The Messier objects are a set of 110 astronomical objects cataloged by the French astronomer Charles Messier in his Catalogue des Nébuleuses et des Amas d'Étoiles. Because Messier was interested in finding only comets, he created a list of non-comet objects that frustrated his hunt for them; the compilation of this list, in collaboration with his assistant Pierre Méchain, is known as the Messier catalogue. This catalogue of objects is one of the most famous lists of astronomical objects, many Messier objects are still referenced by their Messier number; the catalogue includes some astronomical objects that can be observed from Earth's Northern Hemisphere such as deep-sky objects, a characteristic which makes the Messier objects popular targets for amateur astronomers. A preliminary version first appeared in the Memoirs of the French Academy of Sciences in 1771, the last item was added in 1966 by Kenneth Glyn Jones, based on Messier's observations; the first version of Messier's catalogue contained 45 objects and was published in 1774 in the journal of the French Academy of Sciences in Paris.
In addition to his own discoveries, this version included objects observed by other astronomers, with only 17 of the 45 objects being Messier's. By 1780 the catalogue had increased to 80 objects; the final version of the catalogue containing 103 objects was published in 1781 in the Connaissance des Temps for the year 1784. However, due to what was thought for a long time to be the incorrect addition of Messier 102, the total number remained 102. Other astronomers, using side notes in Messier's texts filled out the list up to 110 objects; the catalogue consists of a diverse range of astronomical objects, ranging from star clusters and nebulae to galaxies. For example, Messier 1 is a supernova remnant, known as the Crab Nebula, the great spiral Andromeda Galaxy is M31. Many further inclusions followed in the next century when the first addition came from Nicolas Camille Flammarion in 1921, who added Messier 104 after finding Messier's side note in his 1781 edition exemplar of the catalogue. M105 to M107 were added by Helen Sawyer Hogg in 1947, M108 and M109 by Owen Gingerich in 1960, M110 by Kenneth Glyn Jones in 1967.
The first edition of 1771 covered 45 objects numbered M1 to M45. The total list published by Messier in 1781 contained 103 objects, but the list was expanded through successive additions by other astronomers, motivated by notes in Messier's and Méchain's texts indicating that at least one of them knew of the additional objects; the first such addition came from Nicolas Camille Flammarion in 1921, who added Messier 104 after finding a note Messier made in a copy of the 1781 edition of the catalog. M105 to M107 were added by Helen Sawyer Hogg in 1947, M108 and M109 by Owen Gingerich in 1960, M110 by Kenneth Glyn Jones in 1967. M102 was observed by Méchain. Méchain concluded that this object was a re-observation of M101, though some sources suggest that the object Méchain observed was the galaxy NGC 5866 and identify that as M102. Messier's final catalogue was included in the Connaissance des Temps for 1784, the French official yearly publication of astronomical ephemerides; these objects are still known by their "Messier number" from this list.
Messier did his astronomical work at the Hôtel de Cluny, in Paris, France. The list he compiled contains only objects found in the sky area he could observe: from the north celestial pole to a celestial latitude of about −35.7°. He did not observe or list objects visible only from farther south, such as the Large and Small Magellanic Clouds; the Messier catalogue comprises nearly all the most spectacular examples of the five types of deep-sky object – diffuse nebulae, planetary nebulae, open clusters, globular clusters, galaxies – visible from European latitudes. Furthermore all of the Messier objects are among the closest to Earth in their respective classes, which makes them studied with professional class instruments that today can resolve small and visually spectacular details in them. A summary of the astrophysics of each Messier object can be found in the Concise Catalog of Deep-sky Objects. Since these objects could be observed visually with the small-aperture refracting telescope used by Messier to study the sky, they are among the brightest and thus most attractive astronomical objects observable from Earth, are popular targets for visual study and astrophotography available to modern amateur astronomers using larger aperture equipment.
