Pisces constellation lies in the northern sky. Its name means ‘fish’ in Latin. It is the 14th constellation in size, occupying an area of 889 square degrees. It is located in the first quadrant of the northern hemisphere (NQ1) and can be seen at latitudes between +90° and -65°. The neighboring constellations are Andromeda, Aquarius, Aries, Cetus, Pegasus and Triangulum.
[http://www.constellation-guide.com/constellation-list/pisces-constellation/]
The ecliptic and the celestial equator intersect within this constellation and in Virgo. The vernal equinox is currently located in Pisces, due south of ω Psc, and, due to precession, slowly drifting below the western fish towards Aquarius.
Pisces spans the 330° to 360° of the zodiac, between 332.75° and 360° of celestial longitude. Under the tropical zodiac the sun transits this area on average between February 19 and March 20, and under the sidereal zodiac, the sun transits this area between approximately March 13 and April 13. While the astrological sign Pisces per definition runs from ecliptical longitude 330° to 0, this position is now mostly covered by the constellation of Aquarius, due to the precession from when the constellation and the sign coincided. According to some tropical astrologers, the current astrological age is the Age of Pisces, while others maintain that it is the Age of Aquarius. The symbol of the fish is derived from the ichthyocentaurs, who aided Aphrodite when she was born from the sea.
[https://en.wikipedia.org/wiki/Pisces_(astrology)]
A cord joins the tails of Pisces, the two fish. From the Atlas Coelestis of John Flamsteed (1729)
[http://www.ianridpath.com/startales/pisces.htm]
Pisces originates from some composition of the Babylonian constellations Šinunutu ‘the great swallow’ in current western Pisces, and Anunitum the ‘Lady of the Heaven,’ at the place of the northern fish. In the first-millennium BCE texts known as the Astronomical Diaries, part of the constellation was also called DU.NU.NU (Rikis-nu.mi, ‘the fish cord or ribbon’).
In Greek mythology, Pisces is associated with Aphrodite and Eros, who escaped from the monster Typhon by leaping into the sea and transforming themselves into fish. In order not to lose each other, they tied themselves together with rope. The Romans adopted the Greek legend, with Venus and Cupid acting as the counterparts for Aphrodite and Eros. The knot of the rope is marked by Alpha Piscium (α Psc), also called Al-Rischa (‘the cord’ in Arabic).
Johannes Hevelius regarded the constellation Pisces as being composed of four subdivisions. In 1754, the astronomer John Hill proposed to treat part of Pisces as a separate constellation, called Testudo (the Turtle), in which the star 20 Psc was intended to be the head of the turtle. However the proposal was largely neglected by other astronomers with the exception of Admiral Smyth.
The Fishes are also associated with the German legend of Antenteh, who owned just a tub and a crude cabin when he met a magical fish. They offered him a wish, which he refused. However, his wife begged him to return to the fish and ask for a beautiful furnished home. This wish was granted, but her desires were not satisfied. She then asked to be a queen and have a palace, but when she asked to become a goddess, the fish became angry and took the palace and home, leaving the couple with the tub and cabin once again. The tub in the story is sometimes recognized as the Great Square of Pegasus.
The stars of Pisces were incorporated into several constellations in Chinese astronomy. Wai-ping (‘Outer Enclosure’) was a fence that kept a pig farmer from falling into the marshes and kept the pigs where they belonged. It was represented by Alpha, Delta, Epsilon, Zeta, Mu, Nu, and Xi Piscium. The marshes were represented by the four stars designated Phi Ceti. The northern fish of Pisces was a part of the House of the Sandal, Koui-siou.
[http://www.dibonsmith.com/psc_con.htm]
Constellation of Pisces
[https://www.davidmalin.com/fujii/source/Psc.html]
Stars of Pisces include:
Eta Piscium (Kullat Nunu) is the brightest star in the constellation. It has an apparent visual magnitude of 3.62 and is approximately 294 light years distant from the solar system. The star belongs to the spectral class G7 IIIa, which means that it is a yellow giant. It has a faint companion about an arcsecond away. Eta Piscium is 316 times more luminous than the Sun and a mass 3.5 to 4 times solar. It is 26 times larger than the Sun. The star has an unofficial proper name, Kullat Nunu. Nunu is the Babylonian word for ‘fish,’ and ‘kullat’ refers either to a bucket or the cord used to tie the fish together.
