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Targets for Small to medium Telescopes IISAC October, 2009 Prepared by: John Bambury NGC 6752 (The Starfish or Pavo Globular) Image Credit: Anglo-Australian Observatory/David Malin Constellation: RA: Dec: TYPE: Visual Magnitude Size: Distance: Pavo 19h 10’ 51.8” -59 58 55” Globular Cluster 5.3 29’ ~13,000 ly General Object Information NGC 6752 is known as “The Starfish” or the “Pavo Glob” . It is also catalogued as Caldwell 93. The globular was discovered in 1827 by James Dunlop. The apparent size of this globular is somewhat open to discussion, O’Meara lists it as 29’ but some other reputable sources, including Hartung and Burnham, list it as 15’. The Central Core of NGC 6752 is very small and compressed and covers an apparent diameter of 2.5’. The stars external to the core extend outwards in looped arms and resemble a Starfish. Some see it as resembling a butterfly, which in my opinion it does somewhat more so than M6, the Open Cluster so named. NGC 6752 is one of over 20 Milky Way Globular Clusters which have undergone a “core collapse”. NGC 6752 is one of the closest and brightest globulars to us and is one of the easiest to resolve in small telescopes. An attractive double star h 5085 is also included within the outliers. This was one of Hartung’s favourite targets and without doubt makes the top 10 globulars list. It is a wonderful target in any instrument over about 4” aperture. It is visible naked eye under excellent sky conditions. NGC 2070 (The Tarantula Nebula) Image Credit: R Jay GaBany. Constellation: RA: Dec: TYPE: Visual Magnitude Size: Distance: Dorado 5h 38.6m -6905 Emission Neb + Cluster ~4.0-5.3 30’x20’ ~170,000 ly General Object Information NGC 2070 is known as the Tarantula Nebula. It is also catalogued as Caldwell 103. Also sometimes known as 30 Doradus. It was discovered in ~1751 by Lacaille. It is a massive and luminous HII region, located within the Large Magellanic Cloud. It is the largest known HII region within the local group of Galaxies. The entire nebula spans 3,000 ly, which compares to the Orion Nebula spanning 40 ly. The Star Cluster at the Centre of the Nebula (also NGC 2070), spans 250 light years. If the nebula were contained within our own Galaxy it would fill the entire constellation of Orion (30 degrees of sky) and darkness as we know it, would not exist.. The cluster contains a very large number of type O3 blue supergiants. These are generally smaller than their red counterparts, but are amongst the hottest and most luminous stars known. The Clusters’ mass is over 200,000 suns, with the stars gravitationally bound. It is believed with this much mass NGC 2070 could harbour a globular cluster in the making. Telescopically the Tarantula Nebula is one of the night Sky’s stunning targets. Any telescope over 3” aperture will reveal its swarms of knots and loops together with the central star cluster. The telescopic view of the nebulosity itself is enhanced with a UHC or OIII filter, but these filters dampen the starlight from the central cluster. This is an easy naked eye target under dark skies. NGC 104 (47 Tucanae) Image Credit: Emmanuel BEAUDOIN Const: Type: Visual Mag: RA: DEC: Diameter: Distance: Tucana Globular Cluster 3.9 0h 24’ 5.2” -72° 4’ 51” 50’ ~14,700 ly General Object Information NGC 104 is known as 47 Tucanae. It is also catalogued as Caldwell 106. It was discovered in 1751 by Lacaille. It is located 2.5° off the Western edge of the Small Magellanic Cloud. It is the second brightest globular in the sky (.2 mag behind Omega Centauri) and 3 times brighter (1.25 mags) than the brightest Messier Globular (M22). The Cluster spans 214 light years. 47 Tuc contains a large number of blue stragglers. One of these, BSS-19, is the first blue straggler whose mass has been recorded. Recent data from the Hubble Faint Object Spectrograph in respect of BSS-19 indicates a slow merger of a binary pair has occurred, as opposed to a collision resulting from a core collapse. 