Mira

Mira as seen by Hubble. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into NASA image. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program
Observation data Epoch J2000.0
Constellation (pronunciation)	Cetus
Right ascension	02h 19m 20. In Astronomy, an epoch is a moment in time used as a reference for the Orbital elements of a Celestial body. In Astronomy, an epoch is a moment in time used as a reference for the Orbital elements of a Celestial body. In common usage a constellation is a group of celestial bodies that are connected together in some arrangement typically stars to form a visible figure or picture Each culture has its own Constellations usually based on Mythology. Cetus ( Κῆτος Kētos, referring to the sea monster Cetus) is a Constellation of the northern winter sky in the region known as the Water Right ascension (abbrev RA; symbol α) is the Astronomical term for one of the two Coordinates of a point on the Celestial sphere 7927s[1]
Declination	-02° 58′ 39. In Astronomy, declination (abbrev dec or δ) is one of the two coordinates of the Equatorial coordinate system, the other being either 513″[1]
Apparent magnitude (V)	2. The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 0 to 10. 1
Characteristics
Spectral type	M7 IIIe[2]
U-B color index	+0. In Astronomy, stellar classification is a classification of Stars based initially on photospheric temperature and its associated Spectral characteristics In Astronomy, the color index is a simple numerical expression that determines the color of an object which in the case of a Star gives its Temperature 08[3]
B-V color index	+1. In Astronomy, the color index is a simple numerical expression that determines the color of an object which in the case of a Star gives its Temperature 53[3]
Variable type	Mira variable
Astrometry
Radial velocity (Rv)	+63. For the astronomical object see Variable star. Variable Star is a 2006 novel written by Spider Robinson Mira variables, named after the star Mira (ˈmairə are a class of pulsating Variable stars characterized by very red colors pulsation periods longer than 100 days Astrometry is the branch of Astronomy that relates to precise measurements and explanations of the positions and movements of Stars and other celestial bodies Radial velocity is the Velocity of an object in the direction of the line of sight (i 8[1] km/s
Proper motion (μ)	RA: 10. The proper motion of a Star is the measurement of its change in position in the sky over time after Improper motions are accounted for 33[1] mas/yr Dec. A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60 of one degree. A year (from Old English gēr) is the time between two recurrences of an event related to the Orbit of the Earth around the Sun : -239. 48[1] mas/yr
Parallax (π)	7. A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60 of one degree. A year (from Old English gēr) is the time between two recurrences of an event related to the Orbit of the Earth around the Sun Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between 79 ± 1. 07[1] mas
Distance	approx. A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60 of one degree. Distance is a numerical description of how far apart objects are 420 ly (approx. A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by 130 pc)
Absolute magnitude (MV)	0. History The first direct measurements of an object at interstellar distances were undertaken by German Astronomer Friedrich Wilhelm Bessel in 1838 In Astronomy, absolute magnitude (also known as absolute visual magnitude) is the Apparent magnitude an object would have if it were at a standard 93
Details
Mass	1. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object 18[4] M☉
Radius	332–402[5] R☉
Luminosity	8400–9360[5] L☉
Temperature	2918–3192[5] K
Age	6×109[4] years
Other designations
Stella Mira, Collum Ceti, Wonderful Star,[6] Omicron Ceti, 68 Ceti, HR 681, BD −03°353, HD 14386, LTT 1179, SAO 129825, HIP 10826. The solar mass is a standard way to express Mass in Astronomy, used to describe the masses of other Stars and galaxies. Remote Authentication Dial In User Service ( RADIUS) is a networking protocol that provides centralized access authorization and accounting management for people or computers In Astronomy, the solar radius is a unit of Length used to express the size of Stars It is equal to the current radius of the Sun. Luminosity has different meanings in several different fields of science The solar luminosity, L_\odot is a unit of Luminosity ( power emitted in the form of Photons conventionally used by Astronomers to Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth A year (from Old English gēr) is the time between two recurrences of an event related to the Orbit of the Earth around the Sun A star catalogue, or star catalog, is an Astronomical catalogue that lists Stars In Astronomy, many stars are referred to simply by catalogue The Bright Star Catalogue, also known as the Yale Catalogue of Bright Stars or Yale Bright Star Catalogue, is a Star catalogue that lists of all stars of In Astronomy, Durchmusterung or Bonner Durchmusterung ( BD) is the usual name for three comprehensive astrometric Star catalogues The Henry Draper Catalogue ( HD) is an Astronomical Star catalogue published between 1918 and 1924 giving Spectroscopic classifications A star catalogue, or star catalog, is an Astronomical catalogue that lists Stars In Astronomy, many stars are referred to simply by catalogue The Smithsonian Astrophysical Observatory (SAO is a "research institute" of the Smithsonian Institution headquartered in Cambridge Massachusetts, The Hipparcos and Tycho Catalogues (Tycho-1 are the primary products of the European Space Agency 's astrometric mission Hipparcos. [1]

