ထရိုင်ဂူလယ် (ကြယ်စုတန်း)

**ထရိုင်ဂူလယ်** သည် မြောက်ဘက်ကောင်းကင်ရှိ သေးငယ်သော ကြယ်စုတန်းတစ်ခု ဖြစ်သည်။ လက်တင်ဘာသာဖြင့်တြိဂံမှ ဆင်းသက်လာခြင်းဖြစ်ပြီး ကြယ်သုံးစင်းထဲတွင် အတောက်ပဆုံးဖြစ်သည်။ ၂ ရာစု တော်လမီ၏ ကြယ်စာရင်းတွင် ၄၈ ခုထဲမှ တစ်ခုအပါဝင်ဖြစ်သော ကြယ်စုတန်းဖြစ်ပြီး ရှေ့ဂရိလူမျိုးများ ဘေဘီလုံလူမျိုးမှားက မှတ်တမ်းတင်ခဲ့သည်။ ကြယ်ဖြူများဖြစ်ကြသော Beta Trianguli နှင့် Gamma Trianguli တို့သည် မြင်သာသောအရွယ်အစား ၃.၀၀၊ ၄.၀၀ အသီးသီးရှိကြသည်။ ထရိုင်ဂူလယ် ကြယ်စုတန်းတွင် ဂလက်ဆီများစွာ တည်ရှိသည်။ အနီးဆုံးနှင့် အတောက်ပဆုံး ဂလက်ဆီမှာ ထရိုင်ဂူလယ် ဂယ်လက်ဆီဖြစ်ပြီး
တနည်းအားဖြင့် Messier 33 ဟုအမည်တွင်ကာ ယင်းသည် Local Group ထဲတွင် အဖွဲ့ဝင်တစ်ခုဖြစ်သည်။ ပထမဆုံး လေ့လာတွေ့ရှိခဲ့သော ကွေဆာ 3C 48 သည်လည်း ထရိုင်ဂူလယ်၏ နယ်နမိတ်တွင် တည်ရှိသည်။

## History and mythology
In the Babylonian star catalogues, Triangulum, together with Gamma Andromedae, formed the constellation known as MULAPIN () "The Plough". It is notable as the first constellation presented on (and giving its name to) a pair of tablets containing canonical star lists that were compiled around 1000&nbsp;BC, the MUL.APIN. The Plough was the first constellation of the "Way of Enlil"—that is, the northernmost quarter of the Sun's path, which corresponds to the 45 days on either side of summer solstice. Its first appearance in the pre-dawn sky (heliacal rising) in February marked the time to begin spring ploughing in Mesopotamia.

The Ancient Greeks called Triangulum *Deltoton* (Δελτωτόν), as the constellation resembled an upper-case Greek letter delta (Δ). It was transliterated by Roman writers, then later Latinised as Deltotum. Eratosthenes linked it with the Nile Delta, while the Roman writer Hyginus associated it with the triangular island of Sicily, formerly known as Trinacria due to its shape. It was also called *Sicilia*, because the Romans believed Ceres, patron goddess of Sicily, begged Jupiter to place the island in the heavens.

Later, the 17th-century German celestial cartographer Johann Bayer called the constellation Triplicitas and Orbis terrarum tripertitus, for the three regions Europe, Asia, and Africa. Triangulus Septentrionalis was a name used to distinguish it from Triangulum Australe, the Southern Triangle. The smaller constellation was not recognised by the International Astronomical Union (IAU) when the constellations were established in the 1920s.

## ဂုဏ်သတ္တိများ
A small constellation, Triangulum is bordered by Andromeda to the north 
and west, Pisces to the west and south, Aries to the south, 
and Perseus to the east. The centre of the constellation lies half way between Gamma 
Andromedae and Alpha Arietis. 
The three-letter abbreviation for the constellation, as adopted by the IAU in 1922, is 'Tri'. 
The official constellation boundaries, as set by Eugène Delporte in 1930, are defined as 
a polygon of 14 segments. In the equatorial coordinate system, the right ascension coordinates of these 
borders lie between  and , while the declination coordinates are between 25.60° 
and 37.35°.  Covering 132 square degrees and 0.320% of the night sky, 
Triangulum ranks 78th of the 88 constellations in size.