47 Tuc is one of the night Sky’s stunning targets. In my opinion it is the finest globular cluster in the entire sky. Any telescope over 4” aperture will resolve it to the core. It contains a very bright blazing condensed core, with a soft radiating glow as you move away from the core. Many people see colour in 47 Tuc. Some see it having a soft yellow appearance. Others see it with a pinkish hue. I have seen both in varying apertures. An interesting additional target for larger scopes is NGC 121. This is an 11.2 magnitude globular cluster located 30’ north northeast of the central core. It is small at 1.5’ x 1.5’ but should be visible in medium apertures under good skies. This is an easy naked eye target under regional skies. M11 (Wild Duck Cluster) Image Credit: NASA Const: Type: Visual Mag: RA: DEC: Diameter: Distance: Scutum Open Cluster 5.8 18h 51’ 6” 6° 16’ 12” 13’ ~5,460 ly General Object Information M11 is known as The Wild Duck Cluster. It is also catalogued as NGC 6705. It was discovered in 1681by Gottfried Kirsch. It is located 2° southeast of Beta Scuti. It sits in a notch in the north edge of the Scutum star cloud. The cluster contains about 680 stars, 400 of which shine at brighter than 14th magnitude. The cluster spans 20 light years. This is a very compressed open cluster and the nucleus reminds me of a globular cluster falling apart. Unlike the summer, autumn and winter skies, the spring sky is a little light on for bright open clusters. This is one of the better ones. It is an easy naked eye target under dark skies. NGC 7293 (The Helix Nebula) Image Credit: NASA, WIYN, NOAO, ESA, Hubble Helix Nebula Team, M. Meixner (STScI), & T. A. Rector (NRAO) Const: Type: Visual Mag: RA: DEC: Diameter: Distance: Aquarius Planetary Nebula 6.0~7.3 22h 29’ 38.4” -20° 50’ 13” 12’ x 10’ ~522 ly General Object Information NGC 7293 is known as the Helix Nebula. It is also catalogued as Caldwell 63. It is one of the largest examples of a planetary nebula visible in amateur telescopes. Its true size is 1.5 x 1.2 ly. It is located 11° north west of Pisces Austrini (Fomalhaut). It was discovered ~1874 by Friedrich von Auwers It is bright at ~ 6th magnitude, but it's light is spread over a large area, giving it a low surface brightness which can make it reasonably dim in the telescope eyepiece. In addition, there is a big hole in the middle which causes many people to miss it. It is easily visible in binoculars and finder scopes and more so, with an OIII or UHC filter attached to the objective of the instrument. A low power view with binoculars or the telescope reveals the annular nature of the object. It makes a fine photographic target and is one of the most photographed of all targets. It has been the subject of some Hubble Space Telescope images that have revealed gaseous knots with comet-like tails at the inner edge of the annulus. There are a number of field stars involved with this object and the mag 13.4 central star should be visible in mid to large apertures using medium to high power. The brightness of the nebulosity is not even around the annulus. It is brighter in the north-east and south-west sections. The nebula responds well to narrowband filters, in particular the OIII type. A hand full of observers, including O’Meara, have been able to observe this target naked eye from high quality observing sites, with good altitude. NGC 7009 (The Saturn Nebula) Credit: Bruce Balick (University of Washington), Jason Alexander (University of Washington), Arsen Hajian (U.S. Naval Observatory), Yervant Terzian (Cornell University), Mario Perinotto (University of Florence, Italy), Patrizio Patriarchi (Arcetri Observatory, Italy), NASA/ESA Const: Type: Visual Mag: RA: DEC: Diameter: Distance: Aquarius Planetary Nebula 8.0 21h 4’ 11” -11° 21’ 49” .7’ x .4’ ~1,400 ly General Object Information NGC 7009 is known as the Saturn Nebula. It is also catalogued as Caldwell 55. It is one of the brightest planetary nebula at Mag 8.0. It is located 1.25° due west of Nu Aquarii, 3° from the Capricornus border. It was discovered in 1782 by William Herschel. It is easily visible in small telescopes but requires a telescope of about 10” aperture to begin detection of the nebulous extended lobes. Unlike most planetary nebula, the central star is visible in smaller telescopes. It is located in the centre of a bright elliptical bubble and shines at Mag 11.5 Hubble Space Telescope images have revealed gaseous knots at each end joined to the cavity within the bubble of gas. Deep photographs of this nebula are giving researchers a good insight into how a one solar mass star transforms into a white dwarf. This planetary shows distinct colour when observed in amateur telescopes. Some see it as green. Many see it as blue. M33 (Pinwheel or Triangulum Galaxy) Image Credit: Giovanni Benintende Const: Type: Visual Mag: RA: DEC: Diameter: Distance: Triangulum