NGC 654 is an open cluster in the constellation Cassiopeia. It was discovered by William Herschel in 1787. With apparent magnitude 6.5, it can be observed by binoculars. It is located 2,5° northeast of the star Delta Cassiopeiae. In the same low power field can be seen the open clusters NGC 663 and NGC 659, it surrounds a 7th magnitude yellowish star, an F5Ia supergiant, a possible member of the group. It is 2,400 parsec away, it is a young cluster, with age 15 million years, but it can be as old as 40 million years, with a time spread of star formation of at least ∼20 Myr. The central region of the cluster shows less reddering than the rest of the cluster. An explanation given is the fact that between the solar system and the cluster lie two dust layers, one at 200pc and one more at 1Kpc. Behind the cluster is one more dust layer; the cluster has approx. 80 members. The earliest spectral type is around B0 and members of the cluster are a few luminous stars, like HD 10494, F5Ia. In the cluster have been found three Be stars.
NGC 654 is assumed to form part of the stellar association Cassiopeia OB8, located in the Perseus arm of the Milky Way, along with the open clusters M103, NGC 663, NGC 659, some supergiant stars scattered between them, all of them having similar ages and distances. NGC 654 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Sky Map and images
The Iris Nebula known as NGC 7023 and Caldwell 4, is a bright reflection nebula and Caldwell object in the constellation Cepheus. NGC 7023 is the cluster within the nebula, LBN 487, the nebula is lit by a magnitude +7 star, SAO 19158, it shines at magnitude +6.8. It is located near the Mira-type variable star T Cephei, near the bright magnitude +3.23 variable star Beta Cephei. It is six light-years across. Pasachoff, Jay M.. "Atlas of the Sky". Stars and Planets. New York, New York: Peterson Field Guides. Pp. 578 pg. ISBN 978-0-395-93432-6. Caldwell-Moore, Sir Patrick. Firefly Atlas of the Universe. Firefly Books Limited. ISBN 978-1-55297-819-1. "NGC 7023". SIMBAD. Centre de données astronomiques de Strasbourg. SEDS – NGC 7023 VizieR – NGC 7023 NED – NGC 7023 Dark Atmospheres Photography – Iris Nebula NGC 7023 See NGC 7023 in WorldWide Telescope Iris Nebula on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Sky Map and images
New General Catalogue
The New General Catalogue of Nebulae and Clusters of Stars is a catalogue of deep-sky objects compiled by John Louis Emil Dreyer in 1888. It expands upon the cataloguing work of William and Caroline Herschel, John Herschel's General Catalogue of Nebulae and Clusters of Stars; the NGC contains 7,840 objects, known as the NGC objects. It is one of the largest comprehensive catalogues, as it includes all types of deep space objects, including galaxies, star clusters, emission nebulae and absorption nebulae. Dreyer published two supplements to the NGC in 1895 and 1908, known as the Index Catalogues, describing a further 5,386 astronomical objects. Objects in the sky of the southern hemisphere are catalogued somewhat less but many were observed by John Herschel or James Dunlop; the NGC had many errors, but an attempt to eliminate them was initiated by the NGC/IC Project in 1993, after partial attempts with the Revised New General Catalogue by Jack W. Sulentic and William G. Tifft in 1973, NGC2000.0 by Roger W. Sinnott in 1988.
The Revised New General Catalogue and Index Catalogue was compiled in 2009 by Wolfgang Steinicke. The original New General Catalogue was compiled during the 1880s by John Louis Emil Dreyer using observations from William Herschel and his son John, among others. Dreyer had published a supplement to Herschel's General Catalogue of Nebulae and Clusters, containing about 1,000 new objects. In 1886, he suggested building a second supplement to the General Catalogue, but the Royal Astronomical Society asked Dreyer to compile a new version instead; this led to the publication of the New General Catalogue in the Memoirs of the Royal Astronomical Society in 1888. Assembling the NGC was a challenge, as Dreyer had to deal with many contradicting and unclear reports, made with a variety of telescopes with apertures ranging from 2 to 72 inches. While he did check some himself, the sheer number of objects meant Dreyer had to accept them as published by others for the purpose of his compilation; the catalogue contained several errors relating to position and descriptions, but Dreyer referenced the catalogue, which allowed astronomers to review the original references and publish corrections to the original NGC.
