difference between ngc and m ( messier )
difference between ngc and m ( messier )
i know this is a stupid question but i've seen it so many times and ive searched nonstop for the answers but failed... just what is the difference betweetn the both ? for example... ngc 1981 , an open cluster in orion and m42 , the orion nebula.
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Airconvent
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Re: difference between ngc and m ( messier )
without going into too much unnecessary details, they are both 2 different catalogs.fiona_ wrote:i know this is a stupid question but i've seen it so many times and ive searched nonstop for the answers but failed... just what is the difference betweetn the both ? for example... ngc 1981 , an open cluster in orion and m42 , the orion nebula.
Charles Messier was a french who was interested in searching for comets. To avoid mistaking "unwanted" objects as comets , he created a list of these items in no particular order. These includes some of the brightest DSOs and eventually, this list was used by astronomers as a common reference guide. It became known as the Messier list or "M" for short.
Some minor additions were made to the list and it is now 110-long (if memory serves), hence M1 to M110.
The NGC (New General Catalog) is much more extensive , covering a wider range of objects. There are also other list such as the Caldwell list which is a list of favourite objects selected by renowned british astronomer Patrick Moore.
rich
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weixing
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Hi,
Below are some history of NGC taken from the web:
Dreyer was born in Denmark, but emigrated to Ireland in 1874 to work at Lord Rosse's great observatory in Parsonstown. Though an amateur, the third Earl of Rosse had built successively larger speculum mirror reflecting telescopes through the late 1830's and early 1840's. The series culminated in a massive 72-inch telescope, the largest in the world from the date of its completion in 1845 until its dismantling just before the first World War. Rosse, his son (the fourth earl), and his observers (Dreyer was one of these) spent years examining and measuring the known nebulae in the northern sky with the famous "Leviathan of Parsonstown," and discovered many more fainter nebulae themselves.
During the observations, it became clear to Dreyer that it was time to update Sir John Herschel's so-called GC (General Catalogue) of nebulae and star clusters, published in 1864. Just a decade later, there were simply too many new nebulae being discovered and too many different lists to consult for previous discoveries. Preparing observing lists or simply finding if a nebula had been previously found by another observer had become a time-consuming chore. Thus, Dreyer published a supplement to the GC of about 1000 new objects in 1878, and -- having suggested yet another supplement in 1886 -- was instead asked by the Royal Astronomical Society to assemble a "new general catalogue" of non-stellar objects. So, Dreyer added the latest 1500 objects to the previous lists, combined them all in Right Ascension (for 1860) order, and the "New General Catalogue of Nebulae and Star Clusters" appeared as Volume 49, Number 1 of the Memoirs of the RAS in 1888.
Assembling the NGC, Dreyer had to contend with conflicting claims of position and description for what he often suspected to be the same nebula. Some of these he could check himself; most -- because of the overwhelming numbers of objects -- he simply had to accept as published. Fortunately, he was an excellent transcriber -- very few of the errors in the NGC can be traced to carelessness on his part (his most common error, or that of his uncredited assistants, was to apply precession with the wrong sign to declinations). Most of the problems in the NGC are with the original positions and descriptions, coming as they did from many different observers using telescopes ranging in size from 2 inches to 72 inches, and relying on auxiliary instrumentation that ranged from nonexistent to state of the art.
At one extreme were the careful observations of the astrometrists working at professional observatories. These observers were actively involved not only in nebular astronomy -- indeed, with one or two exceptions, the nebulae consumed very little of their time and attention -- but in setting up the fundamental coordinate reference system which we still use today in a form little different than it was a century ago. These observations, made with precision optical micrometers, tie the positions of the nebulae into the fundamental system with random errors on the order of a few tenths of an arc-second. Only in the past two decades have better positions for a significant number of galaxies been determined from plates taken with astrographic telescopes.
On the other hand, there were many amateur and semiprofessional astronomers actively making discoveries. Some of these observers were well-equipped with large, solidly-mounted telescopes fitted out with modern instrumentation. Some, like Isaac Roberts, were even at the forefront of astronomical photography. Others were neither as fortunate in their observing gear, nor as careful in their observing habits. Many scanned the skies with nothing more than an eyepiece and setting circles at their disposal. Yet, they published their discoveries along side those from the professional observatories. Dreyer had to handle them all.
