Mira (), designation Omicron Ceti (ο Ceti, abbreviated Omicron Cet, ο Cet), is a red-giant

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

estimated to be 200–300

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s from the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Cetus Cetus () is a constellation, sometimes called 'the whale' in English. The Cetus (mythology), Cetus was a sea monster in Greek mythology which both Perseus and Heracles needed to slay. Cetus is in the region of the sky that contains other water- ...

. ο Ceti is a binary stellar system, consisting of a variable red giant (Mira A) along with a

white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...

companion ( Mira B). Mira A is a pulsating

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

and was the first non-

supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...

discovered, with the possible exception of

Algol ALGOL (; short for "Algorithmic Language") is a family of imperative computer programming languages originally developed in 1958. ALGOL heavily influenced many other languages and was the standard method for algorithm description used by the ...

. It is the prototype of the

Mira variable Mira variables (named for the prototype star Mira) are a class of pulsating stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than one magnitude in infrared and 2.5 magnitude at visual wave ...

Nomenclature

ο Ceti ( Latinised to ''Omicron Ceti'') is the star's

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...

. It was named Mira (

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

for 'wonderful' or 'astonishing') by

Johannes Hevelius Johannes Hevelius Some sources refer to Hevelius as Polish: * * * * * * * Some sources refer to Hevelius as German: * * * * *of the Royal Society * (in German also known as ''Hevel''; ; – 28 January 1687) was a councillor and mayor of Danz ...

in his ''Historiola Mirae Stellae'' (1662). In 2016, the

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...

(WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN, which included Mira for this star. MiraCC

Observation history

Evidence that the variability of Mira was known in

ancient China The history of China spans several millennia across a wide geographical area. Each region now considered part of the Chinese world has experienced periods of unity, fracture, prosperity, and strife. Chinese civilization first emerged in the Y ...

Babylon Babylon ( ) was an ancient city located on the lower Euphrates river in southern Mesopotamia, within modern-day Hillah, Iraq, about south of modern-day Baghdad. Babylon functioned as the main cultural and political centre of the Akkadian-s ...

Greece Greece, officially the Hellenic Republic, is a country in Southeast Europe. Located on the southern tip of the Balkan peninsula, it shares land borders with Albania to the northwest, North Macedonia and Bulgaria to the north, and Turkey to th ...

is at best only circumstantial. What is certain is that the variability of Mira was recorded by the astronomer David Fabricius beginning on August 3, 1596. Observing what he thought was the planet Mercury (later identified as

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

), 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. Fabricius assumed it was a nova, but then saw it again on February 16, 1609. In 1638 Johannes Holwarda determined a period of the star's reappearances, eleven months; he is often credited with the discovery of Mira's variability.

was observing it at the same time and named it Mira in 1662, for it acted like no other known star. Ismail Bouillaud then estimated its period at 333 days, less than one day off the modern value of 332 days. Bouillaud's measurement may not have been erroneous: Mira is known to vary slightly in period, and may even be slowly changing over time. The star is estimated to be a six-billion-year-old red giant. Mira the star

There is considerable speculation as to whether Mira had been observed prior to Fabricius. Certainly

'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. Karl Manitius, a modern translator of

Hipparchus Hipparchus (; , ; BC) was a Ancient Greek astronomy, Greek astronomer, geographer, and mathematician. He is considered the founder of trigonometry, but is most famous for his incidental discovery of the precession of the equinoxes. Hippar ...

' ''Commentary on Aratus'', has suggested that certain lines from that second-century text may be about Mira. The other pre-telescopic Western catalogs of

Ptolemy Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...

, al-Sufi,

Ulugh Beg Mīrzā Muhammad Tarāghāy bin Shāhrukh (; ), better known as Ulugh Beg (; 22 March 1394 – 27 October 1449), was a Timurid sultan, as well as an astronomer and mathematician. Ulugh Beg was notable for his work in astronomy-related ma ...

and

Tycho Brahe Tycho Brahe ( ; ; born Tyge Ottesen Brahe, ; 14 December 154624 October 1601), generally called Tycho for short, was a Danish astronomer of the Renaissance, known for his comprehensive and unprecedentedly accurate astronomical observations. He ...

turn up no mentions, even as a regular star. 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. An estimate obtained in 1925 from interferometry by Francis G. Pease at the

Mount Wilson Observatory The Mount Wilson Observatory (MWO) is an Observatory#Astronomical observatories, astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson (California), Mount Wilson, a peak in the San Gabrie ...

gave Mira a diameter of 250-260 million miles (402 to 418 million km, or approximately ), making it the then-second largest star known and comparable to historical estimates of

Betelgeuse Betelgeuse is a red supergiant star in the constellation of Orion (constellation), Orion. It is usually the List of brightest stars, tenth-brightest star in the night sky and, after Rigel, the second brightest in its constellation. It i ...

