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Trapezium (astronomy)
Encyclopedia
The Trapezium, or Orion Trapezium Cluster is a tight open cluster
of star
s in the heart of the Orion Nebula
, in the constellation
of Orion
. It was discovered by Galileo Galilei
. On February 4, 1617 he sketched three of the stars (A, C, D), but missed the surrounding nebulosity. The fourth component (B) was identified by several observers in 1673, and several more components were discovered later, for a total of eight by 1888. Subsequently several of the stars were determined to be binaries. Telescopes of amateur astronomers from about 5 inch aperture
can resolve six stars under good seeing
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 15-30 solar mass
es in size. They are within a diameter of 1.5 light-year
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.
of four relatively bright stars. The four are often identified as A, B, C, and D in order of increasing right ascension
. 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 dwarf
s and low-mass runaway stars have been identified.
Open cluster
An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy, and many more are thought to exist...
of star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s in the heart of the Orion Nebula
Orion Nebula
The Orion Nebula is a diffuse nebula situated south of Orion's Belt. It is one of the brightest nebulae, and is visible to the naked eye in the night sky. M42 is located at a distance of and is the closest region of massive star formation to Earth. The M42 nebula is estimated to be 24 light...
, in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Orion
Orion (constellation)
Orion, often referred to as The Hunter, is a prominent constellation located on the celestial equator and visible throughout the world. It is one of the most conspicuous, and most recognizable constellations in the night sky...
. It was discovered by Galileo Galilei
Galileo Galilei
Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...
. On February 4, 1617 he sketched three of the stars (A, C, D), but missed the surrounding nebulosity. The fourth component (B) was identified by several observers in 1673, and several more components were discovered later, for a total of eight by 1888. Subsequently several of the stars were determined to be binaries. Telescopes of amateur astronomers from about 5 inch aperture
Aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...
can resolve six stars under good seeing
Astronomical seeing
Astronomical seeing refers to the blurring and twinkling of astronomical objects such as stars caused by turbulent mixing in the Earth's atmosphere varying the optical refractive index...
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 15-30 solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
es in size. They are within a diameter of 1.5 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
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
It is most readily identifiable by the asterismAsterism (astronomy)
In astronomy, an asterism is a pattern of stars recognized on Earth's night sky. It may form part of an official constellation, or be composed of stars from more than one. Like constellations, asterisms are in most cases composed of stars which, while they are visible in the same general direction,...
of four relatively bright stars. The four are often identified as A, B, C, and D in order of increasing 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. The other coordinate is the declination.-Explanation:...
. 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
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
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 dwarf
Brown dwarf
Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
s and low-mass runaway stars have been identified.
External links
- Chandra Observatory Uncovers Hot Stars In The Making, MIT Press Release, 2000.
- A detailed description of the Trapezium Cluster
- Astronomy Picture of the DayAstronomy Picture of the DayAstronomy Picture of the Day is a website provided by NASA and Michigan Technological University . According to the website, "Each day a different image or photograph of our universe is featured, along with a brief explanation written by a professional astronomer."The photograph is not necessarily...
- In the Center of the Trapezium 2003 March 2