The Trapezium or Orion Trapezium Cluster, also known by its
Bayer designation
A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. ...
of Theta
1 Orionis, is a tight
open cluster of
star
A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
s in the heart of the
Orion Nebula
The Orion Nebula (also known as Messier 42, M42, or NGC 1976) is a diffuse nebula situated in the Milky Way, being south of Orion's Belt in the constellation of Orion. It is one of the brightest nebulae and is visible to the naked eye in the nig ...
, 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 origins of the e ...
of
Orion. It was discovered by
Galileo Galilei. On 4 February 1617 he sketched three of the stars (
A,
C and
D), but missed the surrounding nebulosity.
[Galileo Galilei: Siderius Nuncius, ]Venice
Venice ( ; it, Venezia ; vec, Venesia or ) is a city in northeastern Italy and the capital of the Veneto Regions of Italy, region. It is built on a group of 118 small islands that are separated by canals and linked by over 400 ...
, 1610. English Translation published at Bard College, Hudson NY" October 9, 2003 English Translatio
Original Latin versio
/ref>[Tom Pope and Jim Mosher: Galilean telescope homepage" March 17, 2006 , "Some have expressed puzzlement that in his text Galileo does not mention the nebulosity (known in modern nomenclature as M42) enveloping these stars. ... Galileo believed, as he explains in ''Sidereus Nuncius'', that what looks nebulous to the eye is resolved into stars by his telescope; what looks nebulous through his telescope could presumably also be resolved into stars by a still larger and more powerful telescope. Hence, a diffuse glow would be, more than anything, an indication of the limitations of his telescope and not particularly worthy of special note."][Tom Pope and Jim Mosher: Page on Galileo's February 4, 1617 notebook drawing of the Trapezium region, May 2, 2006 "Perhaps significantly, Galileo makes no mention of having noticed the now well-known gas cloud, M42, surrounding the Trapezium stars]
A fourth component ( Theta1 Orionis B, B) was identified by several observers in 1673, and several more components were discovered later like E, for a total of eight by 1888. Subsequently, several of the stars were determined to be binaries. Telescopes of amateur astronomers from about aperture can resolve six stars under good seeing
Seeing may refer to:
* Visual perception
* Astronomical seeing, the blurring effects of air turbulence in the atmosphere
* In the occult seeing refers to "the sight" or the ability to see auras or to predict the future; see fortune-telling
* ' ...
conditions.
The Trapezium is a relatively young cluster that has formed directly out of the parent nebula. The five brightest stars are on the order of 15 to 30 solar mass
The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...
es in size. They are within a diameter of 1.5 light-year
A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...
s of each other and are responsible for much of the illumination of the surrounding nebula. The Trapezium may be a sub-component of the larger Orion Nebula Cluster, a grouping of about 2,000 stars within a diameter of 20 light-years.
Identification
The Trapezium is most readily identifiable by the asterism of four relatively bright stars for which it is named. The four are often identified as A, B, C and D in order of increasing right ascension
Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the (hour circle of the) point in question above the earth.
When paired w ...
. The brightest of the four stars is C, or Theta1 Orionis C, with an apparent magnitude of 5.13. Both A and B have been identified as eclipsing binaries.
Infrared images of the Trapezium are better able to penetrate the surrounding clouds of dust, and have located many more stellar components. About half the stars within the cluster have been found to contain evaporating circumstellar disks, a likely precursor to planetary formation. In addition, brown dwarfs and low-mass runaway stars have been identified.
Possible black hole
A 2012 paper suggests an intermediate-mass black hole with a mass more than 100 times that of the Sun may be present within the Trapezium, something that could explain the large velocity dispersion of the stars of the cluster.stellar wind
A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric.
D ...
s collide with existing interstellar material
File:Trapezium Labeled.jpg, A wider shot of the core details showing the trapezium in context of the surrounding nebulae
File:Great Nebula in Orion Labeled.jpg, Core detail of the nebula with all the stars identified
References
Further reading
*
*
External links
Chandra Observatory Uncovers Hot Stars In The Making
MIT Press Release, 2000.
* Astronomy Picture of the Day
In the Center of the Trapezium
2003 March 2
Observing the Trapezium
{{DEFAULTSORT:Trapezium Cluster
Open clusters
Orion (constellation)
Orion molecular cloud complex
Orionis, Theta1
Asterisms (astronomy)
BD-05 1315
Orionis, 41