In early spring, astronomers sometimes gather for "Messier marathons", when all of the objects can be viewed over a single night. Lists of astronomical objects List of Messier objects Caldwell catalogue Deep-sky object Herschel 400 Catalogue New General Catalogue SEDS Messier Database Charles Messier Charles Messier's Catalog of Nebulae and Star Clusters History of the Messier Catalog Interactive Messier Catalog Greenhawk Observatory Listing of Copyright-free Images of all Messier Objects CCD Images of Messier Objects 12 Dimensional String Messier Gallery The Messier Catalogue Merrifield, Mike. "Messier Objects". Deep Sky Videos. Brady Haran. Messier Objects at Constellation Guide
An exoplanet or extrasolar planet is a planet outside the Solar System. The first evidence of an exoplanet was not recognized as such; the first scientific detection of an exoplanet was in 1988. The first confirmed detection occurred in 1992; as of 1 April 2019, there are 4,023 confirmed planets in 3,005 systems, with 656 systems having more than one planet. There are many methods of detecting exoplanets. Transit photometry and Doppler spectroscopy have found the most, but these methods suffer from a clear observational bias favoring the detection of planets near the star. In several cases, multiple planets have been observed around a star. About 1 in 5 Sun-like stars have an "Earth-sized" planet in the habitable zone. Assuming there are 200 billion stars in the Milky Way, it can be hypothesized that there are 11 billion habitable Earth-sized planets in the Milky Way, rising to 40 billion if planets orbiting the numerous red dwarfs are included; the least massive planet known is Draugr, about twice the mass of the Moon.
The most massive planet listed on the NASA Exoplanet Archive is HR 2562 b, about 30 times the mass of Jupiter, although according to some definitions of a planet, it is too massive to be a planet and may be a brown dwarf instead. There are planets that are so near to their star that they take only a few hours to orbit and there are others so far away that they take thousands of years to orbit; some are so far out. All of the planets detected so far are within the Milky Way. Nonetheless, evidence suggests that extragalactic planets, exoplanets farther away in galaxies beyond the local Milky Way galaxy, may exist; the nearest exoplanet is Proxima Centauri b, located 4.2 light-years from Earth and orbiting Proxima Centauri, the closest star to the Sun. The discovery of exoplanets has intensified interest in the search for extraterrestrial life. There is special interest in planets that orbit in a star's habitable zone, where it is possible for liquid water, a prerequisite for life on Earth, to exist on the surface.
The study of planetary habitability considers a wide range of other factors in determining the suitability of a planet for hosting life. Besides exoplanets, there are rogue planets, which do not orbit any star; these tend to be considered as a separate category if they are gas giants, in which case they are counted as sub-brown dwarfs, like WISE 0855−0714. The rogue planets in the Milky Way number in the billions; the convention for designating exoplanets is an extension of the system used for designating multiple-star systems as adopted by the International Astronomical Union. For exoplanets orbiting a single star, the designation is formed by taking the name or, more designation of its parent star and adding a lower case letter; the first planet discovered in a system is given the designation "b" and planets are given subsequent letters. If several planets in the same system are discovered at the same time, the closest one to the star gets the next letter, followed by the other planets in order of orbital size.
A provisional IAU-sanctioned standard exists to accommodate the designation of circumbinary planets. A limited number of exoplanets have IAU-sanctioned proper names. Other naming systems exist. For centuries scientists and science fiction writers suspected that extrasolar planets existed, but there was no way of detecting them or of knowing their frequency or how similar they might be to the planets of the Solar System. Various detection claims made in the nineteenth century were rejected by astronomers; the first evidence of an exoplanet was not recognized as such. The first suspected scientific detection of an exoplanet occurred in 1988. Shortly afterwards, the first confirmed detection came in 1992, with the discovery of several terrestrial-mass planets orbiting the pulsar PSR B1257+12; the first confirmation of an exoplanet orbiting a main-sequence star was made in 1995, when a giant planet was found in a four-day orbit around the nearby star 51 Pegasi. Some exoplanets have been imaged directly by telescopes, but the vast majority have been detected through indirect methods, such as the transit method and the radial-velocity method.
