Globulars

Glob1	Globular cluster M13 is the brightest globular cluster visible from northern temperate latitudes. In very dark moonless skies it can be seen as a fuzzy patch with the naked eye. It is easily visible in binoculars. M13 is about 21,000 light years away in the constellation Hercules. The cluster has a diameter of about 160 light years, and contains a million stars! Here is an interesting discussion of M13 from Burnham's Celestial Handbook: "In the actual center of the cluster the star density may be (great), but in no case would it approach actual crowding. This fact is better understood by constructing an imaginary scale model of the cluster. On such a model the stars would be represented by a million grains of sand, distributed throughout a spherical volume ... some 300 miles in diameter. Each grain would be .03 inches in diameter, and separated from the next nearest grain by 3 miles! Even in the most closely packed central mass, the grains would still be separated ... by the greater part of a mile. Thus, even the globular cluster, which appears to us the most densely packed mass of stars to be found anywhere in the Universe, is shown to be by earthly standards almost empty space." "The appearance of the heavens from a point within the Hercules cluster would be a spectacle of incomparable splendor; the heavens would be filled with uncountable numbers of blazing stars which would dwarf our own Sirius and Canopus to insignificance. Many thousands of stars ranging in brilliance between Venus and the full moon would be continually visible, so there would be no real night at all on a planet in a globular cluster."
Glob2	The globular cluster Messier 15 is shown in this color image obtained with the NASA Hubble Space Telescope's Wide Field Planetary Camera 2 (WFPC2). Lying some 40,000 light-years from Earth in the direction of the constellation Pegasus, M15 is one of nearly 150 known globular clusters that form a vast halo surrounding our Milky Way galaxy. Each of these clusters is a spherical association of hundreds of thousands of ancient stars. The image, prepared by the Hubble Heritage team, attempts to show the stars in M15 in their true colors. The brightest cluster stars are red giants, with an orange color due to surface temperatures lower than our Sun's. Most of the fainter stars are hotter, giving them a bluish-white color. Nestled among the myriads of stars visible in the Hubble image is an astronomical oddity. The pinkish object to the upper left of the cluster's core is a gas cloud surrounding a dying star. Known as Kuestner 648, this was the first planetary nebula to be identified in a globular cluster. In 1928, F. G. Pease, working at the 100-inch telescope of California's Mount Wilson Observatory, photographed the spectrum of K 648 and discovered the telltale bright emission of a nebular gas cloud rather than a normal star. In the ensuing 70 years, only three more planetary nebulae have been discovered in globular clusters. The stars in M15 and other globular clusters are estimated to be about 12 billion years old. They were among the first generations of stars to form in the Milky Way. Our Sun, by comparison, is a youthful 4.6 billion years old. As a star like the Sun ages, it exhausts the hydrogen that fuels its nuclear fusion, and increases in size to become a red giant. Then it ejects its outer layers into space, producing a planetary nebula. The remnant star at the center of the nebula gradually dies away as a white dwarf. Planetary nebulae are so named because their shapes reminded 18th-century astronomers with small telescopes of the round disks of planets. They are actually huge clouds of gas, glowing because of ultraviolet light emitted by the stars in their centers. The surface temperature of the central star of K 648 is about 70,000 degrees Fahrenheit (40,000 degrees Celsius), and analysis of the Hubble data indicates that the star's remaining mass is only 60 percent that of our Sun. The star's outer layers were ejected some 4,000 years ago.
Glob3	The globular cluster M19.
Glob4	The globular cluster 47 Tucanae.
Glob5	Located some 17,000 light-years from Earth, Omega Centauri is a massive globular star cluster, containing several million stars swirling in locked orbits around a common center of gravity. The stars are packed so densely in the cluster's core that it is difficult for ground-based telescopes to make out individual stars. Hubble's high resolution is able to pick up where ground-based telescopes leave off, capturing distinct points of light from stars at the very center of the cluster. Omega Centauri is the most luminous and massive globular star cluster in the Milky Way. It is one of the few globular clusters that can be seen with the unaided eye. Named by Johann Bayer in 1603 as the 24th brightest object in the constellation Centaurus, it resembles a small cloud in the southern sky and might easily be mistaken for a comet. Omega Centauri is so large in our sky that only a small part of it fits within the field of view of the Wide Field and Planetary Camera 2 (WFPC2) on the Hubble Space Telescope. Yet even this tiny patch contains some 50,000 stars, all packed into a region only about 13 light-years wide. For comparison, a similarly sized region centered on the Sun would contain about a half dozen stars. The vast majority of stars in this Hubble image are faint, yellow-white dwarf stars similar to our Sun. The handful of bright yellow-orange stars are red giants that have begun to exhaust their nuclear fuel and have expanded to diameters about a hundred times that of the Sun. A number of faint blue stars are also visible in the image. These are in a brief phase of evolution between the dwarf stage and the red-giant stage, during which the surface temperature is high. The stars in Omega Centauri are all very old, about 12 billion years. Stars with a mass as high as that of our Sun have already completed their evolution and have faded away as white dwarfs, too faint to be seen even in the Hubble image.
Glob6	NGC 1818 is a young globular cluster in the Large Magellanic Cloud
Glob7	The globular cluster M10 contains many red giant stars. This means it has been around long enough for many stars to evolve into the red giant stage.
Glob8	A simulation of 100 stars interacting gravitationally similar to the stars in a globular cluster. Hundreds of years pass during one second in this movie.
Glob9	Globular Cluster M3 is about 100,000 light years away in the constellation Canes Venatici. It is about 150 light years in diameter.