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7 Iris ( , or as in ) is a large main belt asteroid. Among S-type asteroid
S-type asteroid

S-type asteroids are of a silicaceous composition, hence the name. Approximately 17% of asteroids are of this type, making it the second most common after the C-type asteroid....
s it ranks fifth in geometric mean
Geometric mean

The geometric mean, in mathematics, is a type of mean or average, which indicates the central tendency or typical value of a set of numbers. It is similar to the arithmetic mean, which is what most people think of with the word "average," except that instead of adding the set of numbers and then dividing the sum by the count of numbers in the...
 diameter after Eunomia
15 Eunomia

'15 Eunomia' is a very large asteroid in the inner asteroid belt. It is the largest of the stony asteroids, and somewhere between the 8th to 12th largest Main Belt asteroid overall ....
, Juno
3 Juno

Juno , formal designation 3 Juno in the Minor Planet Center catalogue system, was the third asteroid to be discovered and is one of the larger main belt asteroids, being one of the two largest stony asteroids, along with 15 Eunomia....
, Amphitrite
29 Amphitrite

'29 Amphitrite' is one of the largest S-type asteroids, probably third in diameter after 15 Eunomia and 3 Juno, although 7 Iris and 532 Herculina are similar in size....
 and Herculina
532 Herculina

532 Herculina is a very large asteroid, with a diameter of around 225 km....
.

Its bright surface and small distance from the Sun make Iris the fourth brightest object in the asteroid belt
Asteroid belt

The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets....
 after Vesta
4 Vesta

4 Vesta is the second most massive object in the asteroid belt, with a mean diameter of about 530 km and an estimated mass of 9% of the mass of the entire asteroid belt....
, Ceres, and Pallas
2 Pallas

'2 Pallas' is one of the largest asteroids and is located in the main asteroid belt. It was the second asteroid to be discovered, by astronomy Heinrich Wilhelm Matth?us Olbers on March 28, 1802....
. But at typical opposition
Opposition (astronomy)

Opposition is a term used in positional astronomy and astrology to indicate when one Astronomical object is on the opposite side of the sky when viewed from a particular place ....
s it marginally outshines the larger though darker Pallas
2 Pallas

'2 Pallas' is one of the largest asteroids and is located in the main asteroid belt. It was the second asteroid to be discovered, by astronomy Heinrich Wilhelm Matth?us Olbers on March 28, 1802....
. It has a mean
Mean

In statistics, mean has two related meanings:* the arithmetic mean .* the expected value of a random variable, which is also called the population mean....
 opposition magnitude
Apparent magnitude

The apparent magnitude of a celestial body is a measurement of its brightness as seen by an observer on Earth, normalized to the value it would have in the absence of the Earth's atmosphere....
 of +7.8, comparable to that of Neptune
NEPTUNE

=Overview=The project, along with sister project, VENUS, offers a unique approach to ocean science. Traditionally, ocean scientists have relied on infrequent ship cruises or space-based satellites to carry out their research....
, and can easily be seen with binoculars
Binoculars

Binocular telescopes, or binoculars , are two identical or mirror-symmetry optical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes when viewing distant objects....
 at most oppositions.






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7 Iris ( , or as in ) is a large main belt asteroid. Among S-type asteroid
S-type asteroid

S-type asteroids are of a silicaceous composition, hence the name. Approximately 17% of asteroids are of this type, making it the second most common after the C-type asteroid....
s it ranks fifth in geometric mean
Geometric mean

The geometric mean, in mathematics, is a type of mean or average, which indicates the central tendency or typical value of a set of numbers. It is similar to the arithmetic mean, which is what most people think of with the word "average," except that instead of adding the set of numbers and then dividing the sum by the count of numbers in the...
 diameter after Eunomia
15 Eunomia

'15 Eunomia' is a very large asteroid in the inner asteroid belt. It is the largest of the stony asteroids, and somewhere between the 8th to 12th largest Main Belt asteroid overall ....
, Juno
3 Juno

