Utente:Paperoastro/Sandbox3
La Galassia del Triangolo, conosciuta anche con il nome di M33 (oggetto numero 33 del catalogo di Charles Messier) e di NGC 598, è una galassia a spirale di tipo Sc distante circa 3 milioni di anno luce dalla Terra e situata nella costellazione del Triangolo. Nel mondo anglosassone questa galassia è anche informalmente chiamata Pinwheel Galaxy (in italiano letteralmente Galassia Girandola) in alcune pubblicazioni amatoriali di astronomia[1], ma anche in alcuni comunicati ufficiali di siti professionali[2]. Tuttavia sia il database professionale SIMBAD Astronomical Database, che contiene i nomi e le designazioni formali di vari oggetti astronomici, che diversi altri siti per l'astronomia amatoriale indicano con il nome di "Pinwheel Galaxy" la galassia M101[3][4].
Osservazione
General information
The Triangulum Galaxy can be seen with the naked eye, if the level of light pollution is sufficiently low[5]. Being a diffuse object, its visibility is strongly affected by even small amounts of light pollution, ranging from easily visible in direct vision in truly dark skies to a difficult averted vision object in rural/suburban skies[5]. The fainter and more distant galaxies Messier 81 and Centaurus A have also been seen with the naked eye by very experienced observers[6]. However, some amateur astronomers may confuse the object with the nearby NGC 752, an open cluster that is brighter than the Triangulum Galaxy. [senza fonte] No known pre-telescopic observer notes it, which is not surprising: given its indistinctness, it is not likely to be noticed as an object unless one already knows of its existence.
The Triangulum Galaxy was probably discovered by Giovanni Batista Hodierna before 1654, who may have grouped it together with open cluster, NGC 752. It was independently discovered by Charles Messier in 1764, who catalogued it as M33 on August 25. M33 was also catalogued independently by William Herschel on September 11, 1784 number H V.17. It was among the first "spiral nebulae" identified as such by Lord Rosse.
Herschel also cataloged The Triangulum Galaxy's brightest and largest H II region (diffuse emission nebula containing ionized hydrogen) as H III.150 separately from the galaxy itself, which eventually obtained NGC number 604. As seen from Earth NGC 604 is located northeast of the galaxy's central core, and is one of the largest H II regions known with a diameter of nearly 1500 light-years and a spectrum similar to the Orion Nebula. Herschel also noted 3 other smaller H II regions (NGC 588, 592 and 595).
In 2005, using observations of two water masers on opposite sides of Triangulum via the VLBA, researchers were, for the first time, able to estimate the angular rotation and proper motion of Triangulum. A velocity of 190 ± 60 km/s relative to the Milky Way is computed which means Triangulum is moving towards Andromeda.[7]
In 2007, a black hole about 15.7 times the mass of the Sun was detected in the galaxy using data from the Chandra X-ray Observatory. The black hole, named M33 X-7, orbits a companion star which it eclipses every 3.5 days.[8]
The galaxy has an H II nucleus.[9]
- ^ (EN) S. J. O'Meara, The Messier Objects, Cambridge, Cambridge University, 1998, ISBN 0-521-55332-6.
- ^ (EN) NASA Spitzer Telescope Reveals Pinwheel Galaxy's Hidden Wonders, su spaceref.com. URL consultato il 24-11-2009.
- ^ SIMBAD Astronomical Database: risultato per (EN) M101, su simbad.u-strasbg.fr. URL consultato il 24-11-2009.
- ^ (EN) Messier Object 101, su seds.org. URL consultato il 24-11-2009.
- ^ a b http://www.skyandtelescope.com/resources/darksky/3304011.html
- ^ [1]; [2]
- ^ Brunthaler, Andreas; Reid, Mark J.; Falcke, Heino; Greenhill, Lincoln J.; Henkel, Christian, The Geometric Distance and Proper Motion of the Triangulum Galaxy (M33), in Science, vol. 307, n. 5714, 2005, pp. 1440–1443, DOI:10.1126/science.1108342.
- ^ Morcone, Jennifer, Heaviest Stellar Black Hole Discovered in Nearby Galaxy, Chandra X-ray Observatory press release, ottobre 17, 2007
- ^ Ho, Luis C., A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies, in The Astrophysical Journal Supplement Series, vol. 112, October 1997, pp. 315–390, DOI:10.1086/313041.