NGC 6578 is a planetary nebula located in Sagittarius. It is magnitude 13.5 with diameter 8 arc seconds. It has a 16th magnitude central star, it is seen near the star 16 Sagittarii. List of NGC objects Planetary nebulae Robert Burnham, Jr, Burnham's Celestial Handbook: An observer's guide to the universe beyond the solar system, vol 3, p.1557 The Hubble European Space Agency Information Centre Hubble picture and information on NGC 6578 Hubble December 17th, 1997
Wild Duck Cluster
The Wild Duck Cluster is an open cluster of stars in the southern constellation of Scutum. It was discovered by Gottfried Kirch in 1681. Charles Messier included it in his catalogue of diffuse objects in 1764, its name derives from the brighter stars forming a triangle which could resemble a flying flock of ducks. The cluster is located just to the east of the Scutum Star Cloud midpoint; the Wild Duck Cluster is one of the most compact of the known open clusters. It is one of the most massive open clusters known, it has been extensively studied, its age has been estimated to about 316 million years. The core radius is 1.23 pc. Estimates for the cluster mass range from 3,700 M☉ to 11,000 M☉, depending on the method chosen, The brightest cluster member is visual magnitude 8, it has 870 members of at least magnitude 16.5. It has an integrated absolute magnitude of –6.5, a visual extinction of 1.3. The cluster is metal-rich with an iron abundance of = 0.17±0.04. Despite its youth, it shows an enhancement of Alpha process elements.
This is due to an enhancement of its birth molecular cloud by a nearby Type II supernova explosion. At least nine variable star members have been identified with high probability, plus 29 lower probability members; the former include two eclipsing binary star systems. The cluster is located 6.8 kpc from the galactic center, close to the galactic plane, is not far from its birthplace. Messier 11, SEDS Messier pages Messier 11, Wild Duck Cluster Messier 11 - LRGB result based on 2 hrs total data The Wild Duck Cluster on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Sky Map and images
NGC 6559 is a star-forming region located at a distance of about 5000 light-years from Earth, in the constellation of Sagittarius, showing both emission and reflection regions. NASA Astronomy Picture of the Day: Three Nebular in Narrow Band - one of the three nebulae shown was NGC 6559 NASA Astronomy Picture of the Day: Stars and Nebula in NGC 6559 NGC 6559
NGC 6584 is a globular cluster in the constellation Telescopium that lies near Theta Arae and is 45000 light-years distant. It is an Oosterhoff type I cluster, contains at least 69 variable stars, most of which are RR Lyrae variables: 46 stars were identified as RRab variables, 15 as RRc variables, 1 RRe variable, 4 eclipsing binaries and 3 long period variables. NGC 6584 is about 4 kpc from the Galactic center and about 2.7 kpc from the Galactic plane
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
In physics, redshift is a phenomenon where electromagnetic radiation from an object undergoes an increase in wavelength. Whether or not the radiation is visible, "redshift" means an increase in wavelength, equivalent to a decrease in wave frequency and photon energy, in accordance with the wave and quantum theories of light. Neither the emitted nor perceived light is red. Examples of redshifting are a gamma ray perceived as an X-ray, or visible light perceived as radio waves; the opposite of a redshift is energy increases. However, redshift is a more common term and sometimes blueshift is referred to as negative redshift. There are three main causes of red in astronomy and cosmology: Objects move apart in space; this is an example of the Doppler effect. Space itself expands; this is known as cosmological redshift. All sufficiently distant light sources show redshift corresponding to the rate of increase in their distance from Earth, known as Hubble's Law. Gravitational redshift is a relativistic effect observed due to strong gravitational fields, which distort spacetime and exert a force on light and other particles.
Knowledge of redshifts and blueshifts has been used to develop several terrestrial technologies such as Doppler radar and radar guns. Redshifts are seen in the spectroscopic observations of astronomical objects, its value is represented by the letter z. A special relativistic redshift formula can be used to calculate the redshift of a nearby object when spacetime is flat. However, in many contexts, such as black holes and Big Bang cosmology, redshifts must be calculated using general relativity. Special relativistic and cosmological redshifts can be understood under the umbrella of frame transformation laws. There exist other physical processes that can lead to a shift in the frequency of electromagnetic radiation, including scattering and optical effects; the history of the subject began with the development in the 19th century of wave mechanics and the exploration of phenomena associated with the Doppler effect. The effect is named after Christian Doppler, who offered the first known physical explanation for the phenomenon in 1842.
The hypothesis was tested and confirmed for sound waves by the Dutch scientist Christophorus Buys Ballot in 1845. Doppler predicted that the phenomenon should apply to all waves, in particular suggested that the varying colors of stars could be attributed to their motion with respect to the Earth. Before this was verified, however, it was found that stellar colors were due to a star's temperature, not motion. Only was Doppler vindicated by verified redshift observations; the first Doppler redshift was described by French physicist Hippolyte Fizeau in 1848, who pointed to the shift in spectral lines seen in stars as being due to the Doppler effect. The effect is sometimes called the "Doppler–Fizeau effect". In 1868, British astronomer William Huggins was the first to determine the velocity of a star moving away from the Earth by this method. In 1871, optical redshift was confirmed when the phenomenon was observed in Fraunhofer lines using solar rotation, about 0.1 Å in the red. In 1887, Vogel and Scheiner discovered the annual Doppler effect, the yearly change in the Doppler shift of stars located near the ecliptic due to the orbital velocity of the Earth.