The first major update to the NGC is the Index Catalogue of Nebulae and Clusters of Stars, published in two parts by Dreyer in 1895 and 1908. It serves as a supplement to the NGC, contains an additional 5,386 objects, collectively known as the IC objects, it summarizes the discoveries of galaxies and nebulae between 1888 and 1907, most of them made possible by photography. A list of corrections to the IC was published in 1912; the Revised New Catalogue of Nonstellar Astronomical Objects was compiled by Jack W. Sulentic and William G. Tifft in the early 1970s, was published in 1973, as an update to the NGC; the work did not incorporate several previously-published corrections to the NGC data, introduced some new errors. Nearly 800 objects are listed as "non-existent" in the RNGC; the designation is applied to objects which are duplicate catalogue entries, those which were not detected in subsequent observations, a number of objects catalogued as star clusters which in subsequent studies were regarded as coincidental groupings.
A 1993 monograph considered the 229 star clusters called non-existent in the RNGC. They had been "misidentified or have not been located since their discovery in the 18th and 19th centuries", it found that one of the 229—NGC 1498—was not in the sky. Five others were duplicates of other entries, 99 existed "in some form", the other 124 required additional research to resolve; as another example, reflection nebula NGC 2163 in Orion was classified "non-existent" due to a transcription error by Dreyer. Dreyer corrected his own mistake in the Index Catalogues, but the RNGC preserved the original error, additionally reversed the sign of the declination, resulting in NGC 2163 being classified as non-existent. NGC 2000.0 is a 1988 compilation of the NGC and IC made by Roger W. Sinnott, using the J2000.0 coordinates. It incorporates several errata made by astronomers over the years; the NGC/IC Project is a collaboration formed in 1993. It aims to identify all NGC and IC objects, collect images and basic astronomical data on them.
The Revised New General Catalogue and Index Catalogue is a compilation made by Wolfgang Steinicke in 2009. It is a authoritative treatment of the NGC and IC catalogues. Messier object Catalogue of Nebulae and Clusters of Stars Astronomical catalogue List of astronomical catalogues List of NGC objects The Interactive NGC Catalog Online Adventures in Deep Space: Challenging Observing Projects for Amateur Astronomers. Revised New General Catalogue
An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy, many more are thought to exist, they are loosely bound by mutual gravitational attraction and become disrupted by close encounters with other clusters and clouds of gas as they orbit the galactic center. This can result in a migration to the main body of the galaxy and a loss of cluster members through internal close encounters. Open clusters survive for a few hundred million years, with the most massive ones surviving for a few billion years. In contrast, the more massive globular clusters of stars exert a stronger gravitational attraction on their members, can survive for longer. Open clusters have been found only in spiral and irregular galaxies, in which active star formation is occurring. Young open clusters may be contained within the molecular cloud from which they formed, illuminating it to create an H II region.
Over time, radiation pressure from the cluster will disperse the molecular cloud. About 10% of the mass of a gas cloud will coalesce into stars before radiation pressure drives the rest of the gas away. Open clusters are key objects in the study of stellar evolution; because the cluster members are of similar age and chemical composition, their properties are more determined than they are for isolated stars. A number of open clusters, such as the Pleiades, Hyades or the Alpha Persei Cluster are visible with the naked eye; some others, such as the Double Cluster, are perceptible without instruments, while many more can be seen using binoculars or telescopes. The Wild Duck Cluster, M11, is an example; the prominent open cluster the Pleiades has been recognized as a group of stars since antiquity, while the Hyades forms part of Taurus, one of the oldest constellations. Other open clusters were noted by early astronomers as unresolved fuzzy patches of light; the Roman astronomer Ptolemy mentions the Praesepe, the Double Cluster in Perseus, the Ptolemy Cluster, while the Persian astronomer Al-Sufi wrote of the Omicron Velorum cluster.