Gamma Piscium is a yellow giant with the stellar classification of G9 III. It is the second brightest star in Pisces. It has an apparent visual magnitude of 3.699 and is approximately 138 light years distant. The star is ten times the size of the Sun and 61 times more luminous. It is believed to be about 5.5 billion years old. The star is part of an asterism called the Circlet of Pisces, which represents the head of the western fish in Pisces constellation. Gamma Piscium will not be in the Sun’s vicinity for long. The star moves three quarters of an arcsecond across the sky every year.
Omega Piscium is a yellow-white subgiant star with the stellar classification of F4IV. It has an apparent magnitude of 4.036 and is approximately 106 light years distant from the Sun. It is the first star to the east of the Circlet of Pisces. The star is suspected to be a close binary system. If it is a single star, it is 1.8 times more massive than the Sun and 20 times more luminous.
Iota Piscium is a yellow-white dwarf with the stellar classification of F7 V. It has an apparent visual magnitude of 4.13 and is 44.73 light years distant from Earth. It is larger and more luminous than the Sun. Iota Piscium is a suspected variable star, and it has two line-of-sight companions.
Omicron Piscium is a yellow giant star with the stellar classification G8 III. It has an apparent magnitude of 4.26 and is approximately 142 light years distant. In the 1515 Almagest, the star was listed with the proper name Torcularis septentrionalis.
Alpha Piscium (Alrescha) is a close binary star with components separated by 1.8 arcseconds. The primary star belongs to the spectral class A0p and has a visual magnitude of 4.33, and the companion belongs to the spectral class A3m and has an apparent magnitude of 5.23. The stars orbit each other with a period of over 700 years. The primary star has 2.3 solar masses and is 31 times more luminous than the Sun, while the companion has 1.8 times the Sun’s mass and is 12 times brighter. The name Alrescha (sometimes Al Rescha, Alrisha, or Alrischa) is derived from the Arabic al-rišā, which means ‘the well rope.’ The star is also sometimes known as Kaitain and Okda. Okda is derived from uqdah, the Arabic word for ‘knot.’ Alpha Piscium has a combined apparent magnitude of 3.82 and is approximately 139 light years distant from the solar system.
Beta Piscium (Fum al Samakah) is a blue-white main sequence star with the stellar classification B6Ve. It has a visual magnitude of 4.53 and is approximately 492 light years distant from the Sun. The star’s traditional name, Fum al Samakah, comes from the Arabic phrase fum al-samakah, which means ‘the mouth of the fish.’
The Circlet asterism is located south of Pegasus constellation, in the western fish of Pisces. It is formed by the stars Gamma, Kappa, Lambda, TX, Iota and Theta Piscium.
[http://www.constellation-guide.com/constellation-list/pisces-constellation/]
Deep-sky objects in Pisces include:
The grand-design spiral galaxy Messier 74 as photographed by the Hubble Space Telescope in 2007. ESO’s PESSTO survey has captured this view of Messier 74, a stunning spiral galaxy with well-defined whirling arms. However, the real subject of this image is the galaxy’s brilliant new addition from late July 2013: a Type II supernova named SN2013ej that is visible as the brightest star at the bottom left of the image.
Messier 74 (M74), nicknamed the Phantom Galaxy, is a grand design spiral galaxy located in the constellation Pisces.
The galaxy appears face-on and has an apparent magnitude of 10. It lies at an approximate distance of 30 million light years from Earth. Its designation in the New General Catalogue is NGC 628. Messier 74 occupies an area of 10.5 by 9.5 arc minutes of apparent sky, which corresponds to a linear diameter of 95,000 light years, almost the size of the Milky Way. The galaxy is home to about 100 billion stars. It can be found 1.5 degrees east-northeast of Kullat Nunu (Eta Piscium), the brightest star in Pisces.
Messier 74 is a perfect example of a grand design spiral galaxy. It has two clearly defined spiral arms and its face-on orientation and large apparent size make it a frequent target for astronomers looking to study spiral arm structure. The spiral arms, which extend for about 1,000 light years, contain clusters of young blue stars and many starforming nebulae. The galaxy is receding from us at 793 km/s.
The symmetric appearance of M74 is suspected to be the result of density waves sweeping around the galaxy’s gaseous disk which, in turn, is the result of M74’s gravitational interaction with neighboring galaxies. The interaction and collisions of the galaxies’ clouds are also responsible for the star forming activity seen along the spiral arms of M74.