Juno , formal designation 3 Juno in the Minor Planet Center catalogue system, was the third asteroid to be discovered and is one of the larger main belt asteroids, being one of the two largest stony asteroids, along with 15 Eunomia....
, Amphitrite
29 Amphitrite

'29 Amphitrite' is one of the largest S-type asteroids, probably third in diameter after 15 Eunomia and 3 Juno, although 7 Iris and 532 Herculina are similar in size....
 and Herculina
532 Herculina

532 Herculina is a very large asteroid, with a diameter of around 225 km....
.

Its bright surface and small distance from the Sun make Iris the fourth brightest object in the asteroid belt
Asteroid belt

The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets....
 after Vesta
4 Vesta

4 Vesta is the second most massive object in the asteroid belt, with a mean diameter of about 530 km and an estimated mass of 9% of the mass of the entire asteroid belt....
, Ceres, and Pallas
2 Pallas

'2 Pallas' is one of the largest asteroids and is located in the main asteroid belt. It was the second asteroid to be discovered, by astronomy Heinrich Wilhelm Matth?us Olbers on March 28, 1802....
. But at typical opposition
Opposition (astronomy)

Opposition is a term used in positional astronomy and astrology to indicate when one Astronomical object is on the opposite side of the sky when viewed from a particular place ....
s it marginally outshines the larger though darker Pallas
2 Pallas

'2 Pallas' is one of the largest asteroids and is located in the main asteroid belt. It was the second asteroid to be discovered, by astronomy Heinrich Wilhelm Matth?us Olbers on March 28, 1802....
. It has a mean
Mean

In statistics, mean has two related meanings:* the arithmetic mean .* the expected value of a random variable, which is also called the population mean....
 opposition magnitude
Apparent magnitude

The apparent magnitude of a celestial body is a measurement of its brightness as seen by an observer on Earth, normalized to the value it would have in the absence of the Earth's atmosphere....
 of +7.8, comparable to that of Neptune
NEPTUNE

=Overview=The project, along with sister project, VENUS, offers a unique approach to ocean science. Traditionally, ocean scientists have relied on infrequent ship cruises or space-based satellites to carry out their research....
, and can easily be seen with binoculars
Binoculars

Binocular telescopes, or binoculars , are two identical or mirror-symmetry optical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes when viewing distant objects....
 at most oppositions. At rare oppositions near perihelion Iris can reach a magnitude of +6.7, which is as bright as Ceres ever gets, and reports of it being seen without optical aid are unverified.

Discovery and name

It was the seventh asteroid
Asteroid

Asteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun, smaller than planets but larger than meteoroids....
 discovered, on August 13, 1847 by J. R. Hind
John Russell Hind

John Russell Hind Fellow of the Royal Society was an England astronomer. Some sources give his name as John Russel Hind with only one "L"....
 from London
London

London is the capital of both England and the United Kingdom, and the most populous municipality in the European Union. An important settlement for two millennia, History of London goes back to its founding by the Roman Empire....
, UK
United Kingdom

The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom , the UK or Britain,is a sovereign state located off the northwestern coast of continental Europe....
. It was Hind's first asteroid discovery.

Iris was named after the rainbow
Rainbow

A rainbow is an optics and meteorology phenomenon that causes a optical spectrum of light to appear in the sky when the Sun shines onto droplets of moisture in the Earth's atmosphere....
 goddess Iris
Iris (mythology)

In Greek mythology, Iris is the personification of the rainbow and messenger of the gods. As the sun unites Earth and heaven, Iris links the gods to humanity....
 of Greek mythology
Greek mythology

Greek mythology is the body of myths and legends belonging to the Ancient Greece concerning their List of Greek mythological figures#Immortals and Greek hero cult, Cosmology#Metaphysical cosmology, and the origins and significance of their own cult and ritual practices....
, sister of the Harpies and messenger of the gods, especially Hera
Hera

In the Twelve Olympians of classical Greek Mythology, Hera or Here was the wife and older sister of Zeus. Her chief function was as goddess of women and marriage....
. Her quality of attendant of Hera was particularly appropriate to the circumstances of discovery, as she was spotted following 3 Juno
3 Juno

