Perseus is a constellation in the northern sky, being named after the Greek mythological hero Perseus. It is bordered by Aries and Taurus to the south, Auriga to the east, Camelopardalis and Cassiopeia to the north, and Andromeda and Triangulum to the west. Covering 615 square degrees, it ranks twenty-fourth of the 88 constellations in size. It appears prominently in the northern sky during the Northern Hemisphere’s spring. Its main asterism consists of 19 stars. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 01h 29.1m and 04h 51.2m, while the declination coordinates are between 30.92° and 59.11°.
Perseus holding the decapitated head of Medusa the Gorgon, as depicted on Chart IV in the Uranographia of Johann Bode (1801). On the forehead of the Gorgon lies the star Algol, famous for its variations in light.
[http://www.ianridpath.com/startales/perseus.htm]
The constellation of Perseus may be derived from the Babylonian Old Man (MUL.SHU.GI) constellation, then associated with East in the MUL.APIN- an astronomical compilation dating to around 1000 BCE.
In Greek mythology, Perseus was the son of Danae, who was sent by King Polydectes to bring the head of Medusa the Gorgon- whose visage caused all who gazed upon her to turn to stone. Perseus slew Medusa in her sleep, and Pegasus and Chrysaor appeared from her body. Perseus continued to the realm of Cepheus whose daughter Andromeda was to be sacrificed to Cetus the sea monster. Perseus rescued Andromeda from the monster by killing it with his diamond sword. He turned Polydectes and his followers to stone with Medusa’s head and appointed Dictys the fisherman king. Perseus and Andromeda married and had six children.
Four Chinese constellations are contained in the area of the sky identified with Perseus in the West. Tiānchuán, the Celestial Boat, was the third paranatellon (a star or constellation which rises at the same time as another star or object) of the third house of the White Tiger of the West, representing the boats that Chinese people were reminded to build in case of a catastrophic flood season. Incorporating stars from the northern part of the constellation, it contained Mu, Delta, Psi, Alpha, Gamma and Eta Persei. Jīshuǐ, the Swollen Waters, was the fourth paranatellon of the aforementioned house, representing the potential of unusually high floods during the end of August and beginning of September at the beginning of the flood season. Lambda and possibly Mu Persei lay within it. Dàlíng, the Great Trench, was the fifth paranatellon of that house, representing the trenches where criminals executed en masse in August were interred. It was formed by Kappa, Omega, Rho, 24, 17 and 15 Persei. The pile of corpses prior to their interment was represented by Jīshī (Algol), the sixth paranatellon of the house. The Double Cluster, h and Chi Persei, had special significance in Chinese astronomy. Known as Hsi and Ho, the two clusters represented two astronomers who failed to predict a total solar eclipse and were subsequently beheaded.
In Polynesia, Perseus was not commonly recognized as a separate constellation; the only people that named it were those of the Society Islands, who called it Faa-iti, meaning ‘Little Valley.’ Algol may have been named Matohi by the Māori people, but the evidence for this identification is disputed. Matohi (‘Split’) occasionally came into conflict with Tangaroa-whakapau over which of them should appear in the sky, the outcome affecting the tides. It matches the Maori description of a blue-white star near Aldebaran but does not disappear as the myth would indicate.
[http://astropixels.com/constellations/charts/Per.html]
[https://theberkshireedge.com/eyes-to-the-sky-perseus-the-hero-in-the-milky-way/]
The galactic plane of the Milky Way passes through Perseus, whose brightest star is the yellow-white supergiant Alpha Persei (also called Mirfak or Mirphak), which shines at magnitude 1.79. It and many of the surrounding stars are members of an open cluster known as the Alpha Persei Cluster. The best-known star, however, is Algol (Beta Persei), linked with ominous legends because of its variability, which is noticeable to the naked eye:
The Alpha Persei Cluster, also known as Melotte 20 or Collinder 39, is an open cluster in the constellation of Perseus. To the naked eye, the cluster consists of several blue spectral type B type stars. The most luminous member is the ~2nd magnitude white-yellow supergiant Mirfak, also known as Alpha Persei. Bright members also include Delta, Sigma, Psi, 29, 30, 34 and 48 Persei.
