Triangulum Constellation

Triangulum constellation is located in the northern sky. Its name means “the triangle” in Latin.

Triangulum was one of the 48 constellations catalogued by the Greek astronomer Ptolemy in the 2nd century.

It does not have any first magnitude stars.

The three brightest stars in the constellation form the shape of a long, narrow triangle.

The constellation is home to the Triangulum Galaxy (Messier 33), one of the best known galaxies in the night sky.


triangulum constellation,triangulum stars,triangulum star map,triangulum location
Triangulum Constellation Map, by IAU and Sky&Telescope magazine
Triangulum is the 78th constellation in size, occupying an area of 132 square degrees.

It lies in the first quadrant of the northern hemisphere (NQ1) and can be seen at latitudes between +90° and -60°.

The neighboring constellations are Andromeda, Aries, Perseus and Pisces.

Triangulum has one star with a confirmed planet and contains one Messier object, Messier 33 (M33, NGC 598, Triangulum Galaxy).

The brightest star in the constellation is Beta Trianguli, with an apparent visual magnitude of 3.00.

There are no meteor showers associated with the constellation.

Triangulum belongs to the Perseus family of constellations, along with Andromeda, Auriga, Cassiopeia, Cepheus, Cetus, Lacerta, Pegasus and Perseus.


The Greeks knew the constellation as Deltoton, named for its shape, which resembled the capital Greek letter delta. Eratosthenes said that the constellation represented the delta of the river Nile, and Hyginus wrote that some people saw it as the island of Sicily. Sicilia was one of the early names for the constellation because Ceres, who was the patron goddess of the island, was said to have begged Jupiter to place the island in the sky.

The Babylonians saw Triangulum and the star Gamma Andromedae in Andromeda constellation as a constellation called MUL.Apin, or the Plough.

The Polish astronomer Johannes Hevelius introduced a smaller triangle, Triangulum Minus, in 1687, formed by three stars located near Triangulum, but the division soon fell into disuse.


β Trianguli (Beta Trianguli)

Beta Trianguli is the brightest star in Triangulum constellation. It has an apparent visual magnitude of 3.00 and is approximately 127 light years distant from Earth.

Beta Trianguli is a white giant star with the stellar classification of A5III. It is thought to be a spectroscopic binary star with components separated by less than 5 astronomical units and orbiting each other with a period of 31.39 days.

Beta Trianguli is a source of excess infrared radiation, which suggests that the stars have a ring of dust orbiting them at a distance of 10 to 20 astronomical units.

Caput Trianguli (Ras al Muthallah) – α Trianguli (Alpha Trianguli)

Alpha Trianguli is the second brightest star in Triangulum. It has an apparent magnitude of 3.42 and is 63.3 light years distant from Earth. It is a very close binary star system, one in which individual stars cannot be resolved. The stars complete an orbit around their centre of mass every 1.736 days. The system is believed to be about 1.6 billion years old.

The primary component in the system is either a subgiant or giant star and the combined stellar classification for the system ranges from F5III to F6IV. The primary star is a rapid rotator and, as a result, it has the shape of an oblate spheroid. When observed from Earth, the star’s ellipsoidal profile varies over the course of an orbit, which in turn causes variations in the star’s luminosity. The star is classified as an ellipsoidal variable.

The traditional name of Alpha Trianguli, Ras al Muthallah, comes from the Arabic ra’s al-muθallaθ, which means “the head of the triangle.” The star is also sometimes known by its Latin name, Caput Trianguli, which has the same meaning.

γ Trianguli (Gamma Trianguli)

Gamma Trianguli is the third brightest star in the constellation. It has an apparent visual magnitude of 4.01 and is 112.3 light years distant from Earth. It lies along the same line of sight as Delta Trianguli and 7 Trianguli and forms an optical triple star with them.

Gamma Trianguli is a white main sequence star belonging to the stellar class A1Vnn. It has a mass 2.7 times that of the Sun and almost twice the solar radius. It is about 33 times more luminous than the Sun. The star is believed to be about 300 million years old.

Gamma Trianguli is also a rapid rotator, with a projected rotational velocity of 254 km/s, and, like Alpha Trianguli, it has the shape of an oblate spheroid. It has a debris disk orbiting it and, as a result, it is a source of infrared radiation.

δ Trianguli (Delta Trianguli)

Delta Trianguli is another spectroscopic binary in Triangulum. It has a visual magnitude of 4.865 and is only 35.2 light years distant from Earth.

The system is composed of a yellow dwarf belonging to the stellar class G0V and an orange dwarf with an estimated spectral class ranging from G9V to K4V. The stars orbit their centre of mass with an estimated separation of 0.106 astronomical units. They complete an orbit every 10.02 days.

6 Trianguli – ι Trianguli (Iota Trianguli)

6 Trianguli is a quadruple star system in Triangulum. It has an apparent visual magnitude of 4.49 and is approximately 305 light years distant from Earth. The system has the stellar classification F5V.

6 Trianguli consists of a fifth magnitude G5 giant and a magnitude 6.44 F5 dwarf, separated by 3.8 arcseconds. 6 Triangulum A, the class G giant, is itself a binary star with a class F5 dwarf companion orbiting it every 14.732 days. The giant and the dwarf are 65 and 32 times more luminous than the Sun respectively.