In February 2018, researchers using the Chandra X-ray Observatory, combined with a planet detection technique called microlensing, found evidence of planets in a distant galaxy, stating "Some of these exoplanets are as small as the moon, while others are as massive as Jupiter. Unlike Earth, most of the exoplanets are not bound to stars, so they're wandering through space or loosely orbiting between stars. We can estimate. In the sixteenth century the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are accompanied by planets. In the eighteenth century the same possibility was mentioned by Isaac Newton in the "General Scholium" that concludes his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One."In 1952, more than 40 years before the first hot Jupiter was discovere
Serpens is a constellation of the northern hemisphere. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy, it remains one of the 88 modern constellations defined by the International Astronomical Union, it is unique among the modern constellations in being split into two non-contiguous parts, Serpens Caput to the west and Serpens Cauda to the east. Between these two halves lies the constellation of Ophiuchus, the "Serpent-Bearer". In figurative representations, the body of the serpent is represented as passing behind Ophiuchus between Mu Serpentis in Serpens Caput and Nu Serpentis in Serpens Cauda; the brightest star in Serpens is the red giant star Alpha Serpentis, or Unukalhai, in Serpens Caput, with an apparent magnitude of 2.63. Located in Serpens Caput are the naked-eye globular cluster Messier 5 and the naked-eye variables R Serpentis and Tau4 Serpentis. Notable extragalactic objects include one of the densest galaxy clusters known. Part of the Milky Way's galactic plane passes through Serpens Cauda, therefore rich in galactic deep-sky objects, such as the Eagle Nebula and its associated star cluster Messier 16.
The nebula measures 70 light-years by 50 light-years and contains the Pillars of Creation, three dust clouds that became famous for the image taken by the Hubble Space Telescope. Other striking objects include the Red Square Nebula, one of the few objects in astronomy to take on a square shape. In Greek mythology, Serpens represents a snake held by the healer Asclepius. Represented in the sky by the constellation Ophiuchus, Asclepius once killed a snake, but the animal was subsequently resurrected after a second snake placed a revival herb on it before its death; as snakes shed their skin every year, they were known as the symbol of rebirth in ancient Greek society, legend says Asclepius would revive dead humans using the same technique he witnessed. Although this is the logic for Serpens' presence with Ophiuchus, the true reason is still not known. Sometimes, Serpens was depicted as coiling around Ophiuchus, but the majority of atlases showed Serpens passing either behind Ophiuchus' body or between his legs.
In some ancient atlases, the constellations Serpens and Ophiuchus were depicted as two separate constellations, although more they were shown as a single constellation. One notable figure to depict Serpens separately was Johann Bayer; when Eugène Delporte established modern constellation boundaries in the 1920s, he elected to depict the two separately. However, this posed the problem of how to disentangle the two constellations, with Deporte deciding to split Serpens into two areas—the head and the tail—separated by the continuous Ophiuchus; these two areas became known as Serpens Caput and Serpens Cauda, caput being the Latin word for head and cauda the Latin word for tail. In Chinese astronomy, most of the stars of Serpens represented part of a wall surrounding a marketplace, known as Tianshi, in Ophiuchus and part of Hercules. Serpens contains a few Chinese constellations. Two stars in the tail represented part of the tower with the market office. Another star in the tail represented jewel shops.
One star in the head marked the crown prince's wet nurse, or sometimes rain. There were two "serpent" constellations in Babylonian astronomy, known as Bašmu, it appears that Mušḫuššu was depicted as a hybrid of a dragon, a lion and a bird, loosely corresponded to Hydra. Bašmu was a horned serpent and corresponds to the Ὄφις constellation of Eudoxus of Cnidus on which the Ὄφις of Ptolemy is based. Serpens is the only one of the 88 modern constellations to be split into two disconnected regions in the sky: Serpens Caput and Serpens Cauda; the constellation is unusual in that it depends on another constellation for context. Serpens Caput is bordered by Libra to the south, Virgo and Boötes to the east, Corona Borealis to the north, Ophiuchus and Hercules to the west. Covering 636.9 square degrees total, it ranks 23rd of the 88 constellations in size. It appears prominently in both the northern and southern skies during the Northern Hemisphere's summer, its main asterism consists of 11 stars, 108 stars in total are brighter than magnitude 6.5, the traditional limit for naked-eye visibility.