[https://en.wikipedia.org/wiki/Alpha_Persei_Cluster]
Alpha Persei, also named Mirfak, is the brightest star in the northern constellation of Perseus, just outshining the constellation’s best known star, Algol. It lies in the midst of a cluster of stars named as the eponymous Alpha Persei Cluster, or Melotte 20, which is easily visible in binoculars and includes many of the fainter stars in the constellation. It has an apparent visual magnitude of 1.8, and is a circumpolar star when viewed from mid-northern latitudes. Determined distance using the trigonometric parallax, places the star 510 light-years (160 parsecs) from the Sun.
The spectrum of Alpha Persei matches a stellar classification of F5 Ib, revealing it to be a supergiant star in the latter stages of its evolution. Mirfak has about 8.5 times the Sun’s mass and has expanded to roughly 60 times the size of the Sun. It is radiating 5,000 times as much luminosity as the Sun from its outer atmosphere at an effective temperature of 6,350 K, which creates the yellow-white glow of an F-type star.
The name Mirfak is Arabic in origin, meaning ‘Elbow.’
[https://en.wikipedia.org/wiki/Alpha_Persei]
The Algol system on 12 August 2009. This is a CHARA interferometer image with ½-milliarcsecond resolution in the near-infrared H-band. The elongated appearance of Algol Aa2 (labelled B) and the round appearance of Algol Aa1 (labelled A) are real, but the form of Algol Ab (labelled C) is an artifact.
Algol, designated Beta Persei, is a bright multiple star in the constellation of Perseus. It is the first and best known eclipsing binary, and one of the first non-nova variable stars to be discovered. It is a three-star system, consisting of Beta Persei Aa1, Aa2, and Ab- in which the large and bright primary β Persei Aa1 is regularly eclipsed by the dimmer β Persei Aa2. Thus, Algol’s magnitude is usually near-constant at 2.1, but regularly dips to 3.4 every 2.86 days during the roughly 10-hour-long partial eclipses. There is also a secondary eclipse (the ‘second minimum’) when the brighter star occults the fainter secondary. Algol gives its name to its class of eclipsing variable, known as Algol variables.
Algol is about 92.8 light-years from the Sun, but about 7.3 million years ago it passed within 9.8 light-years of the Solar System and its apparent magnitude was about -2.5, which is considerably brighter than the star Sirius is today. Because the total mass of the Algol system is about 5.8 solar masses, at the closest approach this might have given enough gravity to perturb the Oort cloud of the Solar System somewhat and hence increase the number of comets entering the inner Solar System. However, the actual increase in net cometary collisions is thought to have been quite small.
The name Algol derives from Arabic ra’s al-ghūl: head (ra’s) of the ogre (al-ghūl). The English name ‘Demon Star’ is a direct translation of this.
[https://en.wikipedia.org/wiki/Algol]
Zeta Persei (Atik) is a star in the northern constellation of Perseus. With an apparent visual magnitude of 2.9, it can be readily seen with the naked eye. Parallax measurements place it at a distance of about 750 light-years (230 parsecs) from Earth.
This is a lower luminosity supergiant star with a stellar classification of B1 Ib. It is an enormous star, with an estimated 26-27 times the Sun’s radius and 13-16 times the Sun’s mass. It has about 47,000 times the luminosity of the Sun and it is radiating this energy at an effective temperature of 20,800 K, giving it the blue-white hue of a B-type star.
Zeta Persei has a 9th magnitude companion at an angular separation of 12.9 arcseconds. The two stars have the same proper motion, so they may be physically associated. If so, they are separated by at least 4,000 Astronomical Units.