## Notable features
Bayer catalogued five stars in the constellation, giving them the Bayer designations Alpha to Epsilon. John Flamsteed added Eta, Iota and four Roman letters; of these, only Iota is still used as the others were dropped in subsequent catalogues and star charts. Flamsteed gave 16 stars Flamsteed designations, of which numbers 1 and 16 are not used—1's coordinates were in error as there was no star present at the location that corresponds to any star in his *Catalogus Britannicus*; Baily presumed that the coordinates were mistranscribed 32s in error by Flamsteed and in fact referred to 7.4 magnitude HD 10407. Baily also noted that 16 Trianguli was closer to Aries and included it in the latter constellation. It is actually a spectroscopic binary system; the primary is a white star of spectral type A5IV with 3.5 times the mass of our sun that is beginning to expand and evolve off the main sequence. The secondary is poorly known, but calculated to be a yellow-white F-type main-sequence star around 1.4 solar masses. The two orbit around a common centre of gravity every 31 days, and are surrounded by a ring of dust that extends from 50 to 400&nbsp;AU away from the stars.

The second-brightest star, the yellow-white subgiant star Alpha Trianguli (3.41m) with a close dimmer companion, is also known as Caput Trianguli or Ras al Muthallath, and is at the apex of the triangle. It lies around 7 degrees north-northwest of Alpha Arietis. Making up the triangle is Gamma Trianguli, a white main sequence star of spectral type A1Vnn of apparent magnitude 4.00 about 112 light-years from Earth. It is around double the size of and around 33 times as luminous as the sun and rotates rapidly. Like Beta, it is surrounded by a dusty debris disk, which has a radius 80 times the distance of the Earth from the Sun. Lying near Gamma and forming an optical triple system with it are Delta and 7 Trianguli. Delta is a spectroscopic binary system composed of two yellow main sequence stars of similar dimensions to the Sun that lies 35 light-years from Earth. The two stars orbit each other every ten days and are a mere 0.1 AU apart. This system is the closest in the constellation to the Earth.

Iota Trianguli is a double star whose components can be separated by medium-sized telescopes into a strong yellow and a contrasting pale blue star. Both of these are themselves close binaries. X Trianguli is an eclipsing binary system that ranges between magnitudes 8.5 and 11.2 over a period of 0.97 days. RW Trianguli is a cataclysmic variable star system composed of a white dwarf primary and an orange main sequence star of spectral type K7 V. The former is drawing off matter from the latter, forming a prominent accretion disc. The system is around 1075 light-years distant.

R Trianguli is a long period (Mira) variable that ranges from magnitude 6.2 to 11.7 over a period of 267 days. HD 12545, also known as XX Trianguli, is
an orange giant of spectral type K0III around 520 light-years distant with a visual magnitude of 8.42. A huge starspot larger than the diameter of the sun was detected on its surface in 1999 by astronomers using Doppler imaging.

Three star systems appear to have planets. HD 9446 is a sun-like star around 171 light-years distant that has two planets of masses 0.7 and 1.8 times that of Jupiter, with orbital periods of 30 and 193 days respectively. WASP-56 is a sun-like star of spectral type G6 and apparent magnitude 11.48 with a planet 0.6 the mass of Jupiter that has a period of 4.6 days. HD 13189 is an orange giant of spectral type K2II about 2–7 times as massive as the sun with a planetary or brown dwarf companion between 8 and 20 times as massive as Jupiter, which takes 472 days to complete an orbit. It is one of the largest stars discovered to have a planetary companion.

### Deep-sky objects
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The Triangulum Galaxy, also known as Messier 33, was discovered by Giovanni Battista Hodierna in the 17th century. A distant member of the Local Group, it is about 2.3 million light-years away, and at magnitude 5.8 it is bright enough to be seen by the naked eye under the darkest skies. Under light-polluted skies, it is challenging or invisible even in a small telescope or binoculars. Because of its low surface brightness, low power is required. It is a spiral galaxy with a diameter of 46,000 light-years and is thus smaller than both the Andromeda Galaxy and the Milky Way. A distance of less than 300 kiloparsecs between it and Andromeda supports the hypothesis that it is a satellite of the larger galaxy. Within the constellation, it lies near the border of Pisces, 3.5 degrees west-northwest of Alpha Trianguli and 7 degrees southwest of Beta Andromedae.

In addition to M33, there are several NGC galaxies of visual magnitudes 12 to 14. These two plus another four nearby dwarf irregular galaxies constitute the NGC 672 group, and all six appear to have had a burst of star formation in the last ten million years. The group is thought connected to another group of six galaxies known as the NGC 784 group, named for its principal galaxy, the barred spiral NGC 784. Together with two isolated dwarf galaxies, these fourteen appear to be moving in a common direction and constitute a group possibly located on a dark matter filament. 3C 48 was the first quasar ever to be observed, although its true identity was not uncovered until after that of 3C 273 in 1963. It has an apparent magnitude of 16.2 and is located about 5 degrees northwest of Alpha Trianguli.

## ကိုးကား
## ပြင်ပလင့် 
* Warburg Institute Iconographic Database (over 140 medieval and early modern images of the Triangulum) 

ကဏ္ဍ:ကြယ်စုတန်းများ