Serpens Caput's boundaries, as set by Eugène Delporte in 1930, are defined by a 15-sided polygon, while Serpens Cauda's are defined by a 25-sided polygon. In the equatorial coordinate system, the right ascension coordinates of Serpens Caput's borders lie between 15h 10.4m and 16h 22.5m, while the declination coordinates are between 25.66° and −03.72°. Serpens Cauda's boundaries lie between right ascensions of 17h 16.9m and 18h 58.3m and declinations of 06.42° and −16.14°. The International Astronomical Union adopted the three-letter abbreviation "Ser" for the constellation in 1922. Marking the heart of the serpent is the constellation's brightest star, Alpha Serpentis. Traditionally called Unukalhai, is a red giant of spectral type K2III located 23 parsecs distant with a visual magnitude of 2.630 ± 0.009, meaning it can be seen with the naked eye in
Corona Australis is a constellation in the Southern Celestial Hemisphere. Its Latin name means "southern crown", it is the southern counterpart of Corona Borealis, the northern crown, it is one of the 48 constellations listed by the 2nd-century astronomer Ptolemy, it remains one of the 88 modern constellations. The Ancient Greeks saw Corona Australis as a wreath rather than a crown and associated it with Sagittarius or Centaurus. Other cultures have likened the pattern to a turtle, ostrich nest, a tent, or a hut belonging to a rock hyrax. Although fainter than its northern counterpart, the oval- or horseshoe-shaped pattern of its brighter stars renders it distinctive. Alpha and Beta Coronae Australis are the two brightest stars with an apparent magnitude of around 4.1. Epsilon Coronae Australis is the brightest example of a W Ursae Majoris variable in the southern sky. Lying alongside the Milky Way, Corona Australis contains one of the closest star-forming regions to the Solar System—a dusty dark nebula known as the Corona Australis Molecular Cloud, lying about 430 light years away.
Within it are stars at the earliest stages of their lifespan. The variable stars R and TY Coronae Australis light up parts of the nebula, which varies in brightness accordingly; the name of the constellation was entered as "Corona Australis" when the International Astronomical Union established the 88 modern constellations in 1922. In 1932, the name was instead recorded as "Corona Austrina" when the IAU's commission on notation approved a list of four-letter abbreviations for the constellations; the four-letter abbreviations were repealed in 1955. The IAU presently uses "Corona Australis" exclusively. Corona Australis is a small constellation bordered by Sagittarius to the north, Scorpius to the west, Telescopium to the south, Ara to the southwest; the three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is'CrA'. The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of four segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 17h 58.3m and 19h 19.0m, while the declination coordinates are between −36.77° and −45.52°.
Covering 128 square degrees, Corona Australis culminates at midnight around the 30th of June and ranks 80th in area. Only visible at latitudes south of 53° north, Corona Australis cannot be seen from the British Isles as it lies too far south, but it can be seen from southern Europe and from the southern United States. While not a bright constellation, Corona Australis is nonetheless distinctive due to its identifiable pattern of stars, described as horseshoe- or oval-shaped. Though it has no stars brighter than 4th magnitude, it still has 21 stars visible to the unaided eye. Nicolas Louis de Lacaille used the Greek letters Alpha through to Lambda to label the most prominent eleven stars in the constellation, designating two stars as Eta and omitting Iota altogether. Mu Coronae Australis, a yellow star of spectral type G5.5III and apparent magnitude 5.21, was labelled by Johann Elert Bode and retained by Benjamin Gould, who deemed it bright enough to warrant naming. The only star in the constellation to have received a name is Alfecca Meridiana or Alpha CrA.
The name combines the Arabic name of the constellation with the Latin for "southern". In Arabic, Alfecca means "break", refers to the shape of both Corona Australis and Corona Borealis. Called "Meridiana", it is a white main sequence star located 125 light years away from Earth, with an apparent magnitude of 4.10 and spectral type A2Va. A rotating star, it spins at 200 km per second at its equator, making a complete revolution in around 14 hours. Like the star Vega, it has excess infrared radiation, which indicates it may be ringed by a disk of dust, it is a main-sequence star, but will evolve into a white dwarf. Beta Coronae Australis is an orange giant 474 light years from Earth, its spectral type is K0II, it is of apparent magnitude 4.11. Since its formation, it has evolved from a B-type star to a K-type star, its luminosity class places it as a bright giant. 100 million years old, it has a radius of 43 solar radii and a mass of between 4.5 and 5 solar masses. Alpha and Beta are so similar; some of the more prominent double stars include Gamma Coronae Australis—a pair of yellowish white stars 58 light years away from Earth, which orbit each other every 122 years.