It is a confirmed member of the Perseus OB2 association (Per OB2), also called the Zeta Persei association, which is a moving group of stars that includes 17 massive, high luminosity members with spectral types of O or B, giving them a blue hue. These stars have a similar trajectory through space, suggesting they originated in the same molecular cloud and are about the same age.
[https://en.wikipedia.org/wiki/Zeta_Persei]
Epsilon Persei is a multiple star system in the northern constellation of Perseus. It has a combined apparent visual magnitude of +2.88, which is bright enough to be viewed with the naked eye. Based upon parallax measurements, this system is located at a distance of roughly 640 light-years (196 parsecs) from Earth.
This is a spectroscopic binary system, which means that the presence of an orbiting companion has been revealed by radial velocity variations in the spectrum of the primary. The two components are orbiting each other with a period of 14 days at a high orbital eccentricity of 0.55. The secondary component has about 6-13% of the primary’s mass and may have a stellar classification in the range from A6 V to K1 V. There may be a third component to this system with an orbital period of roughly 9,428 days (25.8 years), although this has not been conclusively demonstrated.
The primary component of this system, Epsilon Persei A, is a massive star with 12-16 times the Sun’s mass and near eight times the radius of the Sun. It has a stellar classification of B0.5 V, making it a B-type main sequence star that is generating energy at its core through the nuclear fusion of hydrogen. Component A is radiating over 28,000 times the Sun’s luminosity from its outer envelope at an effective temperature of 26,500 K. This gives the star the blue-white hue that is typical of B-type stars.
Epsilon Persei A is a Beta Cephei variable star with a primary pulsation period of 0.1603 days, or 6.24 cycles per day. It may have multiple pulsation frequencies.
[https://en.wikipedia.org/wiki/Epsilon_Persei]
Gamma Persei is a binary star system in the constellation Perseus. The combined apparent visual magnitude of the pair is +2.9, making it the fourth-brightest member of the constellation. The distance to this system has been measured using the parallax technique, giving an estimate of roughly 243 light-years (75 parsecs). About 4° to the north of Gamma Persei is the radiance point for the annual Perseid meteor shower.
This is a wide eclipsing binary system with an orbital period of 5,329.8 days (14.6 years). This eclipse was first observed in 1990 and lasted for two weeks. During an eclipse, the primary passes in front of the secondary, causing the magnitude of the system to decrease by 0.55. The primary component of this system is a giant star with a stellar classification of G9 III. It has a projected rotational velocity of 50.0 km s−1 and a lengthy estimated rotation period of 14.6 years. The classification of the secondary remains tentative, with assignments of A3V and A2(III).
[https://en.wikipedia.org/wiki/Gamma_Persei]
Xi Persei, traditionally known as Menkhib, a blue giant of spectral type O7III, is one of the hottest bright stars in the sky, with a surface temperature of 37,500 K. It is one of the more massive stars, being between 26 and 32 solar masses, and is 330,000 times as luminous as our Sun:
Xi Persei can be seen together with the California Nebula, white and reddish from low-left to up-right. The bow shock in front of the runaway star is the green patch. Xi Per itself can be seen as a faint blue spot on the lower edge of the bow shock.
Menkib (Xi Persei) is one of the very few naked-eye O stars and one of the hottest and most massive stars visible without the aid of a telescope. The fact that it is only the twelfth brightest star in the constellation Perseus is due to its great distance and also because about half of its light is absorbed by dust in the plane of the Milky Way. Menkib is probably responsible for illuminating the California Nebula (NGC 1499). Its name, meaning ‘collarbone,’ refers to a larger Arabic constellation of which Atik is the ‘shoulder.’ It is slightly unstable, changing its brightness by about 5%, and also blowing a powerful stellar wind by which it sheds about a millionth of a solar mass per year. Though the star’s status is uncertain- somewhere between giant and supergiant- it has almost certainly stopped core hydrogen fusion, and may even be fusing helium, already having lost some 10% of its original mass. Still only a few million years old, it will explode sometime in the next million years or so. Like Naos, it is also one of the sky’s few runaway stars. For reasons still uncertain, it is traveling at high speed away from its birthplace in the Perseus OB2 Association (which also contains it sister star Atik), the acceleration caused either by a close encounter with another star or by the explosion of a now-dead and even more massive companion. Menkib has a present companion, a much smaller star, about which nothing is known, in a 7-day orbit.
