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Omega Centauri (NGC 5139) is the brightest and most spectacular globular cluster in the sky. Located in Centaurus and visible to the naked eye (mag. +3.7) it was believed by early astronomers to be star. In AD 140, Greek mathematician and astronomer Ptolemy included it in the "Almagest" his star catalogue. Using Ptolemy's data, Johann Bayer a German lawyer and uranographer (celestial cartographer) designated the "star" as Omega Centauri in his publication Uranometria (1603). It was Edmond Halley, in 1677, who first identified its non-stellar nature.
The cluster is best seen from southern locations during the months of March, April and May. From latitudes north of 42N it never rises above the horizon and can't be seen at all. It's listed as number 80 in the Caldwell catalogue.
The globular is positioned close to the middle of Centaurus. Located 5 degrees east of Omega is zeta Centauri (ζ Cen - mag. +2.6). About 15 degrees southeast of the globular are first magnitude stars Alpha and Beta Centauri and about the same distance on the southwestern side is the famous constellation of Crux, the Southern Cross.
NGC 869 and NGC 884 are two bright open clusters in the constellation of Perseus, that are separated by only half a degree of apparent sky. Together they are commonly known as the "Double Cluster" and form a famous showpiece object, that's easily visible to the naked eye and a wonderful sight in binoculars and telescopes. Both clusters have been known since antiquity and probably pre-historically. Greek astronomer Hipparchus first catalogued them around 130 B.C, with early celestial cartographers naming them as "h Persei" (NGC 869) and "χ Persei" (NGC 884).
The Double Cluster is located in the far northwestern part of Perseus, close to the border with Cassiopeia. With a declination of 57N, it's circumpolar from many northern locations and therefore never sets. To locate the object, draw an imaginary line from Mirfak (α Per - mag +1.8) in a northwesterly direction towards the centre of the "W" of Cassiopeia. The Double Cluster lies just over halfway along this line.
It's listed as number 14 in the Caldwell catalogue.
Finder Chart for NGC 869 and NGC 884 The Double Cluster - pdf format (credit:- freestarcharts)
NGC 2477 is a stunning open cluster located in the Milky Way rich constellation of Puppis. It's arguably the constellation's finest cluster, which also contains other superb examples such as M46, M47 and M93. At magnitude +5.8, NGC 2477 is faintly visible to the naked eye, but easily seen with binoculars and a fantastic telescope object especially in medium to large scopes. It's listed as number 71 in the Caldwell catalogue.
The cluster was discovered by French astronomer Nicolas Louis de Lacaille during his tour of South Africa in 1751-52. In total it contains about 300 stars packed into an area 27 arc minutes in diameter with the brightest member star shining at magnitude +9.8. The four-magnitude difference between the combined cluster magnitude and the brightest component is an indication of how rich the cluster is.
NGC 2477 is too far south to have been included in Charles Messier's catalogue, but if he had observed from a more southerly latitude than Paris he almost certainly would have noticed this striking object. Twentieth century America astronomer Robert Burnham described NGC 2477 as "probably the finest of the galactic clusters in Puppis".
The cluster is easily found 2 degrees northwest of zeta Pup (ζ Pup - mag. +2.2) and just northwest of magnitude +4.5 star, b Pup. Located 1.5 degrees west of NGC 2477, and in the same binocular field of view, lies large loose open cluster NGC 2451. Another binocular open cluster, NGC 2546, is positioned 4 degrees east of NGC 2477. They are best seen from southern latitudes during the months of December, January and February.
NGC 3626, mag. +10.9, is a spiral galaxy in Leo that was discovered by William Herschel on March 14, 1784. It's one of many galaxies in the constellation within the range of small scopes.
NGC 3626 is located 70 million light-years away. It covers 2.7 x 1.9 arc minutes of apparent sky, which corresponds to a spatial diameter of 55,000 light-years and is estimated to contain 40 billion stars.
Patrick Moore listed, NGC 3626, as number 40 in his Caldwell catalogue. It belongs to the NGC 3607 group of galaxies.
Finder Chart for NGC 3626 - pdf format (credit:- freestarcharts)
NGC 3626 is positioned 2.5 degrees southeast of Zosma (δ Leo - mag. +2.6). A trio of elliptical galaxies, consisting of NGC 3607, NGC 3608 and NGC 3605, are located 50 arc seconds west-southwest of NGC 3626. Of these, NGC 3607 is the brightest at magnitude +9.9. NGC 3608 is similar in brightness to NGC 3626. At 12th magnitude the third member, NGC 3605, is by far the faintest.
47 Tucanae or 47 Tuc is a spectacular globular cluster located in the southern constellation of Tucana. At magnitude +4.5, it appears to the naked eye as a slightly fuzzy star similar to the head of a tail-less comet. Always hidden from view for European and North American observers, 47 Tuc was discovered by French astronomer Nicolas Louis de Lacaille on September 14, 1751. Initially Lacaille though he had found a comet until further inspection revealed its true nature.