However, it would require the invention of the telescope to resolve these nebulae into their constituent stars. Indeed, in 1603 Johann Bayer gave three of these clusters designations; the first person to use a telescope to observe the night sky and record his observations was the Italian scientist Galileo Galilei in 1609. When he turned the telescope toward some of the nebulous patches recorded by Ptolemy, he found they were not a single star, but groupings of many stars. For Praesepe, he found more than 40 stars. Where observers had noted only 6-7 stars in the Pleiades, he found 50. In his 1610 treatise Sidereus Nuncius, Galileo Galilei wrote, "the galaxy is nothing else but a mass of innumerable stars planted together in clusters." Influenced by Galileo's work, the Sicilian astronomer Giovanni Hodierna became the first astronomer to use a telescope to find undiscovered open clusters. In 1654, he identified the objects now designated Messier 41, Messier 47, NGC 2362 and NGC 2451, it was realised as early as 1767 that the stars in a cluster were physically related, when the English naturalist Reverend John Michell calculated that the probability of just one group of stars like the Pleiades being the result of a chance alignment as seen from Earth was just 1 in 496,000.
Between 1774–1781, French astronomer Charles Messier published a catalogue of celestial objects that had a nebulous appearance similar to comets. This catalogue included 26 open clusters. In the 1790s, English astronomer William Herschel began an extensive study of nebulous celestial objects, he discovered. Herschel conceived the idea that stars were scattered across space, but became clustered together as star systems because of gravitational attraction, he divided the nebulae into eight classes, with classes VI through VIII being used to classify clusters of stars. The number of clusters known continued to increase under the efforts of astronomers. Hundreds of open clusters were listed in the New General Catalogue, first published in 1888 by the Danish-Irish astronomer J. L. E. Dreyer, the two supplemental Index Catalogues, published in 1896 and 1905. Telescopic observations revealed two distinct types of clusters, one of which contained thousands of stars in a regular spherical distribution and was found all across the sky but preferentially towards the centre of the Milky Way.
The other type consisted of a sparser population of stars in a more irregular shape. These were found in or near the galactic plane of the Milky Way. Astronomers dubbed the former globular clusters, the latter open clusters; because of their location, open clusters are referred to as galactic clusters, a term, introduced in 1925 by the Swiss-American astronomer Robert Julius Trumpler. Micrometer measurements of the positions of stars in clusters were made as early as 1877 by the German astronomer E. Schönfeld and further pursued by the American astronomer E. E. Barnard prior to his death in 1923. No indication of stellar motion was detected by these efforts. However, in 1918 the Dutch-American astronomer Adriaan van Maanen was able to measure the proper motion of stars in part of the Pleiades cluster by comparing photographic plates taken at different times; as astrometry became more accurate, cluster stars were found to share a common proper motion through space. By comparing the photographic plates of the Pleiades cluster taken in 1918 with images taken in 1943, van
The parsec is a unit of length used to measure large distances to astronomical objects outside the Solar System. A parsec is defined as the distance at which one astronomical unit subtends an angle of one arcsecond, which corresponds to 648000/π astronomical units. One parsec is equal to 31 trillion kilometres or 19 trillion miles; the nearest star, Proxima Centauri, is about 1.3 parsecs from the Sun. Most of the stars visible to the unaided eye in the night sky are within 500 parsecs of the Sun; the parsec unit was first suggested in 1913 by the British astronomer Herbert Hall Turner. Named as a portmanteau of the parallax of one arcsecond, it was defined to make calculations of astronomical distances from only their raw observational data quick and easy for astronomers. For this reason, it is the unit preferred in astronomy and astrophysics, though the light-year remains prominent in popular science texts and common usage. Although parsecs are used for the shorter distances within the Milky Way, multiples of parsecs are required for the larger scales in the universe, including kiloparsecs for the more distant objects within and around the Milky Way, megaparsecs for mid-distance galaxies, gigaparsecs for many quasars and the most distant galaxies.
In August 2015, the IAU passed Resolution B2, which, as part of the definition of a standardized absolute and apparent bolometric magnitude scale, mentioned an existing explicit definition of the parsec as 648000/π astronomical units, or 3.08567758149137×1016 metres. This corresponds to the small-angle definition of the parsec found in many contemporary astronomical references; the parsec is defined as being equal to the length of the longer leg of an elongated imaginary right triangle in space. The two dimensions on which this triangle is based are its shorter leg, of length one astronomical unit, the subtended angle of the vertex opposite that leg, measuring one arc second. Applying the rules of trigonometry to these two values, the unit length of the other leg of the triangle can be derived. One of the oldest methods used by astronomers to calculate the distance to a star is to record the difference in angle between two measurements of the position of the star in the sky; the first measurement is taken from the Earth on one side of the Sun, the second is taken half a year when the Earth is on the opposite side of the Sun.