[http://www.daviddarling.info/encyclopedia/M/Menkib.html]
GK Persei, also known as Nova Persei 1901, is a bright nova that appeared halfway between Algol and Delta Persei. Discovered on 21 February 1901 by Scottish amateur astronomer Thomas David Anderson, it peaked at magnitude 0.2- almost as bright as Capella and Vega. It faded to magnitude 13 around 30 years after its peak brightness:
GK Per: Nova of 1901
Early in the 20th century, GK Persei briefly became one of the brightest stars in planet Earth's sky, an event known as Nova Persei 1901. Documented in this modern day composite of two images from 2003 and 2011 the ejecta from the explosion, popularly called the Firework Nebula, continues to expand into space. These images are part of a time lapse video tracking the nebula's expansion over the last 17 years. About 1500 light-years away, the nebula is still just under a light-year in diameter. GK Per and similar cataclysmic variable stars known as classical novae are understood to be binary systems consisting of a compact white dwarf star and swollen cool giant star in a close orbit. The build- up of mass transferred to the surface of the white dwarf from the giant star through an accretion disk eventually triggers a thermonuclear outburst, blasting the stellar material into space without destroying the white dwarf star. With a 2 day orbital period, the GK Per system has produced much smaller outbursts in recent years.
[https://apod.nasa.gov/apod/ap111105.html]
Seven stars in Perseus have been found to have planetary systems. V718 Persei is a star in the young open cluster IC 348 that appears to be periodically eclipsed by a giant planet every 4.7 years. This has been inferred to be an object with a maximum mass of 6 times that of Jupiter and an orbital radius of 3.3 AU.
The galactic plane of the Milky Way passes through Perseus, but is much less obvious than elsewhere in the sky as it is mostly obscured by molecular clouds. The Perseus Arm is a spiral arm of the Milky Way galaxy and stretches across the sky from the constellation Cassiopeia through Perseus and Auriga to Gemini and Monoceros. This segment is towards the rim of the galaxy.
The Double Cluster (NGC 869 and NGC 884)
Within the Perseus Arm lie two open clusters (NGC 869 and NGC 884) known as the Double Cluster. Sometimes known as h and Chi (χ) Persei respectively, they are easily visible through binoculars and small telescopes. Both lie more than 7,000 light-years from Earth and are several hundred light-years apart. The Double Cluster was first recorded during the reign of the Chinese king Tsung-K'ang, who reigned during the Xia dynasty (2858- 2146 BCE). Both clusters are of approximately magnitude 4 and 0.5 degrees in diameter. The clusters are both distinct from the surrounding star field and are clearly concentrated at their centers. The constituent stars, numbering over 100 in each cluster, range widely in brightness.
There are many nebulae in Perseus. These include the planetary nebula M76 (Little Dumbbell Nebula), the emission nebula NGC 1499 (California Nebula), and the reflection nebula NGC 1333:
Messier 76
“Nebula at the right foot of Andromeda ...” begins the description for the 76th object in Charles Messier’s 18th century Catalog of Nebulae and Star Clusters. In fact, M76 is one of the fainter objects on the Messier list and is also known by the popular name of the ‘Little Dumbbell Nebula.’ Like its brighter namesake M27 (the Dumbbell Nebula), M76 is recognized as a planetary nebula- a gaseous shroud cast off by a dying sunlike star. The nebula itself is thought to be shaped more like a donut, while the box-like appearance of its brighter central region is due to our nearly edge-on view. Gas expanding more rapidly away from the donut hole produces the fainter loops of far flung material. The fainter material is emphasized in this composite image, highlighted by showing emission from hydrogen atoms in orange and oxygen atoms in complementary blue hues. The nebula's dying star can be picked out in the sharp false-color image as the blue-tinted star near the center of the box-like shape. Distance estimates place M76 about 3 to 5 thousand light-years away, making the nebula over a light-year in diameter.