47 Tuc is the second brightest globular in the sky, only Omega Centauri is more brilliant. It has an extremely dense core and is one of the most massive globular clusters surrounding the Milky Way. The cluster is located 2.5 degrees west of the Small Magellanic Cloud (SMC) and from most of the Southern Hemisphere it's circumpolar and never sets. In contrast from latitudes of 18N or greater, the globular can never be seen as it fails to rise above the horizon.
Through 7x50 or 10x50 binoculars, 47 Tuc appears as a bright starlight nucleus surrounding by a halo of soft pearly light. It's clearly non-stellar in nature. Telescopically the cluster is stunning and a showpiece object of the night sky. It total it spans 31 arc minutes of apparent sky, almost exactly the same diameter as the full Moon. For comparison, 47 Tuc is 50% larger and 3x brighter than M13 "the Great Hercules Globular Cluster" widely regarded as the finest globular in the northern section of the sky.
A small 100mm (4-inch) scope reveals a bright compact core surrounded by a large 15 arc minute sphere with the brightest members resolvable. Even through small telescopes it's a superb sight. A 200mm (8-inch) instrument shows a swarm of stars in a glittering 3D view. The dense centre remains unresolvable in stark contrast to the less dense outer regions. Overall it's a breathtaking object for all sizes and types of telescopes.
NGC 457 is the brightest open cluster in Cassiopeia and one of the finest objects of its type in the northern sky. At magnitude +6.4, it's just beyond naked-eye visibility but easily seen with binoculars and a beautiful sight through telescopes. The brightest cluster stars are arranged in prominent lines and curves that resemble an Owl shape, hence the popular name "The Owl Cluster".
NGC 457 was discovered by William Herschel in 1787. Finding the Owl Cluster is easy as it's located two degrees south-southeast of eclipsing binary star system Ruchbah (δ Cas - mag. +2.7). This star is one component of the characteristic "W" asterism of Cassiopeia. The brightest star inside NGC 457 is Phi Cassiopeiae (φ Cas - mag. +5.0). Despite not being a member of the cluster, this foreground star is visible to the naked eye. Together with another non-cluster star, seventh magnitude HD 7902 (HIP 6229), they form the bright eyes of the Owl.
NGC 457 is best seen from Northern Hemisphere latitudes during August, September and October. It appears high in the sky and even overhead from many locations. From latitudes greater than 32N, the Owl is circumpolar and therefore never sets.
Finder Chart for NGC 457 - pdf format (credit:- freestarcharts)
NGC 2261 is a curious reflection nebula in Monoceros that's known as Hubble's Variable Nebula. It was discovered by William Herschel in 1783 and is illuminated by variable star R Monocerotis (R Mon). The nebula is unusual in that it changes shape over a period of just days and can vary by up to 2 magnitudes in brightness. The variations are believed to be due to periodic changes in the amount of dust surrounding R Mon, thus affecting the amount of light that reaches us. With an apparent magnitude of +9.0, it can be spotted with binoculars under dark skies.
The variability of R Mon (between magnitudes +10 and +12) was discovered at the Athens Observatory in 1861, but it wasn't until 1916 when Edwin Hubble realised that the nebula also changes in brightness. The variations are such that even on images taken only days apart, structural changes can be seen.
NGC 2261 was chosen as the "first light" photograph on January 26, 1949 for the 200-inch (5.1 m) Hale reflecting telescope under the direction of American astronomer Edwin Powell Hubble. At the time, the newly constructed Hale telescope was the largest telescope in the world and remained so until 1976. NGC 2261 is number 46 in the Caldwell catalogue.
NGC 4755, also known as the Jewel Box or Kappa Crucis Cluster, is one of the finest open clusters in the sky. It's located in the small southern constellation of Crux and at magnitude +4.2 is bright enough to be seen with the naked eye. It contains over 100 stars, mostly blue or red, spread over 10 arc minutes of apparent sky. This cluster is one of a handful of night time objects that offers something for all observers of all telescope sizes.
NGC 4755 is located 6,440 light-years distant and is best seen from southern latitudes during the months of March, April and May. It's circumpolar from locations south of 30S and can also be seen from the tropics, although for many Northern Hemisphere observers it never rises above the southern horizon.
NGC 891 is a tenth magnitude unbarred spiral galaxy located in Andromeda. Also known as the Silver Sliver, it's one of the best examples of an edge-on galaxy in the sky although a challenging object for small scopes. Due to its attractiveness and scientific appeal, NGC 891 was selected on October 12, 2005 to be the first light image of the Large Binocular Telescope at Mount Graham International Observatory in Arizona. In 2012, it was again selected as first light image, this time for the Discovery Channel Telescope (DCT) Large Monolithic Imager at the Lowell Observatory in Happy Jack, Arizona.
The Silver Sliver was discovered by William Herschel on October 6, 1784 and is best seen from the Northern Hemisphere during October, November and December. Astronomers think our Milky Way galaxy would look remarkably similar, if viewed edge-on.
Finder Chart for NGC 891 - pdf format (credit:- freestarcharts)
The Silver Sliver is located in eastern Andromeda close to the Perseus border. It's positioned 3.5 degrees east of beautiful double star Almach (γ And - mag. +2.1) with naked-eye open cluster M34 (mag. +5.5) a further 3.5 degrees to the east.