The distance between the two positions of the Earth when the two measurements were taken is twice the distance between the Earth and the Sun. The difference in angle between the two measurements is twice the parallax angle, formed by lines from the Sun and Earth to the star at the distant vertex; the distance to the star could be calculated using trigonometry. The first successful published direct measurements of an object at interstellar distances were undertaken by German astronomer Friedrich Wilhelm Bessel in 1838, who used this approach to calculate the 3.5-parsec distance of 61 Cygni. The parallax of a star is defined as half of the angular distance that a star appears to move relative to the celestial sphere as Earth orbits the Sun. Equivalently, it is the subtended angle, from that star's perspective, of the semimajor axis of the Earth's orbit; the star, the Sun and the Earth form the corners of an imaginary right triangle in space: the right angle is the corner at the Sun, the corner at the star is the parallax angle.
The length of the opposite side to the parallax angle is the distance from the Earth to the Sun (defined as one astronomical unit, the length of the adjacent side gives the distance from the sun to the star. Therefore, given a measurement of the parallax angle, along with the rules of trigonometry, the distance from the Sun to the star can be found. A parsec is defined as the length of the side adjacent to the vertex occupied by a star whose parallax angle is one arcsecond; the use of the parsec as a unit of distance follows from Bessel's method, because the distance in parsecs can be computed as the reciprocal of the parallax angle in arcseconds. No trigonometric functions are required in this relationship because the small angles involved mean that the approximate solution of the skinny triangle can be applied. Though it may have been used before, the term parsec was first mentioned in an astronomical publication in 1913. Astronomer Royal Frank Watson Dyson expressed his concern for the need of a name for that unit of distance.
He proposed the name astron, but mentioned that Carl Charlier had suggested siriometer and Herbert Hall Turner had proposed parsec. It was Turner's proposal. In the diagram above, S represents the Sun, E the Earth at one point in its orbit, thus the distance ES is one astronomical unit. The angle SDE is one arcsecond so by definition D is a point in space at a distance of one parsec from the Sun. Through trigonometry, the distance SD is calculated as follows: S D = E S tan 1 ″ S D ≈ E S 1 ″ = 1 au 1 60 × 60 × π
Astronomical Society of the Pacific
The Astronomical Society of the Pacific is an American scientific and educational organization, founded in San Francisco on February 7, 1889. Its name derives from its origins on the Pacific Coast, but today it has members all over the country and the world, it has the legal status of a nonprofit organization. It is the largest general astronomy education society in the world, with members from over 40 countries; the ASP's goal is to promote public interest in and awareness of astronomy through its publications, web site, many educational and outreach programs. These include: Project ASTRO - a national program that improves the teaching of astronomy and physical science by pairing amateur and professional astronomers with 4th through 9th grade teachers and classes. Family ASTRO - a project that develops kits and games to help families enjoy astronomy in their leisure time and trains astronomers and community leaders Astronomy from the Ground Up - a national program to help educators at smaller science museums, nature centers and environmental education organizations create or enhance astronomy education programs.
The Night Sky Network - a program with the Jet Propulsion Laboratory that supports a community of over 450 amateur astronomy clubs around the U. S. in public outreach activities, providing them with kits and training. The clubs have sky gazing events, solar viewings, give presentations for the public. Classroom materials and resources in astronomy sold through their online AstroShop or made available free through their web siteThe ASP assists with astronomy education and outreach by partnering with other organizations both in the United States and internationally, organizes an annual meeting to promote the appreciation and understanding of astronomy. Presidents of the ASP have included such notable astronomers as Edwin Hubble, George O. Abell, Frank Drake. George Pardee, who became Governor of the State of California, served as president in 1899; the society promotes astronomy education through several publications. The Universe in the Classroom, a free electronic educational newsletter for teachers and other educators around the world who help students of all ages learn more about the wonders of the universe through astronomy.