6 Triangulum B, the other pair, is believed to consist of a pair of class F stars with an orbital period of 2.24 days and luminosities of 18 and 9 times solar. The stars are separated by only 0.05 astronomical units.

6 Trianguli has the variable designation TZ Trianguli and is classified as an RS Canum Venaticorum type variable, which is to say a close binary star with an active chromosphere that causes large stellar spots, which in turn cause variations in luminosity.

6 Trianguli used to be the main star in a modern subdivision of ancient Triangulum, which was known as Triangulum Minoris, or “the smaller triangle.” Triangulum Minoris was created in the 1600s and was formed by the stars 6, 10 and 12 Trianguli.

ε Trianguli (Epsilon Trianguli)

Epsilon Trianguli is a binary star system with an apparent visual magnitude of 5.50. It is approximately 390 light years distant from Earth.

The primary component in the system is a white dwarf belonging to the spectral class A5 V, believed to be about 600 million years old. The star has a radius three times solar. The secondary star has a visual magnitude of 11.4 and lies at a separation of 3.9 seconds of arc from the primary star. The primary component is believed to have a dusty disk in orbit because it emits excess infrared radiation.

Epsilon Trianguli is a suspected member of the Ursa Major Moving Group of stars that share a common motion through space.

HD 13189

HD 13189 is an evolved orange giant with the stellar classification K1II-III. It has an apparent visual magnitude of 7.57 and is approximately 1,800 light years distant from Earth. It has 2-7 times the Sun’s mass and is about 3,980 times more luminous than the Sun.

In 2005, a brown dwarf or planetary companion was discovered orbiting the star. The companion, HD 13189 b, has a mass 8 to 20 times that of Jupiter and completes an orbit around the star every 472 days from a separation of 1.85 astronomical units.

HD 9446

HD 9446 is a yellow main sequence dwarf with an apparent magnitude of 8.35. The star is approximately 171 light years distant from Earth. It has the same mass and radius as the Sun and roughly the same luminosity.

Two planets were discovered in the star’s orbit in January 2010. HD 9446 b has a mass 0.7 times that of Jupiter and orbits the star every 30.052 days, and HD 9446 c has 1.82 Jupiter masses and completes an orbit around the star every 192.9 days.


m33,spiral galaxy
Triangulum Galaxy (Messier 33), image: Hewholooks at
Triangulum Galaxy – Messier 33 (M33, NGC 598)

The Triangulum Galaxy is a spiral galaxy in Triangulum. It is one of the most distant deep sky objects that can be seen without binoculars.

The galaxy has an apparent visual magnitude of 5.72 and is between 2,380 and 3,070 thousand light years distant from Earth.

Messier 33 is the third largest member of the Local Group of galaxies, after the Milky Way and Andromeda Galaxy. It is about 50,000 light years in diameter and contains about 40 billion stars. (For comparison, the Milky Way has about 400 billion and Andromeda about a trillion stars.)

black hole,triangulum galaxy
The main component of this graphic is an artist’s representation of M33 X-7, a binary system in the nearby galaxy M33. In this system, a star about 70 times more massive than the Sun (large blue object) is revolving around a black hole. This black hole is almost 16 times the Sun’s mass, a record for black holes created from the collapse of a giant star. Other black holes at the centers of galaxies are much more massive, but this object is the record-setter for a so-called “stellar mass” black hole.
In the illustration, an orange disk surrounds the black hole. This depicts material, fed by a wind from the blue companion star, which has been swept into orbit around the black hole. Rather than flowing unimpeded and uniformly into space, wind from the star is pulled towards the black hole by its powerful gravity. The wind that does make it past the black hole is disrupted, causing turbulence and ripples beyond the disk. The companion star itself is also distorted by the gravity from the black hole. The star is stretched slightly in the direction of the black hole, causing it to become less dense in this region and to appear darker.
The inset shows a composite of data from NASA’s Chandra X-ray Observatory (blue) and the Hubble Space Telescope. The bright objects in the inset image are young, massive stars around M33 X-7, and the bright, blue Chandra source is M33 X-7 itself. X-rays from Chandra reveals how long the black hole is eclipsed by the companion star, which indicates the size of the companion. Observations by the Gemini telescope on Mauna Kea, Hawaii track the orbital motion of the companion around the black hole, giving information about the mass of the two members of the binary. Other observed properties of the binary were also used to help constrain the mass estimates of both the black hole and its companion. Illustration: NASA, CXC, M.Weiss; X-ray: NASA, CXC, CfA, P.Plucinsky et al.; Optical: NASA, STScI, SDSU, J.Orosz et al.
The galaxy is also home to at least 54 globular clusters.

The Triangulum Galaxy contains the largest stellar mass black hole (a black hole formed by the gravitational collapse of a massive star) known.

The black hole, M33 X-7, was discovered in 2007 and has about 15.7 times the mass of the Sun. It orbits a companion star and eclipses it every 3.45 days. The total mass of the binary system is about 85.7 times that of the Sun. The companion star has a mass about 70 times solar, which makes it the most massive companion star known in a binary system containing a black hole.

