebula containing no star... round, seen with difficulty in 3Template:Frac-foot telescope; Diam 2′."<ref name=burnham1979/>

In the sky it is less than a degree to the northwest of the 3rd magnitude star Kaus Borealis (Lambda Template:Abbreviation). This cluster is faintly visible as a hazy patch with a pair of binoculars<ref name=thompson2007/> and can be readily found in a small telescope with an Template:Convert aperture, showing as a nebulous feature spanning 11.2 arcminutes. Using an aperture of Template:Convert, the core becomes visible and a few distinct stars can be resolved, along the periphery. Larger telescopes will provide greater resolution,<ref name=inglis2004/> one of Template:Convert revealing a dense 2′ core, with more density within.<ref name=thompson2007/>

It is about 18,300 light-years away from Earth.<ref name=Oliveira/> It is about Template:Val<ref name=apj742_1_51/> and its metallicity (averaging −1.32 which means more than 10 times less than our own star), coherency and preponderence of older stellar evolution objects, support its dating to very roughly 12 billion years old.<ref name=mnras385_4_1998/> 18 RR Lyrae type variable stars have been found within.

It bore the first discovery of a millisecond pulsar in a globular cluster – PSR B1821–24. This was using the Lovell Telescope at Jodrell Bank Observatory, England.<ref name="jbo_stars">Template:Cite web</ref> A total of 11 further of these have since been detected in it with the telescope at Green Bank Observatory, West Virginia. As of 2011, these number the third-most in a cluster tied to the Milky Way, following Terzan 5 and 47 Tucanae.<ref name=apj730_2_81/>

Gallery

• Messier 28 taken by Hubble.<ref>Template:Cite web</ref>
  Messier 28 taken by Hubble.<ref>Template:Cite web</ref>
• 2.5' view of M28 taken by Hubble Space Telescope.
  2.5' view of M28 taken by Hubble Space Telescope.
• Messier 28 on 2MASS; wide angle
  Messier 28 on 2MASS; wide angle
• Map showing location of M28
  Map showing location of M28

See also

• List of Messier objects

External links

• Globular Cluster M28 @ SEDS Messier pages
• Messier 28, Galactic Globular Clusters Database page
• Template:WikiSky