[http://apod.nasa.gov/apod/ap100723.html]
The California Nebula
What’s California doing in space? Drifting through the Orion Arm of the spiral Milky Way Galaxy, this cosmic cloud by chance echoes the outline of California on the west coast of the United States. Our own Sun also lies within the Milky Way’s Orion Arm, only about 1,500 light-years from the California Nebula. Also known as NGC 1499, the classic emission nebula is around 100 light-years long. On the featured image, the most prominent glow of the California Nebula is the red light characteristic of hydrogen atoms recombining with long lost electrons, stripped away (ionized) by energetic starlight. The star most likely providing the energetic starlight that ionizes much of the nebular gas is the bright, hot, bluish Xi Persei just to the right of the nebula. A regular target for astrophotographers, the California Nebula can be spotted with a wide-field telescope under a dark sky toward the constellation of Perseus, not far from the Pleiades.
[http://apod.nasa.gov/apod/ap160112.html]
NGC 1333 Stardust
NGC 1333 is seen in visible light as a reflection nebula, dominated by bluish hues characteristic of starlight reflected by dust. A mere 1,000 light-years distant toward the heroic constellation Perseus, it lies at the edge of a large, star-forming molecular cloud. This striking close-up view spans about two full moons on the sky or just over 15 light-years at the estimated distance of NGC 1333. It shows details of the dusty region along with hints of contrasting red emission from Herbig-Haro objects, jets and shocked glowing gas emanating from recently formed stars. In fact, NGC 1333 contains hundreds of stars less than a million years old, most still hidden from optical telescopes by the pervasive stardust. The chaotic environment may be similar to one in which our own Sun formed over 4.5 billion years ago.
[http://apod.nasa.gov/apod/ap140306.html]
Perseus contains some notable galaxies. NGC 1260 is either a lenticular or tightly-wound spiral galaxy about 76.7 million pc (250 million ly) from Earth. It was the host galaxy of the supernova SN 2006gy, one of the brightest ever recorded:
SN 2006gy: NASA’s Chandra Sees Brightest Supernova Ever
According to observations by NASA’s Chandra X-ray Observatory and ground-based optical telescopes, the supernova SN 2006gy is the brightest and most energetic stellar explosion ever recorded and may be a long-sought new type of explosion. The top panel of this graphic is an artist’s illustration that shows what SN 2006gy may have looked like if viewed at a close distance. The fireworks-like material in white shows the explosion of an extremely massive star. This debris is pushing back two lobes of cool, red gas that were expelled in a large eruption from the star before it exploded. The green, blue and yellow regions in these lobes shows where gas is being heated in a shock front as the explosion material crashes into it and pushes it backwards. Most of the optical light generated by the supernova is thought to come from debris that has been heated by radioactivity, but some likely comes from the shocked gas.
The bottom left panel is an infrared image, using adaptive optics at the Lick Observatory, of NGC 1260, the galaxy containing SN 2006gy. The dimmer source to the lower left in that panel is the center of NGC 1260, while the much brighter source to the upper right is SN 2006gy. The panel to the right shows Chandra’s X-ray image of the same field of view, again showing the nucleus of NGC 1260 and SN 2006gy. The Chandra observation allowed astronomers to determine that SN 2006gy was indeed caused by the collapse of an extremely massive star, and not the most likely alternative explanation for the explosion, the destruction of a low-mass star. If the supernova was caused by a white dwarf star exploding into a dense, hydrogen-rich environment, SN 2006gy would have been about 1,000 times brighter in X-rays than what Chandra detected.
