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The first known globular cluster, now called M 22, was discovered in 1665 by Abraham Ihle, a German amateur astronomer. [4] [5] [6] The cluster Omega Centauri, easily visible in the southern sky with the naked eye, was known to ancient astronomers like Ptolemy as a star, but was reclassified as a nebula by Edmond Halley in 1677, [7] then finally as a globular cluster in the early 19th century ...
These are globular clusters within the halo of the Milky Way galaxy. The diameter is in minutes of arc as seen from Earth. For reference, the J2000 epoch celestial coordinates of the Galactic Center are right ascension 17h 45m 40.04s, declination −29° 00′ 28.1″. A high proportion of globular clusters are located in the Ophiuchus and ...
Horizontal branch. The horizontal branch (HB) is a stage of stellar evolution that immediately follows the red-giant branch in stars whose masses are similar to the Sun 's. Horizontal-branch stars are powered by helium fusion in the core (via the triple-alpha process) and by hydrogen fusion (via the CNO cycle) in a shell surrounding the core.
Other designations. NGC 7089 [8] See also: Globular cluster, List of globular clusters. Messier 2 or M2 (also designated NGC 7089) is a globular cluster in the constellation Aquarius, five degrees north of the star Beta Aquarii. It was discovered by Jean-Dominique Maraldi in 1746, and is one of the largest known globular clusters.
47 Tucanae is the second brightest globular cluster in the sky (after Omega Centauri), and is noted for having a small very bright and dense core. It is one of the most massive globular clusters in the Galaxy, containing millions of stars. The cluster appears roughly the size of the full moon in the sky under ideal conditions.
Estimated age. 13.5 ± 1.0 Gyr [7] Other designations. M80, NGC 6093, GCl 39 [8] See also: Globular cluster, List of globular clusters. Messier 80 (also known as M80 or NGC 6093) is a globular cluster in the constellation Scorpius. It was discovered by Charles Messier in 1781, being one of his first discoveries. [9]
Terzan 5. Terzan 5 is a heavily obscured globular cluster belonging to the bulge (the central star concentration) of the Milky Way galaxy. [3] It was one of six globulars discovered by French [7] astronomer Agop Terzan in 1968 [8] and was initially labeled Terzan 11. The cluster was cataloged by the Two-Micron Sky Survey as IRC–20385. [9]
Messier 3 is the prototype for the Oosterhoff type I cluster, which is considered "metal-rich". That is, for a globular cluster, Messier 3 has a relatively high abundance of heavier elements. [15] Arcturus and Cor Caroli can be used to help locate M3.