Mira, pronounced /ˈmaɪrə/, also known as Omicron Ceti (or ο Ceti / ο Cet), is a red giant star estimated 200-400 light years away in the constellation Cetus. Omicron or Omikron (uppercase Ο, lowercase ο, literally "small o": Όμικρον o mikron, micron meaning 'small' in contrast A red giant is a luminous Giant star of low or intermediate mass (roughly 0 A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by In common usage a constellation is a group of celestial bodies that are connected together in some arrangement typically stars to form a visible figure or picture Cetus ( Κῆτος Kētos, referring to the sea monster Cetus) is a Constellation of the northern winter sky in the region known as the Water Mira is a binary star, consisting of the red giant Mira A along with Mira B. A binary star is a Star system consisting of two Stars orbiting around their Center of mass. A red giant is a luminous Giant star of low or intermediate mass (roughly 0 Mira B, also known as VZ Ceti, is the companion star to the Variable star Mira. Mira A is also an oscillating variable star and was the first non-supernova variable star discovered, with the possible exception of Algol. For the astronomical object see Variable star. Variable Star is a 2006 novel written by Spider Robinson A supernova (plural supernovae or supernovas) is a stellar Explosion. Algol (β Per / Beta Persei known colloquially as the Demon Star, is a bright Star in the Constellation Perseus. Apart from the unusual Eta Carinae, Mira is the brightest periodic variable in the sky that is not visible to the naked eye for part of its cycle. Eta Carinae (η Carinae or η Car is a Hypergiant Luminous blue variable Star in the Carina constellation. Its distance is uncertain; pre-Hipparcos estimates centered around 220 light-years,(1) while Hipparcos data suggests a distance of 418 light-years, albeit with a margin of error of ~14%. Hipparcos (an Acronym for Hi gh P recision Par allax Co llecting S atellite) was an Astrometry mission A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by The margin of error is a statistic expressing the amount of random Sampling error in a survey 's results

Observation history

Evidence that the variability of Mira was known in ancient China, Babylon or Greece is at best only circumstantial. Chinese civilization originated in various city-states along the Yellow River ( valley in the Neolithic era Babylon was a City-state of ancient Mesopotamia, the remains of which can be found in present-day Al Hillah, Babil Province, Iraq The term ancient Greece refers to the period of Greek history lasting from the Greek Dark Ages ca ^[7] What is certain is that the variability of Mira was recorded by the astronomer David Fabricius beginning on August 3, 1596. David Fabricius ( March 9, 1564, Esens - May 7, 1617, Osteel) was a German theologian who made two major Events 8 - Roman Empire General Tiberius defeats Dalmatians on the river Bathinus. Observing the planet Mercury, he needed a reference star for comparing positions and picked a previously unremarked third-magnitude star nearby. By August 21, however, it had increased in brightness by one magnitude, then by October had faded from view. Events 1192 - Minamoto Yoritomo becomes Seii Tai Shōgun and the De facto ruler of Japan. The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value Fabricius assumed it was a nova, but then saw it again on February 16, 1609 ^[8]. Events 1249 - Andrew of Longjumeau is dispatched by Louis IX of France as his ambassador to meet with the Khan of the Mongols

Eventually, Johann Holwarda determined a period of the star's reappearances, eleven months; Johannes Hevelius was observing it at the same time and named it "Mira" (meaning "wonderful, astonishing") in 1662's Historiola Mirae Stellae, for it acted like no other known star. Johannes Phocylides Holwarda ( Jan Fokkesz Jan Fokker Johann Holwarda Johannes Fokkes Holwarda Jan Fokkens Holwarda Jan Fokkes van Holwerd) (1618— January 22, Johannes Hevelius ( Latin) also called Johannes Hewel Johann Hewelke Johannes Höwelcke in German, or Jan Heweliusz (in Polish) Ismail Bouillaud then estimated its period at 333 days, less than one day off the modern value of 332 days (and perfectly forgivable, as Mira is known to vary slightly in period, and may even be slowly changing over time). Ismaël Bullialdus ( September 28, 1605 - November 25, 1694 (age 89 was a French Astronomer.