Widening since 1990, the two stars can be seen as separate with a 100 mm aperture telescope. They have a combined visual magnitude of 4.2. Epsilon Coronae Australis is an eclipsing binary belonging to a class of stars known as W Ursae Majoris variables; these star systems are known as contact binaries as the component stars are so close together they touch. Varying by a quarter of a magnitude around an average apparent magnitude of 4.83 every seven hours, the star system lies 98 light years away. Its spectral type is F4VFe-0.8+. At the southern end of the crown asterism are the stars Eta¹ and Eta² Coronae Australis, which form an optical double. Of magnitude 5.1 and 5.5, they are both white. Kappa Coronae Australis is an resolved optical double—the components are of apparent magnitudes 6.3 and 5.6 and are
Telescopium is a minor constellation in the southern celestial hemisphere, one of twelve named in the 18th century by French astronomer Nicolas-Louis de Lacaille and one of several depicting scientific instruments. Its name is a Latinized form of the Greek word for telescope. Telescopium was much reduced in size by Francis Baily and Benjamin Gould; the brightest star in the constellation is Alpha Telescopii, a blue-white subgiant with an apparent magnitude of 3.5, followed by the orange giant star Zeta Telescopii at magnitude 4.1. Eta and PZ Telescopii are two young star systems with brown dwarf companions. Telescopium hosts two unusual stars with little hydrogen that are to be the result of two merged white dwarfs: PV Telescopii known as HD 168476, is a hot blue extreme helium star, while RS Telescopii is an R Coronae Borealis variable. RR Telescopii is a cataclysmic variable that brightened as a nova to magnitude 6 in 1948. Telescopium was introduced in 1751–52 by Nicolas-Louis de Lacaille with the French name le Telescope, depicting an aerial telescope, after he had observed and catalogued 10,000 southern stars during a two-year stay at the Cape of Good Hope.
He devised 14 new constellations in uncharted regions of the Southern Celestial Hemisphere not visible from Europe. All but one honored instruments that symbolised the Age of Enlightenment. Covering 40 degrees of the night sky, the telescope stretched out northwards between Sagittarius and Scorpius. Lacaille had Latinised its name to Telescopium by 1763; the constellation was known by other names. It was called Tubus Astronomicus in the eighteenth century, during which time three constellations depicting telescopes were recognised—Tubus Herschelii Major between Gemini and Auriga and Tubus Herschelii Minor between Taurus and Orion, both of which had fallen out of use by the nineteenth century. Johann Bode called it the Astronomische Fernrohr in his 1805 Gestirne and kept its size, but astronomers Francis Baily and Benjamin Gould subsequently shrank its boundaries; the much-reduced constellation lost several brighter stars to neighbouring constellations: Beta Telescopii became Eta Sagittarii, which it had been before Lacaille placed it in Telescopium, Gamma was placed in Scorpius and renamed G Scorpii by Gould, Theta Telescopii reverted to its old appellation of d Ophiuchi, Sigma Telescopii was placed in Corona Australis.
Uncatalogued, the latter is now known as HR 6875. The original object Lacaille had named Eta Telescopii—the open cluster Messier 7—was in what is now Scorpius, Gould used the Bayer designation for a magnitude 5 star, which he felt warranted a letter. A small constellation, Telescopium is bordered by Sagittarius and Corona Australis to the north, Ara to the west, Pavo to the south, Indus to the east, cornering on Microscopium to the northeast; the three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is'Tel'. The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a quadrilateral. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 18h 09.1m and 20h 29.5m, while the declination coordinates are between −45.09° and −56.98°. The whole constellation is visible to observers south of latitude 33°N. Within the constellation's borders, there are 57 stars brighter than or equal to apparent magnitude 6.5.