Three supernovae have been detected in M74 in recent decades: SN 2002ap in 2002, SN 2003gd in 2003, and SN 2013ej in 2013.
SN 2002ap was one of the extremely rare Type Ic supernovae, also known as hypernovae, recently seen within 10 megaparsecs of the solar system. The hypernova reached a peak magnitude of 12.3.
SN 2003gd was classified as a Type II-P supernova, one with a known luminosity, which helps astronomers to measure distances. The supernova occurred 9.6 megaparsecs or 31 million light years from Earth and reached a magnitude of 13.2. It was one of the few supernova events that had a ‘light echo,’ a reflection of the explosion that appeared after the supernova event itself. The progenitor star was a red, M-class supergiant.
SN2013ej was first detected on July 25, 2013 about 2.7 arc minutes from the galaxy’s core and reached a peak magnitude of 12.5. It was classified as a Type II supernova, which means that it resulted from a massive star collapsing inward onto its unstable core and exploding. The progenitor star was likely a red supergiant.
In March 2005, the Chandra X-ray Observatory detected an ultraluminous X-ray source (ULX) in the galaxy. The object has an estimated mass about 10,000 times that of the Sun and radiates more X-ray power than a neutron star in intervals of about two hours. The discovery indicates that there is an intermediate-mass black hole in the center of M74. The X-ray source is identified as CXOU J013651.1+154547. A total of 21 X-ray sources have been discovered within the inner 5 arc minutes from the galaxy’s core.
Messier 74 is the central galaxy in the M74 Group, a small group consisting of 5 to 7 galaxies. The M74 Group includes the peculiar Sm galaxy UGC 891, several irregular galaxies- UGC 1176, UGC 1195, UGCA 20- and the peculiar and unique polar-ring spiral galaxy NGC 660.
[http://www.messier-objects.com/messier-74-phantom-galaxy/]
NGC 488
NGC 488 is a face-on spiral galaxy in the constellation Pisces. It is at a distance of about 90 million light-years away from Earth. Its diametre is estimated to be 52,6 Kpc (171.000 ly). The galaxy has a large central bulge and is considered the prototype galaxy with multiple spiral arms. Its arms are tightly wound. Star forming activity has been traced within the arms. The nucleus of NGC 488 has been found to be chemically decoupled, being twice metal rich as the central bulge of the galaxy. NGC 488, with the exception of its smaller companions, that form NGC 488 group, is an isolated galaxy.
[https://en.wikipedia.org/wiki/NGC_488]
Polar Ring Galaxy NGC 660
NGC 660 is featured in this cosmic snapshot, a sharp composite of broad and narrow band filter image data from the Gemini North telescope on Mauna Kea. Over 20 million light-years away and swimming within the boundaries of the constellation Pisces, NGC 660’s peculiar appearance marks it as a polar ring galaxy. A rare galaxy type, polar ring galaxies have a substantial population of stars, gas, and dust orbiting in rings nearly perpendicular to the plane of the galactic disk. The bizarre-looking configuration could have been caused by the chance capture of material from a passing galaxy by a disk galaxy, with the captured debris eventually strung out in a rotating ring. The violent gravitational interaction would account for the myriad pinkish star forming regions scattered along NGC 660’s ring. The polar ring component can also be used to explore the shape of the galaxy’s otherwise unseen dark matter halo by calculating the dark matter’s gravitational influence on the rotation of the ring and disk. Broader than the disk, NGC 660’s ring spans over 50,000 light-years.
[http://apod.nasa.gov/apod/ap141108.html]
NGC 520
NGC 520 is the product of a collision between two disc galaxies that started 300 million years ago. It exemplifies the middle stages of the merging process: the discs of the parent galaxies have merged together, but the nuclei have not yet coalesced. It features an odd-looking tail of stars and a prominent dust lane that runs diagonally across the center of the image and obscures the galaxy. NGC 520 is one of the brightest galaxy pairs on the sky, and can be observed with a small telescope toward the constellation of Pisces, the Fish, having the appearance of a comet. It is about 100 million light-years away and about 100,000 light-years across. The galaxy pair is included in Arp’s catalogue of peculiar galaxies as ARP 157.