There is considerable speculation as to whether Mira had been observed prior to Fabricius. Certainly Algol's history (known for certain as a variable only in 1667, but with legends and such dating back to antiquity showing that it had been observed with suspicion for millennia) suggests that Mira might have been known too. Algol (β Per / Beta Persei known colloquially as the Demon Star, is a bright Star in the Constellation Perseus. Karl Manitius, a translator of Hipparchus' Commentary on Aratus, has suggested that certain lines from that second century text may be about Mira. Hipparchus ( Greek; ca 190 BC &ndash ca 120 BC was a Greek Astronomer, Geographer, and Mathematician of the Hellenistic The other pre-telescopic Western catalogs of Ptolemy, al-Sufi, Ulugh Beg, and Tycho Brahe turn up no mentions, even as a regular star. Claudius Ptolemaeus ( Greek: Klaúdios Ptolemaîos; after 83 &ndash ca Ulugh Beg ( Chaghatay / - also Uluğ Bey, Ulugh Bek and Ulug Bek) (c Tycho Brahe, born Tyge Ottesen Brahe ( December 14 1546 &ndash October 24 1601) was a Danish nobleman There are three observations from Chinese and Korean archives, in 1596, 1070, and the same year when Hipparchus would have made his observation (134 BC) that are suggestive, but the Chinese practice of pinning down observations no more precisely than within a given Chinese constellation makes it difficult to be sure.

System

Component A

Mira A generated energy by nuclear fusion of hydrogen to form helium at its core. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Once the supply of hydrogen at the core was exhausted, fusion of hydrogen continued along a shell surrounding the inert helium core. This shell generated more energy from fusion than did the core, so the luminosity of Mira A increases. However, at the same time, the outer atmosphere of Mira A expanded to many times its original size, producing a red giant. A red giant is a luminous Giant star of low or intermediate mass (roughly 0 ^[9]

As additional helium was generated by the hydrogen-burning shell, the dormant helium core of Mira A steadily increased in mass. Once the core reached a temperature and pressure sufficient to begin burning helium, Mira A underwent a runaway process called the helium flash. A helium flash is the sudden beginning of Helium fusion in the core of intermediate mass Stars of less than about 2 This initiates the fusion of helium in the core, producing an ash of carbon and oxygen. Gradually the core expanded and cooled, and decreased energy was generated from hydrogen-burning. This caused the luminosity of the star to decrease, while the outer atmosphere shrank and increased in temperature. This stage of a star's evolution is called the horizontal branch. The horizontal branch ( HB) is a stage of Stellar evolution which immediately follows the Red giant branch in stars whose masses are similar to the Sun's ^[9]

When the supply of helium at the core became exhausted, a new helium-burning shell forms around the inactive core of carbon and oxygen. Once more Mira A began to expand, increasing in luminosity while the surface temperature decreased. This stage is known as the Asymptotic Giant Branch (AGB),^[9] and Mira A is currently at this phase of its evolution. The asymptotic giant branch is the region of the Hertzsprung-Russell diagram populated by evolving low to medium-mass Stars This is a period of Stellar evolution ^[10]

Mira as seen from the Earth

Once the temperature above Mira's helium burning shell rose to about 10⁷K, hydrogen became ignited along a shell at that radius. However, because energy is now less readily transported through the hydrogen burning region, pressure builds up between the layers. This causes the hydrogen burning layer to rise until the fusion is shut off by lower temperatures. Mira then contracts and the hydrogen layer re-ignites. The result is an instability in Mira known as the thermally pulsing AGB phase. Each pulse lasts a decade or more, and on the order of 10,000 years passes between each pulse. With every pulse cycle Mira increases in luminosity and the pulses grow stronger. This is also causing dynamic instability in Mira, resulting in dramatic changes in luminosity and size over shorter, irregular time periods. ^[11]

The overall shape of Mira A has been observed to change, exhibiting pronounced departures from symmetry. These appear to be caused by bright spots on the surface that evolve their shape on time scales of 3–14 months. Observations of Mira A in the ultraviolet band by the Hubble Space Telescope have shown a plume-like feature pointing toward the companion star. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into ^[10]

Variability

Mira A is a well-known example of a category of variable stars known as Mira variables, which are named after this star. For the astronomical object see Variable star. Variable Star is a 2006 novel written by Spider Robinson Mira variables, named after the star Mira (ˈmairə are a class of pulsating Variable stars characterized by very red colors pulsation periods longer than 100 days It—and the other 6000 or so known stars of this class—are all red giants whose surfaces oscillate in such a way as to increase and decrease in brightness over periods ranging from about 80 days to more than 1000. A red giant is a luminous Giant star of low or intermediate mass (roughly 0