Spiral Galaxy 5.7 1h 33’ 50.8’ +30° 39’ 37 71’ x 42’ ~2.3 million ly General Object Information M33 is known as The Pinwheel Galaxy. It is also catalogued as NGC 598. It was discovered in 1764 by Messier. It is located 4° west northwest of Alpha Trianguli. M33 is a member of the local group of galaxies. It is 50,000 ly in diameter, making it about 1/3rd the size of M31. It has about 1/15th the mass of M31 or 1/7th the mass of the Milky Way. M33 may be a satellite galaxy of M31. M33 is easily observed in small to medium power binoculars, which are a good instrument to observe it with, due to its large angular size of over 1° . Outside of the Magellanic Clouds, M33 is the easiest of all galaxies to resolve. A modest aperture at low power will reveal the clockwise sweeping spiral arms. A 10” or larger telescope, under dark clear skies, will reveal several of the embedded nebulae and their associated stellar regions. An interesting challenge for small telescopes (under 6”) is to observe NGC 604. This is a massive HII region within M33. It is located 12’ northeast of the nucleus and 1’ northwest of a 10.5 magnitude star. NGC 604 has been observed in 3” refractors from high altitude northern hemisphere locations. It should be fairly easy in any telescope of 8” or larger aperture. This is a very difficult naked eye target and the naked eye observing challenge for IISAC 2009. I have observed it on a couple of occasions naked eye from Coonabarabran under exceptional conditions. What makes it a very difficult naked eye target from the Southern Hemisphere is its low altitude. Our skies are certainly dark and clear enough to see it. M33 (Pinwheel or Triangulum Galaxy) M31 (Andromeda Galaxy) Image Credit: Tony Hallas Const: Type: Visual Mag: RA: DEC: Diameter: Distance: Andromeda Spiral Galaxy 3.4 0h 42’ 44” 41°16’ 6” 190’ x 62’ ~2.3 million ly General Object Information M31 is known as The Andromeda Galaxy. It is also catalogued as NGC 224. It was discovered in the 10th century by the Persian Astronomer Alsufi. It is located 1° west of Mag 4.5 Nu Andromadae in the Chained Maiden’s Belt. M31 is a member of the local group of galaxies. It is 130,000 ly in diameter and contains 300 billion suns. It is easily the largest galaxy in the local group and has twice the mass of our own milky way. The stars in the nucleus of M31 are so tightly packed it is thought that a black hole resides at the heart of the nucleus M31 is easily observed in small to medium power binoculars, which are a good instrument to observe it with, due to its large angular size of over 3° in length. M31’s two neighbouring satellite galaxies (M32 and M110) are easily observed in small telescopes, where they appear as featureless fuzzy glows. In binoculars M32 and M110 appear stellar. M31 is a very easy galaxy to resolve in small instruments. Numerous nebulous regions and about 10 globular clusters can be resolved in 6” or larger telescopes. A 10” or larger telescope, under dark clear skies, will reveal several of the embedded nebulae and their associated stellar regions. An interesting challenge for medium telescopes (under 10”) is to observe NGC 206. This is a massive star cloud close to the galaxy’s southwestern edge. M31 is an easy naked eye target under regional skies. M31 (Andromeda Galaxy) NGC 253 (Silver Coin Galaxy) Image Credit: National Optical Astronomy Observatory (NOAO) Const: Type: Visual Mag: RA: DEC: Diameter: Distance: Sculptor Mixed Spiral Galaxy 7.3 0h 47’ 33” - 25°17’ 15” 29’ x 7’ ~9.8 million ly General Object Information NGC 253 is known as The Silver Coin Galaxy. It is also catalogued as Caldwell 65. It was discovered in 1783 by Caroline Herschel. It is located 2° northwest of the South Galactic Pole and 7.5° south southeast of Beta Ceti. NGC 253 is a member of the Sculptor group of galaxies which is the closest system to our own local group of galaxies. It is 54,000 ly in diameter and contains 75 billion suns. It is 2.5 times smaller and 4 times less massive than M31. NGC 253 is a starburst galaxy, which means its nucleus is hosting rapid and massive bursts of star birth. Each massive outburst creates a “superwind” which ejects vast amounts of energy and mass streaming into the intergalactic medium in large arcs and loops. Some of these features are 1,000 light years long. Midinfrared studies have shown the nucleus to be unusually luminous and to contain a super cluster of stars, in addition to a diffuse envelope