With a magnitude of 3.5, Alpha Telescopii is the brightest star in the constellation. It is a blue-white subgiant of spectral type B3IV, it is radiating nearly 800 times the Sun's luminosity, is estimated to be 5.2±0.4 times as massive and have 3.3±0.5 times the Sun's radius. Close by Alpha Telescopii are the two blue-white stars sharing the designation of Delta Telescopii. Delta¹ Telescopii is of spectral type B6IV and apparent magnitude 4.9, while Delta² Telescopii is of spectral type B3III and magnitude 5.1. They form an optical double, as the stars are estimated to be around 710 and 1190 light-years away respectively; the faint Gliese 754, a red dwarf of spectral type M4.5V, is one of the nearest 100 stars to Earth at 19.3 light-years distant. Its eccentric orbit around the Galaxy indicates that it may have originated in the Milky Way's thick disk. At least four of the fifteen stars visible to the unaided eye are orange giants of spectral class K; the second brightest star in the constellation—at apparent magnitude 4.1—is Zeta Telescopii, an orange subgiant of spectral type K1III-IV.
Around 1.53 times as massive as the Sun, it shines with 512 times its luminosity. Located 127 light years away from Earth, it has been described as reddish in appearance. Epsilon Telescopii is a binary star system: the brighter component, Epsilon Telescopii A, is an orange giant of spectral type K0III with an apparent magnitude of +4.52, while the 13th magnitude companion, Epsilon Telescopii B, is 21 arcseconds away from the primary, just visible with a 15 cm aperture telescope on a dark night. The system is 417 light-years away. Iota Telescopii and HD 169405—magnitude 5 orange giants of spectral types K0III and K0.5III respectively—make up the quartet. They are around 497 light-years away from the Sun respectively. Another ageing star, Kappa Telescopii is a yellow giant with a spectral type G9III and apparent magnitude of 5.18. Around 1.87 billion years old, this star of around 1.6 solar masses has swollen to 11 times the Sun's diameter. It is 293 light-years from Earth, is another optical double.
Xi Telescopii is an irregular variable star that ranges between magnitudes 4.89 and 4.94. Located 1079 light-years distant, it is a red giant of spectral type M2III that has a diameter around 5.6 times the Sun's, a luminosity around 2973 times
The Milky Way is the galaxy that contains our Solar System. The name describes the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye; the term Milky Way is a translation of the Latin via lactea, from the Greek γαλαξίας κύκλος. From Earth, the Milky Way appears as a band. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610; until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies; the Milky Way is a barred spiral galaxy with a diameter between 200,000 light-years. It is estimated to contain 100 -- more than 100 billion planets; the Solar System is located at a radius of 26,490 light-years from the Galactic Center, on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust.
The stars in the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge. The galactic center is an intense radio source known as Sagittarius A*, assumed to be a supermassive black hole of 4.100 million solar masses. Stars and gases at a wide range of distances from the Galactic Center orbit at 220 kilometers per second; the constant rotation speed contradicts the laws of Keplerian dynamics and suggests that much of the mass of the Milky Way is invisible to telescopes, neither emitting nor absorbing electromagnetic radiation. This conjectural mass has been termed "dark matter"; the rotational period is about 240 million years at the radius of the Sun. The Milky Way as a whole is moving at a velocity of 600 km per second with respect to extragalactic frames of reference; the oldest stars in the Milky Way are nearly as old as the Universe itself and thus formed shortly after the Dark Ages of the Big Bang. The Milky Way has several satellite galaxies and is part of the Local Group of galaxies, which form part of the Virgo Supercluster, itself a component of the Laniakea Supercluster.
The Milky Way is visible from Earth as a hazy band of white light, some 30° wide, arching across the night sky. In night sky observing, although all the individual naked-eye stars in the entire sky are part of the Milky Way, the term “Milky Way” is limited to this band of light; the light originates from the accumulation of unresolved stars and other material located in the direction of the galactic plane. Dark regions within the band, such as the Great Rift and the Coalsack, are areas where interstellar dust blocks light from distant stars; the area of sky that the Milky Way obscures is called the Zone of Avoidance. The Milky Way has a low surface brightness, its visibility can be reduced by background light, such as light pollution or moonlight. The sky needs to be darker than about 20.2 magnitude per square arcsecond in order for the Milky Way to be visible. It should be visible if the limiting magnitude is +5.1 or better and shows a great deal of detail at +6.1. This makes the Milky Way difficult to see from brightly lit urban or suburban areas, but prominent when viewed from rural areas when the Moon is below the horizon.