[http://chandra.harvard.edu/photo/2007/sn2006gy/index.html]
NGC 1275 is a Seyfert galaxy containing an active nucleus that produces jets of material, surrounding the galaxy with massive bubbles. This galaxy has undergone many galactic mergers throughout its existence, as evidenced by the ‘high velocity system’ -the remnants of a smaller galaxy- surrounding it. Its active nucleus is a strong source of radio waves:
Hubble Remix: Active Galaxy NGC 1275
Active galaxy NGC 1275 is the central, dominant member of the large and relatively nearby Perseus Cluster of Galaxies. Wild-looking at visible wavelengths, the active galaxy is also a prodigious source of x-rays and radio emission. NGC 1275 accretes matter as entire galaxies fall into it, ultimately feeding a supermassive black hole at the galaxy’s core. This color composite image, recreated from archival Hubble Space Telescope data, highlights the resulting galactic debris and filaments of glowing gas, some up to 20,000 light-years long. The filaments persist in NGC 1275, even though the turmoil of galactic collisions should destroy them. What keeps the filaments together? Observations indicate that the structures, pushed out from the galaxy’s center by the black hole’s activity, are held together by magnetic fields. Also known as Perseus A, NGC 1275 spans over 100,000 light years and lies about 230 million light years away.
[http://apod.nasa.gov/apod/ap131006.html]
NGC 1275 is the brightest member of the Perseus cluster (Abell 426), a massive galaxy cluster located 76.6 million pc (250 million ly) from Earth. With a redshift of 0.0179, Abell 426 is the closest major cluster to the Earth:
Galaxies of the Perseus Cluster
This colorful telescopic skyscape is filled with galaxies that lie nearly 250 million light-years away, the galaxies of the Perseus cluster. Their extended and sometimes surprising shapes are seen beyond a veil of foreground stars in our own Milky Way. Ultimately consisting of over a thousand galaxies, the cluster is filled with yellowish elliptical and lenticular galaxies, like those scattered throughout this view of the cluster’s central region. Notably, the large galaxy at the left is the massive and bizarre-looking NGC 1275. A prodigious source of high-energy emission, active galaxy NGC 1275 dominates the Perseus cluster, accreting matter as entire galaxies fall into it and feed the supermassive black hole at the galaxy’s core. Of course, spiral galaxies also inhabit the Perseus cluster, including the small, face-on spiral NGC 1268, right of picture center. The bluish spot on the outskirts of NGC 1268 is supernova SN 2008fg. At the estimated distance of the Perseus galaxy cluster, this field spans about 1.5 million light-years.
[http://apod.nasa.gov/apod/ap090508.html]
Perseus is also home to the Perseid annual meteor shower. The Perseids appear to radiate from Perseus from mid-July, peaking in activity between 9 and 14 August each year. Associated with Comet Swift- Tuttle, they have been observed for about 2,000 years:
Perseid Meteors over China
Comet dust rained down on planet Earth earlier this month, streaking through dark skies in the annual Perseid meteor shower. While enjoying the anticipated space weather above Zhangbei Prairie, Hebei Province, China, astronomer Xiang Zhan recorded a series of 10 second long exposures spanning four hours on the night of August 12/13 (2013) using a wide angle lens. Combining frames which captured 68 meteor flashes, he produced the above composite view of the Perseids of summer. Although the sand-sized comet particles are traveling parallel to each other, the resulting shower meteors clearly seem to radiate from a single point on the sky in the eponymous constellation Perseus. The radiant effect is due to perspective, as the parallel tracks appear to converge at a distance. The next notable meteor shower may be the Orionids in late October.
[http://apod.nasa.gov/apod/ap130821.html]
[https://en.wikipedia.org/wiki/Perseus_%28constellation%29]
No comments:
Post a Comment