Juno , formal designation 3 Juno in the Minor Planet Center catalogue system, was the third asteroid to be discovered and is one of the larger main belt asteroids, being one of the two largest stony asteroids, along with 15 Eunomia....
 (Juno
Juno (mythology)

File:Juno sospita pushkin.jpgJuno was an Roman religion, the protector and special counselor of the state. She is a daughter of Saturn and sister of the chief god Jupiter and the mother of Juventas, Mars , and Vulcan ....
 is the Roman
Roman mythology

Roman mythology, or more appropriately, Latin mythology, refers to the mythology beliefs of the Italic people inhabiting the region of Latium and its main city, Rome....
 equivalent of Hera) by less than an hour of right ascension
Right ascension

Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system....
.

According to the OED
Oxford English Dictionary

The Oxford English Dictionary , published by the Oxford University Press , is a comprehensive dictionary of the English language. Two fully-bound print editions of the OED have been published under its current name, in 1928 and 1989; as of December 2008 the dictionary's current editors have completed a quarter of the third edition....
, the correct adjectival form
Adjective

In grammar, an adjective is a word whose main syntax role is to grammatical modifier a noun or pronoun, giving more information about the noun or pronoun's definition....
 of the name is Iridian.

Characteristics

Lightcurve analysis indicates a somewhat angular shape and that Iris' pole points towards ecliptic coordinates
Ecliptic coordinate system

The ecliptic coordinate system is a celestial coordinate system that uses the ecliptic for its fundamental plane. The ecliptic is the path that the sun appears to follow across the sky over the course of a year....
 (ß, ?) = (10°, 20°) with a 10° uncertainty. This gives an axial tilt
Axial tilt

In astronomy, axial tilt is the inclination angle of a planet axis of rotation in relation to its Orbital plane . It is also called axial inclination or obliquity....
 of 85°, so that on almost a whole hemisphere of Iris, the sun does not set during summer, and does not rise during winter. On an airless body this gives rise to very large temperature differences.

Iris' surface likely exhibits albedo
Albedo

The albedo of an object is the extent to which it diffusely reflects light from the Sun. It is therefore a more specific form of the term reflectivity....
 differences, with possibly a large bright area in the northern hemisphere.

The surface of Iris is overall very bright and is probably a mixture nickel
Nickel

Nickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge....
-iron
Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
 metal
Metal

In chemistry, a metal is a chemical element whose atoms readily lose electrons to form positive ions , and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms....
s and magnesium
Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, atomic weight 24.3050 and common oxidation number +2.Magnesium, an alkaline earth metal, is the ninth most abundance of the chemical elements in the universe by mass....
- and iron
Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
-silicate
Silicate

A silicate is a compound containing an anion in which one or more central silicon atoms are surrounded by electronegative ligands. This definition is broad enough to include species such as hexafluorosilicate , [SiF6]2-, but the silicate species that are encountered most often consist of silicon with oxygen as the ligand...
s. Its spectrum is similar to that of L
L chondrite

The L type ordinary chondrites are the second most common type of meteorite, accounting for approximately 35% of all those catalogued, and 40% of the ordinary chondrites....
 and LL chondrite
LL chondrite

The LL chondrites are the least abundant group of the ordinary chondrites, accounting for about 10-11% of observed ordinary-chondrite falls and 8-9% of all meteorite falls ....
s with corrections for space weathering
Space weathering

Space weathering is a blanket term used for a number of processes that act on any body exposed to the harsh space environment. Airless bodies incur many weathering processes:...
, so it may be an important contributor of these meteorites. Planetary dynamics also indicates that it should be a significant source of meteorites.

Iris was observed occulting
Occultation

An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy and can also be used in a general sense to describe when an object in the foreground occults objects in the background....
 a star
Star

A star is a massive, luminous ball of Plasma that is held together by its own gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth....
 on May 26, 1995 and later on July 25, 1997. Both observations gave a diameter
Diameter

In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle....
 of about 200 km.

External links

— Horizons can be used to obtain a current ephemeris.