, surpassed only by

Antares Antares is the brightest star in the constellation of Scorpius. It has the Bayer designation α Scorpii, which is Latinisation of names, Latinised to Alpha Scorpii. Often referred to as "the heart of the scorpion", Antares is flanked by ...

. On the contrary, Otto Struve thought of Mira as a red supergiant with an approximate radius of , while modern consensus accepts Mira to be a highly evolved

asymptotic giant branch The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) lat ...

star.

Distance and background Information

Pre-''

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions and distances of ...

'' estimates centered on 220

s; while Hipparcos data from the 2007 reduction suggest a distance of 299 light-years, with a

margin of error The margin of error is a statistic expressing the amount of random sampling error in the results of a Statistical survey, survey. The larger the margin of error, the less confidence one should have that a poll result would reflect the result of ...

of 11%. The age of Mira is suspected to be about 6 billion years old. Its gaseous material is scattered, as much as one-thousandth as thin as the air around us. Mira is also among the coolest known bright stars of the red giant class, with a temperature ranging from 3,000 to 4,000 degrees Fahrenheit (1,600 to 2,200 degrees Celsius). As with other long-period variables, Mira's deep red color at minimum pales to a lighter orange as the star brightens. Within the next few million years, Mira will discard its outer layers and become a planetary nebula, leaving behind a white dwarf.

Stellar system

This binary star system consists of a red giant (Mira, designated Mira A) undergoing mass loss and a high-temperature

companion (Mira B) that is accreting mass from the primary. Such an arrangement of stars is known as a symbiotic system and this is the closest such symbiotic pair to the

. Examination of this system by the

Chandra X-ray Observatory The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources ...

shows a direct mass exchange along a bridge of matter from the primary to the white dwarf. The two stars are currently separated by about 70

astronomical unit The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...

Component A

Mira A is currently an

(AGB) star, in the thermally pulsing AGB phase. Each pulse lasts a decade or more, and an amount of time 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. 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 Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

band by the

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

have shown a plume-like feature pointing toward the companion star.

Variability

Mira A is a

, specifically the prototypical

. The 6,000 to 7,000 known stars of this classGCVS: vartype.txt
from the GCVS catalogue (statistics at the end of the file indicate 6,006 confirmed and 1,237 probable Mira variables) are all red giants whose surfaces pulsate in such a way as to increase and decrease in brightness over periods ranging from about 80 to more than 1,000 days. In the particular case of Mira, its increases in brightness take it up to about magnitude 3.5 on average, placing it among the brighter stars in the Cetus constellation. 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 1,700 times. Mira emits the vast majority of its

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes: * ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infr ...

in the

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

, and its variability in that band is only about two magnitudes. The shape of its

light curve In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...

is of an increase over about 100 days, and the return to minimum taking twice as long. Contemporary approximate maxima for Mira: * Oct 21–31, 1999 * Sep 21–30, 2000 * Aug 21–31, 2001 * Jul 21–31, 2002 * Jun 21–30, 2003 * May 21–31, 2004 * Apr 11–20, 2005 * Mar 11–20, 2006 * Feb 1–10, 2007 * Jan 21–31, 2008 * Dec 21–31, 2008 * Nov 21–30, 2009 * Oct 21–31, 2010 * Sep 21–30, 2011 * Aug 27, 2012 * Jul 26, 2013 * May 12, 2014 * Apr 9, 2015 * Mar 6, 2016 * Jan 31, 2017 * Dec 29, 2017 * Nov 26, 2018 * Oct 24, 2019 * Sep 20, 2020 * Aug 18, 2021 * Jul 16, 2022 * Jun 13, 2023 * May 10, 2024 Chi Cygni pulsations