containing an older population of supernova remnants and low mass stars. NGC 253 is an easy galaxy to resolve in medium instruments. An 8” telescope at high power will begin to show a lot of detail in the nucleus as well as the multitude of dust clouds in the arms. NGC 253 is easily observed in small to medium power binoculars, although no detail is visible. NGC 253 has been observed by several observers naked eye, including O’Meara, but is an exceptionally challenging naked eye target. It is possibly beyond the normal observing conditions of the Hunter Valley. Gamma Delphinus Image Credit: Sky and Telescope Magazine Const: Type: Visual Mag: Separation: PA: RA: DEC: Distance: Delphinus Double Star 3.9 9.1” 265° 20h 46’ 39” 16° 7’ 25” ~100 ly General Object Information Gamma Delphinus is catalogued as HR 7948, HIP 102532 and SAO 106476. It presents a lovely colour contrast, with a Mag 3.9 yellow primary accompanied by a Mag 5.3 pale yellow/white Secondary. Separation is currently 9.1" making it easy to separate in the smallest telescopes. Separation has decreased slightly from 12.0" since the first measures in 1755 to its current separation of 9.1". The position angle (PA) of the secondary has also decreased slightly over the same time period from 280º to its current position of 265º. The stars have similar proper motions and are believed to form a long period system. Both stars are of a similar apparent size with the primary being slightly larger and brighter than the secondary. Different observers see the secondary as different colours. The colours I have mentioned previously, Yellow and Pale Yellow/White are consistent with the spectral types, sometimes I see the secondary as having a pale green or emerald tone to it, depending on conditions. This is a showpiece double star in any size telescopes. Beta Cygni (Albireo) Image Credit: Centre for Astrophysics and Space Astronomy – University of Colorado Const: Type: Visual Mag: Separation: PA: RA: DEC: Distance: Cygnus Double Star 3.1 34.4” 54° 19h 30’ 43” 27° 57’ 35” ~390 ly General Object Information Albireo is catalogued as HR 7417, HIP 95947 and SAO 87301. It presents a lovely colour contrast, with a Mag 3.1 yellow/gold primary accompanied by a Mag 5.4 electric blue secondary. Separation is currently 34.4" making it easy to separate in the smallest telescopes or good binoculars. This double is set against the Cygnus Star Cloud, which makes a wonderful backdrop. Separation and PA have remained essentially unchanged since the first measures by F Struve in 1832. The stars have like proper motions and are believed to be in orbit and form a long period binary system. The primary itself was found to be a close binary pair in 1977 using speckle interferometry. It has a separation of .39” and the magnitude difference is 1.5. It was observed visually in 1979 by C. E. Worley using a 26” refractor. The pair should be observable in amateur telescopes over 25” aperture, in excellent seeing conditions. The colours I have mentioned previously, yellow and blue are consistent with the spectral types. This is one of the most celebrated, if not the most celebrated and renowned double stars in the sky. It is a showpiece double star in any size telescope. Theta Eridani (Acamar) Image Credit: Unknown Source Const: Type: Visual Mag: Separation: PA: RA: DEC: Distance: Eridanus Double Star 2.9 8.3” 90° 2h 58’ 16” - 40° 18’ 17” ~ 160 ly General Object Information Acamar is catalogued as HR 897, HIP 13847 and SAO 216113. It was described by Hartung as one of the gems of the Southern Sky. I tend to agree with him. It is one of my all time favourites. The primary is a pale blue/white star of magnitude 3.2, spectral type A4III (pale blue to white giant), with the secondary another pale blue/white star magnitude 4.1, of spectral type A1V (pale blue dwarf) at position angle 90° with an angular separation of 8.3”. I see both stars as pale blue/white in my 10” reflector, which is consistent with their spectral types. This does not always occur with visual observations of double stars. Some observers see the colours as being more white than blue, while some observers have described both stars as having a yellowish tinge. The apparent visual colour of stars can of course be aperture dependant. Since John Hershel’s original measurements in 1835, the only change has been slow direct motion. The stars form a long period system. An excellent double star for any size telescope.