Thus, the NGC is a compendium of the good and the not so good. Through long experience and comparison of lists of positions from various observers, Dreyer had a good idea whose observations were trustworthy, and whose were not. He also realized the importance of not letting this information be lost (as well as simply giving credit where it's due!), so he listed the discoverers of each nebula and star cluster, and gave fairly complete references to the discovery publications. These references are our key today to unraveling the problems in the catalogues.
Hope the above information is useful.
Below are some history of NGC taken from the web:
Dreyer was born in Denmark, but emigrated to Ireland in 1874 to work at Lord Rosse's great observatory in Parsonstown. Though an amateur, the third Earl of Rosse had built successively larger speculum mirror reflecting telescopes through the late 1830's and early 1840's. The series culminated in a massive 72-inch telescope, the largest in the world from the date of its completion in 1845 until its dismantling just before the first World War. Rosse, his son (the fourth earl), and his observers (Dreyer was one of these) spent years examining and measuring the known nebulae in the northern sky with the famous "Leviathan of Parsonstown," and discovered many more fainter nebulae themselves.
During the observations, it became clear to Dreyer that it was time to update Sir John Herschel's so-called GC (General Catalogue) of nebulae and star clusters, published in 1864. Just a decade later, there were simply too many new nebulae being discovered and too many different lists to consult for previous discoveries. Preparing observing lists or simply finding if a nebula had been previously found by another observer had become a time-consuming chore. Thus, Dreyer published a supplement to the GC of about 1000 new objects in 1878, and -- having suggested yet another supplement in 1886 -- was instead asked by the Royal Astronomical Society to assemble a "new general catalogue" of non-stellar objects. So, Dreyer added the latest 1500 objects to the previous lists, combined them all in Right Ascension (for 1860) order, and the "New General Catalogue of Nebulae and Star Clusters" appeared as Volume 49, Number 1 of the Memoirs of the RAS in 1888.
Assembling the NGC, Dreyer had to contend with conflicting claims of position and description for what he often suspected to be the same nebula. Some of these he could check himself; most -- because of the overwhelming numbers of objects -- he simply had to accept as published. Fortunately, he was an excellent transcriber -- very few of the errors in the NGC can be traced to carelessness on his part (his most common error, or that of his uncredited assistants, was to apply precession with the wrong sign to declinations). Most of the problems in the NGC are with the original positions and descriptions, coming as they did from many different observers using telescopes ranging in size from 2 inches to 72 inches, and relying on auxiliary instrumentation that ranged from nonexistent to state of the art.
At one extreme were the careful observations of the astrometrists working at professional observatories. These observers were actively involved not only in nebular astronomy -- indeed, with one or two exceptions, the nebulae consumed very little of their time and attention -- but in setting up the fundamental coordinate reference system which we still use today in a form little different than it was a century ago. These observations, made with precision optical micrometers, tie the positions of the nebulae into the fundamental system with random errors on the order of a few tenths of an arc-second. Only in the past two decades have better positions for a significant number of galaxies been determined from plates taken with astrographic telescopes.
On the other hand, there were many amateur and semiprofessional astronomers actively making discoveries. Some of these observers were well-equipped with large, solidly-mounted telescopes fitted out with modern instrumentation. Some, like Isaac Roberts, were even at the forefront of astronomical photography. Others were neither as fortunate in their observing gear, nor as careful in their observing habits. Many scanned the skies with nothing more than an eyepiece and setting circles at their disposal. Yet, they published their discoveries along side those from the professional observatories. Dreyer had to handle them all.
Thus, the NGC is a compendium of the good and the not so good. Through long experience and comparison of lists of positions from various observers, Dreyer had a good idea whose observations were trustworthy, and whose were not. He also realized the importance of not letting this information be lost (as well as simply giving credit where it's due!), so he listed the discoverers of each nebula and star cluster, and gave fairly complete references to the discovery publications. These references are our key today to unraveling the problems in the catalogues.
Hope the above information is useful.
Yang Weixing
"The universe is composed mainly of hydrogen and ignorance."
"The universe is composed mainly of hydrogen and ignorance."