From northern temperate latitudes, Mira is generally not visible between late March and June due to its proximity to the Sun. This means that at times several years can pass without it appearing as a naked-eye object. The pulsations of Mira variables cause the star to expand and contract, but also to change its temperature. The temperature is highest slightly after the visual maximum, and lowest slightly before minimum. The photosphere, measured at the Rosseland radius, is smallest just before visual maximum and close to the time of maximum temperature. The largest size is reached slightly before the time of lowest temperature. The bolometric luminosity is proportional to the fourth power of the temperature and the square of the radius, but the radius varies by over 20% and the temperature by less than 10%. In Mira, the highest luminosity occurs close to the time when the star is hottest and smallest. The visual magnitude is determined both by the luminosity and by the proportion of the

that occurs at visual wavelengths. Only a small proportion of the radiation is emitted at visual wavelengths and this proportion is very strongly influenced by the temperature ( Planck's law). Combined with the overall luminosity changes, this creates the very big

visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

variation with the maximum occurring when the temperature is high.

Infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

VLTI measurements of Mira at phases 0.13, 0.18, 0.26, 0.40 and 0.47, show that the radius varies from at phase 0.13 just after maximum to at phase 0.40 approaching minimum. The temperature at phase 0.13 is and at phase 0.26 about halfway from maximum to minimum. The luminosity is calculated to be at phase 0.13 and at phase 0.26. The pulsations of Mira have the effect of expanding its photosphere by around 50% compared to a non-pulsating star. In the case of Mira, if it was not pulsating it is modelled to have a radius of only around .

Mass loss

Ultraviolet studies of Mira by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

's Galaxy Evolution Explorer ( GALEX) space telescope have revealed that it sheds a trail of material from the outer envelope, leaving a tail 13 light-years in length, formed over tens of thousands of years. It is thought that a hot

bow wave A bow wave is the wave that forms at the bow (watercraft), bow of a ship when it moves through the water. As the bow wave spreads out, it defines the outer limits of a ship's Wake (physics), wake. A large bow wave slows the ship down, is a risk t ...

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 interstellar space, through which Mira is moving at an extremely high speed of . The tail consists of material stripped from the head of the bow wave, which is also visible in ultraviolet observations. Mira's bow shock will eventually evolve into a

planetary nebula A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelated to planets. The ...

, the form of which will be considerably affected by the motion through the

interstellar medium The interstellar medium (ISM) is the matter and radiation that exists in the outer space, space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as cosmic dust, dust and cosmic rays. It f ...

(ISM). Mira’s tail offers a unique opportunity to study how stars like our sun die and ultimately seed new solar systems. As Mira hurls along, its tail drops off carbon, oxygen and other important elements needed for new stars, planets, and possibly even life to form. This tail material, visible now for the first time, has been shed over the past 30,000 years. Mira the star-by Nasa alt crop

Component B

The companion star is away from the main star. It was resolved by the

in 1995, when it was 70

s from the primary; and results were announced in 1997. 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 companion's

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

around Mira is approximately 400 years. In 2007, observations showed a protoplanetary disc around the companion, Mira B. This disc is being accreted from material in the

solar wind The solar wind is a stream of charged particles released from the Sun's outermost atmospheric layer, the Stellar corona, corona. This Plasma (physics), plasma mostly consists of electrons, protons and alpha particles with kinetic energy betwee ...

from Mira and could eventually form new planets. These observations also hinted that the companion was a main-sequence star of around 0.7

solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...

and

spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

K, instead of a white dwarf as originally thought. However, in 2010 further research indicated that Mira B is, in fact, a white dwarf.

References

External links

Speeding Bullet Star Leaves Enormous Streak Across Sky
at

Caltech The California Institute of Technology (branded as Caltech) is a private university, private research university in Pasadena, California, United States. The university is responsible for many modern scientific advancements and is among a small g ...

Mira has tail nearly 13 light years in length (BBC)
* Astronomy Picture of the Day:
1998-10-11

*
lightcurve
of Mira from the BAV. * Universe Today
That's Not a Comet, that's a Star

OMICRON CETI (Mira)

Winter 2006: Mira revisited
{{Sky, 02, 19, 20.792, -, 02, 58, 39.50 Ceti, Omicron Binary stars Cetus Mira variables M-type giants Stars with proper names Ceti, 68 010826 0681 014386 Emission-line stars Durchmusterung objects