Triangulum is a small constellation in the northern sky. Its name is Latin for ‘triangle,’ derived from its three brightest stars, which form a long and narrow triangle. Known to the ancient Babylonians and Greeks, Triangulum was one of the 48 constellations listed by the 2nd century astronomer Ptolemy. The celestial cartographers Johann Bayer and John Flamsteed catalogued the constellation’s stars, giving six of them Bayer designations.
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. In the equatorial coordinate system, the right ascension coordinates of the constellation lie between 01h 31.3m and 02h 50.4m, 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.
Triangulum constellation, John Flamsteed, Atlas Coelestis, London: 1729
[http://starrytransit.mmoca.org/showFullImage.php?image=glowacki_33_full.jpg&caption=Triangulum%20constellation%2C%20John%20Flamsteed%2C%20%3Ci%3EAtlas%20Coelestis%3C/i%3E%2C%20London:%201729.&alt=Constellation,%20John%20Flamsteed]
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 BCE, 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. Greek astronomers such as Hipparchos and Ptolemy called it Trigonon (Τρίγωνον), and later, it was Romanized as Trigonum. Other names referring to its shape include Tricuspis and Triquetrum.
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. Polish astronomer Johannes Hevelius excised three faint stars- 6, 10 and 12 Trianguli- to form the new constellation of Triangulum Minus, renaming the original as Triangulum Majus, but is no longer in use.
In Chinese astronomy, Gamma Andromedae and neighbouring stars including Beta, Gamma and Delta Trianguli were called Teen Ta Tseang Keun (‘Heaven’s great general’), representing honour in astrology and a great general in mythology.
[http://astropixels.com/constellations/charts/Tri.html]
[http://astrojunkie.friendhood.net/t139-constellation-guide-triangulum]
Three stars (alpha, beta and gamma Trianguli) make up the long narrow triangle that gives the constellation its name. The brightest member is the white giant star Beta Trianguli of apparent magnitude 3.00, lying 127 light-years distant from Earth. 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 AU away from the stars.
The second-brightest star, the yellow-white subgiant star Alpha Trianguli 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.
Delta Trianguli is a spectroscopic binary star system approximately 35 light-years (11 pc) away. The primary star is a yellow dwarf, while the secondary star is thought to be an orange dwarf. It has an apparent magnitude of +4.87 and forms an optical (line-of-sight) triple with Gamma Trianguli.
[https://en.wikipedia.org/wiki/Delta_Trianguli]
XX Trianguli (HD 12545) is a variable star in the constellation Triangulum. It is classified as a RS Canum Venaticorum variable orange giant with spectral type K0III, and it is notable for having a huge starspot larger than the diameter of the Sun, discovered using Doppler imaging:
[https://apod.nasa.gov/apod/ap031102.html]
A Giant Starspot on HD 12545
What could cause a star to have such a large spot? Our Sun itself frequently has sunspots, relatively cool dark magnetic depressions that move across its surface. HD 12545, however, exhibits the largest starspots yet observed. Doppler imaging- the use of slight changes in color caused by the rotation of the star- was used to create this false-color image. The vertical bar on the right gives a temperature scale in kelvins. This giant, binary, RS CVn star, also known as XX Trianguli, is visible with binoculars in the constellation of Triangulum. The starspot is thought to be caused by large magnetic fields that inhibit hot matter from flowing to the surface.
[https://apod.nasa.gov/apod/ap031102.html]
The constellation contains several galaxies, the brightest and nearest of which is the Triangulum Galaxy or Messier 33- a member of the Local Group. The galaxy was discovered by Giovanni Battista Hodierna in the 17th century. 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:
M33: Triangulum Galaxy
The small, northern constellation Triangulum harbors this magnificent face-on spiral galaxy, M33. Its popular names include the Pinwheel Galaxy or just the Triangulum Galaxy. M33 is over 50,000 light-years in diameter, third largest in the Local Group of galaxies after the Andromeda Galaxy (M31), and our own Milky Way. About 3 million light-years from the Milky Way, M33 is itself thought to be a satellite of the Andromeda Galaxy and astronomers in these two galaxies would likely have spectacular views of each other’s grand spiral star systems. As for the view from planet Earth, this sharp composite image, a 25 panel mosaic, nicely shows off M33’s blue star clusters and pinkish star forming regions that trace the galaxy’s loosely wound spiral arms. In fact, the cavernous NGC 604 is the brightest star forming region, seen here at about the 1 o'clock position from the galaxy center. Like M31, M33’s population of well-measured variable stars have helped make this nearby spiral a cosmic yardstick for establishing the distance scale of the Universe.
[http://apod.nasa.gov/apod/ap121220.html]
Within M33, NGC 604 is an H II region where star formation takes place:
NGC 604: Giant Stellar Nursery
Stars are sometimes born in the midst of chaos. About 3 million years ago in the nearby galaxy M33, a large cloud of gas spawned dense internal knots which gravitationally collapsed to form stars. NGC 604 was so large, however, it could form enough stars to make a globular cluster. Many young stars from this cloud are visible in the above image from the Hubble Space Telescope, along with what is left of the initial gas cloud. Some stars were so massive they have already evolved and exploded in a supernova. The brightest stars that are left emit light so energetic that they create one of the largest clouds of ionized hydrogen gas known, comparable to the Tarantula Nebula in our Milky Way’s close neighbor, the Large Magellanic Cloud.
[http://apod.nasa.gov/apod/ap121211.html]
NGC 634 is a spiral galaxy in Triangulum. It has an apparent 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:
[http://www.constellation-guide.com/constellation-list/triangulum-constellation/]
A perfect spiral with an explosive secret
The NASA/ESA Hubble Space Telescope is renowned for its breathtaking images and this snapshot of NGC 634 is definitely that- the fine detail and exceptionally perfect spiral structure of the galaxy make it hard to believe that this is a real observation and not an artist’s impression or a screenshot taken straight from Star Wars.
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.
White dwarfs are thought to be the endpoint of evolution for stars between 0.07 to 8 solar masses, which equates to 97% of the stars in the Milky Way. However, there are exceptions to the rule; in a binary system it is possible for a white dwarf to accrete material from the companion star and gradually put on weight. Like a person gorging on junk food, the star can eventually grow too full- when it exceeds 1.38 solar masses nuclear reactions ignite that produce enormous amounts of energy and the star explodes as a type Ia supernova.
This picture was created from images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through a yellow filter (F555W, colored blue) have been combined with images through red (F625W, colored green) and near-infrared (F775W, colored red) filters. The total exposure times per filter were 3750 s, 3530 s and 2484 s, respectively and the field of view is 2.5 x 1.5 arcminutes.
[https://www.spacetelescope.org/images/potw1122a/]
3C 48
[https://en.wikipedia.org/wiki/3C_48]
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.
[https://en.wikipedia.org/wiki/Triangulum]
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