[https://www.spacetelescope.org/images/heic0810aq/]
Arp 227 is a system of interacting galaxies:
Shell Galaxies in Pisces
This colorful cosmic skyscape features a peculiar system of galaxies cataloged as Arp 227 some 100 million light-years distant. Swimming within the boundaries of the constellation Pisces, Arp 227 consists of the two galaxies prominent on the left; the curious shell galaxy NGC 474 and its blue, spiral-armed neighbor NGC 470. The faint, wide arcs or shells of NGC 474 could have been formed by a gravitational encounter with neighbor NGC 470. Alternately the shells could be caused by a merger with a smaller galaxy producing an effect analogous to ripples across the surface of a pond. Remarkably, the large galaxy on the right hand side of the deep image, NGC 467, appears to be surrounded by faint shells too, evidence of another interacting galaxy system. Intriguing background galaxies are scattered around the field that also includes spiky foreground stars. Of course, those stars lie well within our own Milky Way Galaxy. The field of view spans 25 arc minutes or about 1/2 degree on the sky.
[https://apod.nasa.gov/apod/ap110226.html]
CL 0024+1654 is a massive galaxy cluster that lenses the galaxy behind it, creating arc-shaped images of the background galaxy. The cluster is primarily made up of yellow elliptical and spiral galaxies, at a distance of 3.6 billion light-years from Earth (redshift 0.4), half as far away as the background galaxy, which is at a distance of 5.7 billion light-years (redshift 1.67):
Giant Cluster Bends, Breaks Images
What are those strange blue objects? Many of the brightest blue images are of a single, unusual, beaded, blue, ring-like galaxy which just happens to line-up behind a giant cluster of galaxies. Cluster galaxies here typically appear yellow and- together with the cluster’s dark matter- act as a gravitational lens. A gravitational lens can create several images of background galaxies, analogous to the many points of light one would see while looking through a wine glass at a distant street light. The distinctive shape of this background galaxy- which is probably just forming- has allowed astronomers to deduce that it has separate images at 4, 10, 11, and 12 o’clock, from the center of the cluster. A blue smudge near the cluster center is likely another image of the same background galaxy. In all, a recent analysis postulated that at least 33 images of 11 separate background galaxies are discernable. This spectacular photo of galaxy cluster CL0024+1654 from the Hubble Space Telescope was taken in November 2004.
[http://apod.nasa.gov/apod/ap090823.html]
BP Psc is a Sun- like star which has expanded into the red giant phase likely consuming a star or planet in the process:
BP Psc: Chandra Finds Evidence for Stellar Cannibalism
BP Psc is a star like our Sun, but one that is more evolved, about 1,000 light years away. New evidence from Chandra supports the case that BP Psc is not a very young star as previously thought. Rather, BP has spent its nuclear fuel and expanded into its "red giant" phase – likely consuming a star or planet in the process. Studying this type of stellar ‘cannibalism’ may help astronomers better understand how stars and planets interact as they age.
The composite image on the left shows X-ray and optical data for BP Piscium (BP Psc), a more evolved version of our Sun about 1,000 light years from Earth. Chandra X-ray Observatory data are colored in purple, and optical data from the 3-meter Shane telescope at Lick Observatory are shown in orange, green and blue. BP Psc is surrounded by a dusty and gaseous disk and has a pair of jets several light years long blasting out of the system. A close-up view is shown by the artist’s impression on the right. For clarity a narrow jet is shown, but the actual jet is probably much wider, extending across the inner regions of the disk. Because of the dusty disk, the star’s surface is obscured in optical and near-infrared light. Therefore, the Chandra observation is the first detection of this star in any wavelength.
The disk and the jets, seen distinctly in the optical data, provide evidence for a recent and catastrophic interaction in which BP Psc consumed a nearby star or giant planet. This happened when BP Psc ran out of nuclear fuel and expanded into its ‘red giant’ phase.
Jets and a disk are often characteristics of very young stars, so astronomers thought BP Psc might be one as well. However, the new Chandra results argue against this interpretation, because the X-ray source is fainter than expected for a young star. Another argument previously used against the possible youth of BP Psc was that it is not located near any star-forming cloud and there are no other known young stars in its immediate vicinity. The Chandra image supports this absence of a cluster of young stars, since multiwavelength studies show that most of the X-ray sources in the composite image are likely to be rapidly growing supermassive black holes in the centers of distant galaxies.
[http://chandra.harvard.edu/photo/2010/bppsc/index.html]
[https://en.wikipedia.org/wiki/Pisces_(constellation)]
No comments:
Post a Comment