M19 is a globular cluster in the constellation of Ophiuchus, located about nine degrees above (north) of the galactic plane and slightly west of the line of sight from Earth to the galactic center. It's actually on the opposite side of the galactic center from Earth, so despite being over 28000 light-years from Earth, M19 is one of the Messier globulars closest to the center of the Milky Way, at a little more than 5000 light-years. M19 is moving away from us at a rate of 146 kilometers per second. M19 is a rich, fairly dense globular cluster, and one of the most elongated. The distance along its major axis is around 65 light-years. The brightest stars have an average magnitude of 14.8, and although its total absolute magnitude is -9, the apparent magnitude to us is 6.8. This is bright enough for easy viewing through binoculars and small telescopes. Because of its location near the plane and central region of the Milky Way, it has a background of faint dust and appears embedded in a rich field of stars. As with other globular clusters, which are the oldest, densest, and most populous star clusters in the Milky Way, M19 is made up of stars that are all the same age. These are amongst the oldest stars in our Galaxy, at an age of about 13 billion years. Because the stars in a globular cluster are all the same age and all at the same distance from Earth, they provide an excellent laboratory in which astronomers can study stellar evolution. The stars of a globular cluster can also be used to understand "standard candles", which is to say, types of stars that all have the same intrinsic brightness, and can therefore be used to measure distances. One such type is RR-Lyrae variables, only four of which are observed in M19. This picture was created from six images taken in July 1997 at the KPNO 0.9-meter telescope during the summer Research Experiences for Undergraduates (REU) program operated at the Kitt Peak National Observatory and supported by the National Science Foundation. Image size 15.9x15.5 arc minutes.