In the particular case of Mira, its increases in brightness take it up to about magnitude 3. The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 5 on average, placing it among the brighter stars in the Cetus constellation. This is the list of notable Stars in the Constellation Cetus, sorted by decreasing brightness Individual cycles vary too; well-attested maxima go as high as magnitude 2. 0 in brightness and as low as 4. 9, a range almost 15 times in brightness, and there are historical suggestions that the real spread may be three times this or more. Minima range much less, and have historically been between 8. 6 and 10. 1, a factor of four times in luminosity. The total swing in brightness from absolute maximum to absolute minimum (two events which did not occur on the same cycle) is 1700 times. Interestingly, since Mira emits the vast majority of its radiation in the infrared, its variability in that band is only about two magnitudes. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of (2) The shape of its light curve is of an increase over about 100 days, and a return twice as long. In Astronomy, a light curve is a graph of light intensity of a Celestial object or region as a function of time . ^[12]

Mass loss

Ultra-violet studies of Mira by NASA's Galaxy Evolution Explorer (Galex) space telescope have revealed that it sheds a trail of material from the outer envelope, creating a tail 13 light-years in length, formed over tens of thousands of years ^[13][14]. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program The Galaxy Evolution Explorer is an Orbiting Ultraviolet Space telescope that was launched on April 28, 2003. It is thought that a hot bow-wave of compressed plasma/gas is the cause of the tail; the bow-wave is a result of the interaction of the stellar wind from Mira A with gas in the interstellar space, through which Mira is moving at an extremely high speed of 130 kilometres/second ^[15][16]. A bow shock is a boundary between a Magnetosphere and an ambient medium The tail consists of material stripped from the head of the bow-wave, which is also visible in ultra-violet observations.

Component B

Main article: Mira B

The companion star was resolved by the Hubble Space Telescope in 1995, when it was 70 astronomical units from the primary; results were announced in 1997. Mira B, also known as VZ Ceti, is the companion star to the Variable star Mira. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the The HST ultraviolet images and later X-ray images by the Chandra space telescope show a spiral of gas rising off Mira in the direction of Mira B. The Chandra X-ray Observatory is a Satellite launched on STS-93 by NASA on July 23, 1999. The companion's orbital period around Mira is approximately 400 years. The orbital period is the time taken for a given object to make one complete Orbit about another object

In 2007, observations showed a protoplanetary disc around the companion, Mira B. A protoplanetary disk (or proplyd) is a rotating Circumstellar disk of dense gas surrounding a young newly formed star a T Tauri star or Herbig star This disc is being accreted from material in the solar wind from Mira and may eventually go on to form new planets. A stellar wind is a flow of neutral or charged gas ejected from the upper atmosphere of a Star. These observations also revealed that the companion is most likely a main sequence star of around 0. The main sequence is the name for a continuous and distinctive band of stars that appear on a plot of stellar color versus brightness 7 solar masses and spectral type K, instead of a white dwarf as previously believed ^[17]. The solar mass is a standard way to express Mass in Astronomy, used to describe the masses of other Stars and galaxies. In Astronomy, stellar classification is a classification of Stars based initially on photospheric temperature and its associated Spectral characteristics A white dwarf, also called a degenerate dwarf, is a small Star composed mostly of Electron-degenerate matter.

References

See also

• Mira in fiction

External links

• Mira – Bizarre Star at NASA
• History of Mira's Discovery at AAVSO
• Mira has tail nearly 13 light years in length (BBC)
• Speeding Bullet Star Leaves Enormous Streak Across Sky at Caltech
• Astronomy Picture of the Day:
  1998-10-11, 2001-01-21, 2006-07-22, 2007-02-21, 2007-08-17
• Mira (Omicron Ceti). The Planetary systems of Stars other than the Sun and its Solar System are a staple element in much Science fiction. Since its founding in 1911 the American Association of Variable Star Observers (AAVSO has coordinated collected evaluated analyzed published and archived Variable star The California Institute of Technology (commonly referred to as Caltech) is a private, Coeducational research university located in Pasadena The Astronomy Picture of the Day ( APOD) Website is a service provided by NASA and Michigan Technological University (MTU The Encyclopedia of Astrobiology, Astronomy, and Spaceflight. Retrieved on June 22, 2006. Events 217 BC - Battle of Raphia: Ptolemy IV of Egypt defeats Antiochus III the Great of the Seleucid kingdom. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar.
• Mira. Alcyone Ephemeris. Retrieved on 2006-08-25. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1248 - The Dutch city of Ommen receives city rights and fortification rights from Otto III the
• Interferometric observations of the Mira star o Ceti with the VLTI/VINCI instrument in the near-infrared.
• Robert Burnham Jr. , Burnham's Celestial Handbook, Vol. 1, (New York: Dover Publications, Inc. , 1978), 634.
• James Kaler, The Hundred Greatest Stars, (New York: Copernicus Books, 2002), 121.
• SEDS article
• A recent lightcurve of Mira from the BAV.