A stream of hydrogen gas linking Triangulum to the Andromeda Galaxy was discovered in 2004 and confirmed in 2011. This suggests that the two galaxies have tidally interacted in the past.

The Pisces Dwarf, another galaxy in the Local Group, is located 913,000 light years from both galaxies and could be a satellite galaxy of either Triangulum or Andromeda Galaxy.

The Triangulum Galaxy is sometimes also referred to as the Pinwheel Galaxy, but this name is formally used for Messier 101 in Ursa Major constellation.

The Triangulum Galaxy was probably first discovered by the Italian astronomer Giovanni Batista Hodierna before 1654.

Hodierna listed the galaxy as a cloud-like nebulosity in his work De systemate orbis cometici; deque admirandis coeli caracteribus (“About the systematics of the cometary orbit, and about the admirable objects of the sky”).

Charles Messier independently discovered the galaxy on the night of August 25-26, 1764 and included it in his catalogue as object number 33.

William Herschel included the object in his own catalogue of nebulae, and also documented the galaxy’s largest and brightest H II region as H III. 150.

The H II region, a diffuse emission nebula that contains ionized hydrogen, was later designated NGC 604.

nebula,triangulum constellation,starburst region
NGC 604 is one of the largest known seething cauldrons of star birth in a nearby galaxy. This monstrous star-birth region contains more than 200 brilliant blue stars within a cloud of glowing gases some 1,300 light-years across, nearly 100 times the size of the Orion Nebula. By contrast, the Orion Nebula contains just four bright central stars. The bright stars in NGC 604 are extremely young by astronomical standards, having formed a mere 3 million years ago. Most of the brightest and hottest stars form a loose cluster located within a cavity near the center of the nebula. Stellar winds from these hot blue stars, along with supernova explosions, are responsible for carving out the hole at the center. The most massive stars in NGC 604 exceed 120 times the mass of our Sun, and their surface temperatures are as hot as 72,000 degrees Fahrenheit. Ultraviolet radiation floods out from these hot stars, making the surrounding nebular gas fluoresce. Image: NASA and The Hubble Heritage Team
It is one of the four brightest H II regions in the Triangulum Galaxy, along with NGC 588, NGC 592 and NGC 595.

NGC 604

NGC 604 is an emission nebula located to the northeast of the central core of the Triangulum Galaxy.

It is about 1,500 light years in diameter, which makes it one of the largest H II regions known and the brightest H II region in the Triangulum Galaxy.

It is also the second most luminous H II region in the Local Group of galaxies.

It is more than 6,300 times more luminous than the more famous Orion Nebula in Orion constellation.

The gas inside the nebula is ionized by a cluster of massive stars at its centre.

The region was discovered by William Herschel on September 11, 1784.

It has an apparent visual magnitude of 14.

NGC 595

NGC 595 is another H II region in the Triangulum Galaxy, about 3 million light years distant from Earth.

It was discovered by the German astronomer Heinrich Ludwig d’Arrest on October 1, 1864.

spiral galaxy
NGC 634 – This spiral galaxy was discovered back in the nineteenth century by French astronomer Édouard Jean-Marie Stephan, but in 2008 it became a prime target for observations thanks to the violent demise of a white dwarf star. The type Ia supernova known as SN2008a was spotted in the galaxy and briefly rivalled the brilliance of its entire host galaxy but, despite the energy of the explosion, it can no longer be seen this Hubble image, which was taken around a year and a half later. Image: ESA, Hubble, NASA
NGC 634

NGC 634 is a spiral galaxy in Triangulum.

It has an apparent visual magnitude of 14 and is approximately 250 million light years distant from Earth.

The galaxy was discovered by the French astronomer Édouard Stephan in the 19th century.

In 2008, a Type Ia supernova, SN 2008a, was observed in the galaxy.

NGC 925

NGC 925 is a barred spiral galaxy in Triangulum.

It has a visual magnitude of 10.7 and is approximately 45 million light years distant from Earth.

interacting galaxies in Triangulum constellation
NGC 672 and IC 1727, image: Wikisky
NGC 672 and IC 1727

NGC 672 and IC 1727 are interacting galaxies in Triangulum.

They are only 88,000 light years distant from each other, and about 18 million light years distant from Earth.

They are located outside the Local Group of galaxies.

NGC 672 is a barred spiral galaxy with an apparent magnitude of 10.7 and IC 1727 has a visual magnitude of 11.4.

NGC 672 was discovered by William Herschel on October 26, 1786, and IC 1727 was discovered by Isaac Roberts on October 29, 1896.

barred spiral galaxy
NGC 784, image: NASA
NGC 784

NGC 784 is another barred spiral galaxy. It lies within the Virgo Supercluster.

The galaxy has an apparent visual magnitude of 12.23 and is approximately 16 million light years distant from the Sun.

NGC 953

NGC 953 is an elliptical galaxy in Triangulum. It has an apparent magnitude of 14.5.

It was discovered by the German astronomer Heinrich Louis d’Arrest on September 26, 1865.