Mercury, the ASP's quarterly on-line membership magazine, covers a wide range of astronomy topics, from history and archaeoastronomy to cutting-edge developments. First published in 1925 as the Leaflets of the ASP, Mercury is now disseminated to thousands of ASP members and schools, libraries and institutions around the world; the ASP publishes the journal Publications of the Astronomical Society of the Pacific aimed at professional astronomers. The PASP is a technical journal of refereed papers on astronomical research covering all wavelengths and distance scales as well as papers on the latest innovations in astronomical instrumentation and software, has been publishing journals since 1889; the Astronomical Society of the Pacific Conference Series is a series of over 400 volumes of professional astronomy conference proceedings. Started in 1988, the Conference Series has grown to become a prominent publication series in the world of professional astronomy publications, now publishes an average of 20-25 volumes per year.
Volumes are sold to the attendees of the conferences of which the proceedings are published, as well as being offered through the Astronomical Society of the Pacific's AstroShop, can be found in the libraries of major universities and research institutions worldwide. In 2004, the ASPCS stepped into electronic publishing, offering electronic access subscriptions for libraries and institutions, as well as individual access to volumes which they have purchased in hard copy form. Astronomy Beat is an on-line column, which comes out every other week, features a behind-the-scenes report on some aspect of astronomical discovery, astronomy education, or astronomy as a hobby, written by a key participant. Authors have included: Clyde Tombaugh, retelling the story of his discovery of the planet Pluto Michael E. Brown, discussing the naming of the dwarf planet Makemake Noted astronomical photographer David Malin describing the transition from chemical to digital photography Virginia Louise Trimble explaining how she selected her list of the top ten astronomical discoveries of the last thousand years.
The ASP makes several different awards annually: The Bruce Medal for lifetime contribution to astronomy research. The medal is named after Catherine Wolfe Bruce; this award is arguably the most prestigious award given in astronomy. The Klumpke-Roberts Award for outstanding contributions to the public understanding and appreciation of astronomy, named for Dorothea Klumpke-Roberts; the Amateur Achievement Award in recognition of significant contributions to astronomy by one not employed in the field of astronomy in a professional capacity. The Bart Bok Award, named in honor of astronomer Bart Bok, awarded jointly with the American Astronomical Society to outstanding student projects in astronomy at the International Science and Engineering Fair; the Thomas Brennan Award for exceptional achievement related to the teaching of astronomy at the high school level. The Maria and Eric Muhlmann Award for recent significant observational results made possible by innovative advances in astronomical instrumentation, software, or observational infrastructure.
The Robert J. Trumpler Award, named in honor of astronomer Robert J. Trumpler, given to a recent recipient of a Ph. D degree with a notable thesis; the Richard Emmons Award is given for a lifetime of contributions to the teaching of astronomy to college non-s
The Astronomical Journal
The Astronomical Journal is a peer-reviewed monthly scientific journal owned by the American Astronomical Society and published by IOP Publishing. It is one of the premier journals for astronomy in the world; until 2008, the journal was published by the University of Chicago Press on behalf of the American Astronomical Society. The reasons for the change were given by the society as the desire of the University of Chicago Press to revise its financial arrangement and their plans to change from the particular software, developed in-house; the other two publications of the society, the Astrophysical Journal and its supplement series, followed in January 2009. The journal was established in 1849 by Benjamin A. Gould, it ceased publication in 1861 due to the American Civil War, but resumed in 1885. Between 1909 and 1941 the journal was edited in New York. In 1941, editor Benjamin Boss arranged to transfer responsibility for the journal to the American Astronomical Society; the first electronic edition of The Astronomical Journal was published in January, 1998.
With the July, 2006 issue, The Astronomical Journal began e-first publication, an electronic version of the journal released independently of the hardcopy issues. 2005–2015 John Gallagher III 1984–2004 Paul W. Hodge 1980–1983 N. H. Baker 1975–1979 N. H. Baker and L. B. Lucy 1967–1974 Lodewijk Woltjer 1966–1967 Gerald Maurice Clemence 1965–1966 Dirk Brouwer and Gerald Maurice Clemence 1963–1965 Dirk Brouwer 1959–1963 Dirk Brouwer and Harlan James Smith 1941–1959 Dirk Brouwer 1912–1941 Benjamin Boss 1909–1912 Lewis Boss 1896–1909 Seth Carlo Chandler 1849–1861, 1885–1896 Benjamin A. Gould, Jr; the Astronomical Almanac The Astrophysical Journal Official website Dudley Observatory, The Astronomical Journal Scanned issues from ADS