In 1901, Aristarkh Belopolsky verified optical redshift in the laboratory using a system of rotating mirrors. The earliest occurrence of the term red-shift in print appears to be by American astronomer Walter S. Adams in 1908, in which he mentions "Two methods of investigating that nature of the nebular red-shift"; the word does not appear unhyphenated until about 1934 by Willem de Sitter indicating that up to that point its German equivalent, was more used. Beginning with observations in 1912, Vesto Slipher discovered that most spiral galaxies mostly thought to be spiral nebulae, had considerable redshifts. Slipher first reports on his measurement in the inaugural volume of the Lowell Observatory Bulletin. Three years he wrote a review in the journal Popular Astronomy. In it he states that "the early discovery that the great Andromeda spiral had the quite exceptional velocity of –300 km showed the means available, capable of investigating not only the spectra of the spirals but their velocities as well."
Slipher reported the velocities for 15 spiral nebulae spread across the entire celestial sphere, all but three having observable "positive" velocities. Subsequently, Edwin Hubble discovered an approximate relationship between the redshifts of such "nebulae" and the distances to them with the formulation of his eponymous Hubble's law; these observations corroborated Alexander Friedmann's 1922 work, in which he derived the Friedmann-Lemaître equations. They are today considered strong evidence for the Big Bang theory; the spectrum of light that comes from a single source can be measured. To determine the redshift, one searches for features in the spectrum such as absorption lines, emission lines, or other variations in light intensity. If found, these featur
A starburst galaxy is a galaxy undergoing an exceptionally high rate of star formation, as compared to the long-term average rate of star formation in the galaxy or the star formation rate observed in most other galaxies. For example, the star formation rate of the Milky Way galaxy is 3 M☉/yr, starburst galaxies can experience star formation rates that are more than a factor of 100 times greater. In a starburst galaxy, the rate of star formation is so large that the galaxy will consume all of its gas reservoir, from which the stars are forming, on a timescale much shorter than the age of the galaxy; as such, the starburst nature of a galaxy is a phase, one that occupies a brief period of a galaxy's evolution. The majority of starburst galaxies are in the midst of a merger or close encounter with another galaxy. Starburst galaxies include M82, NGC 4038/NGC 4039, IC 10. Starburst galaxies are defined by these three interrelated factors: The rate at which the galaxy is converting gas into stars.
The available quantity of gas from which stars can be formed. A comparison of the timescale on which star formation will consume the available gas with the age or rotation period of the galaxy. Used definitions include: Continued star-formation where the current SFR would exhaust the available gas reservoir in much less than the age of the Universe. Continued star-formation where the current SFR would exhaust the available gas reservoir in much less than the dynamical timescale of the galaxy; the current SFR, normalised by the past-averaged SFR, is much greater than unity. This ratio is referred to as the "birthrate parameter". Mergers and tidal interactions between gas-rich galaxies play a large role in driving starbursts. Galaxies in the midst of a starburst show tidal tails, an indication of a close encounter with another galaxy, or are in the midst of a merger. Interactions between galaxies that do not merge can trigger unstable rotation modes, such as the bar instability, which causes gas to be funneled towards the nucleus and ignites bursts of star formation near the galactic nucleus.
It has been shown that there is a strong correlation between the lopsidedness of a galaxy and the youth of its stellar population, with more lopsided galaxies having younger central stellar populations. As lopsidedness can be caused by tidal interactions and mergers between galaxies, this result gives further evidence that mergers and tidal interactions can induce central star formation in a galaxy and drive a starburst. Classifying types of starburst galaxies is difficult since starburst galaxies do not represent a specific type in and of themselves. Starbursts can occur in disk galaxies, irregular galaxies exhibit knots of starburst spread throughout the irregular galaxy. Astronomers classify starburst galaxies based on their most distinct observational characteristics; some of the categorizations include: Blue compact galaxies. These galaxies are low mass, low metallicity, dust-free objects; because they are dust-free and contain a large number of hot, young stars, they are blue in optical and ultraviolet colours.
It was thought that BCGs were genuinely young galaxies in the process of forming their first generation of stars, thus explaining their low metal content. However, old stellar populations have been found in most BCGs, it is thought that efficient mixing may explain the apparent lack of dust and metals. Most BCGs close interactions. Well-studied BCGs include IZw18, ESO338-IG04 and Haro11. Blue compact dwarf galaxies are small compact galaxies. Green Pea galaxies are small compact galaxies resembling primordial starbursts, they were found by citizen scientists taking part in the Galaxy Zoo project. Luminous infrared galaxies. Ultra-luminous Infrared Galaxies ULIRGs); these galaxies are extremely dusty objects. The ultraviolet radiation produced by the obscured star-formation is absorbed by the dust and reradiated in the infrared spectrum at wavelengths of around 100 micrometres; this explains the extreme red colours associated with ULIRGs. It is not known for sure that the UV radiation is produced purely by star-formation, some astronomers believe ULIRGs to be powered by active galactic nuclei.
X-ray observations of many ULIRGs that penetrate the dust suggest that many starburst galaxies are double-cored systems, lending support to the hypothesis that ULIRGs are powered by star-formation triggered by major mergers. Well-studied ULIRGs include Arp 220. Hyperluminous Infrared galaxies, sometimes called Submillimeter galaxies. Wolf-Rayet galaxies, galaxies where a large portion of the bright stars are Wolf-Rayet stars; the Wolf-Rayet phase is a short-lived phase in the life of massive stars 10% of the total life-time of these stars and as such any galaxy is to contain few of these. However, because the stars are both luminous and have distinctive spectral features, it is possible to identify these stars in the spectra of entire galaxies and doing so allows good constraints to be placed on the properties of the starbursts in these galaxies. Firstly, a starburst galaxy must have a large supply of gas available to form stars; the burst itself may be triggered by a close encounter with another galaxy, a collision with another galaxy, or by another process which forces material into the centre of the galaxy.
The inside of the starburst is quite an extreme environment. The large amount