Maps of artificial night sky brightness show that more than one-third of Earth's population cannot see the Milky Way from their homes due to light pollution. As viewed from Earth, the visible region of the Milky Way's galactic plane occupies an area of the sky that includes 30 constellations; the Galactic Center lies in the direction of Sagittarius. From Sagittarius, the hazy band of white light appears to pass around to the galactic anticenter in Auriga; the band continues the rest of the way around the sky, back to Sagittarius, dividing the sky into two equal hemispheres. The galactic plane is inclined by about 60° to the ecliptic. Relative to the celestial equator, it passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux, indicating the high inclination of Earth's equatorial plane and the plane of the ecliptic, relative to the galactic plane; the north galactic pole is situated at right ascension 12h 49m, declination +27.4° near β Comae Berenices, the south galactic pole is near α Sculptoris.
Because of this high inclination, depending on the time of night and year, the arch of the Milky Way may appear low or high in the sky. For observers from latitudes 65° north to 65° south, the Milky Way passes directly overhead twice a day; the Milky Way is the second-largest galaxy in the Local Group, with its stellar disk 100,000 ly in diameter and, on average 1,000 ly thick. The Milky Way is 1.5 trillion times the mass of the Sun. To compare the relative physical scale of the Milky Way, if the Solar System out to Neptune were the size of a US quarter, the Milky Way would be the size of the contiguous United States. There is a ring-like filament of stars rippling above and below the flat galactic plane, wrapping around the Milky Way at a diameter of 150,000–180,000 light-years, which may be part of the Milky Way itself. Estimates of the mass of the Milky Way vary, depending upon the method and data used; the low end of the estimate range is 5.8×1011 solar masses, somewhat less than that of the Andromeda Galaxy.
Measurements using the Very Long Baseline Array in 2009 found
Scutum is a small constellation introduced in the seventeenth century. Its name is Latin for shield. Scutum was named in 1684 by Polish astronomer Johannes Hevelius, who named it Scutum Sobiescianum to commemorate the victory of the Christian forces led by Polish King John III Sobieski in the Battle of Vienna in 1683; the name was shortened to Scutum. Five bright stars of Scutum were known as 1, 6, 2, 3, 9 Aquilae respectively. Coincidentally, the Chinese associated these stars with battle armor, incorporating them into the larger asterism known as Tien Pien, i.e. the Heavenly Casque. Scutum is not a bright constellation, with the brightest star, Alpha Scuti, at magnitude 3.85. But some stars are notable in the constellation. Beta Scuti is the second brightest at magnitude 4.22, followed by Delta Scuti at magnitude 4.72. Beta Scuti is a binary system, with the primary with a spectral type similar to the Sun, although it is 1,270 times brighter. Delta Scuti is a bluish white giant star, now coming at the direction of the Solar System.
Within 1.3 million years it will come as close to 10 light years from Earth, will be much brighter than Sirius by that time. UY Scuti is a red supergiant pulsating variable star and is one of the largest stars known with a radius over 1,000 times that of the Sun. Although not a large constellation, Scutum contains several open clusters, as well as a globular cluster and a planetary nebula; the two best known deep sky objects in Scutum are M11 and the open cluster M26. The globular cluster NGC 6712 and the planetary nebula IC 1295 can be found in the eastern part of the constellation, only 24 arcminutes apart; the most prominent open cluster in Scutum is the Wild Duck Cluster, M11. It was named by William Henry Smyth in 1844 for its resemblance in the eyepiece to a flock of ducks in flight; the cluster, 6200 light-years from Earth and 20 light-years in diameter, contains 3000 stars, making it a rich cluster. It is 220 million years old; the space probe. It will not be nearing the closest star in this constellation for over a million years at present speed, by which time its batteries will be long dead.
Taurus Poniatovii - a constellation created by the Polish astronomer Marcin Odlanicki Poczobutt in 1777 to honor King of Poland Stanisław August Poniatowski. Ian Ridpath and Wil Tirion. Stars and Planets Guide, London. ISBN 978-0-00-823927-5. Princeton University Press, Princeton. ISBN 978-0-69-117788-5; the Deep Photographic Guide to the Constellations: Scutum Star Tales – Scutum