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< Messier Index

Contents

Introduction





The Index of Astronomy Objects

Volume 1

Messier Index

Stellar spire eagle nebula.jpg The Crab Nebula
Messier 17





Table of Contents

Introduction

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List of Messier Objects

     Star cluster      Nebula      Galaxy      Other

Messier number NGC Number Common name Picture Object type Distance (kly) Constellation Apparent magnitude
M1[1] NGC 1952 Crab Nebula Crab Nebula.jpg Supernova remnant 6.3 Taurus 9.0
M2[2] NGC 7089   Messier 2 Hubble WikiSky.jpg Globular cluster 36 Aquarius 7.5
M3[3] NGC 5272   M3LRGB 891x674.jpg Globular cluster 31 Canes Venatici 7.0
M4[4] NGC 6121   Messier 4 Hubble WikiSky.jpg Globular cluster 7 Scorpius 7.5
M5[5] NGC 5904   Messier 5 Hubble WikiSky.jpg Globular cluster 23 Serpens 7.0
M6[6] NGC 6405 Butterfly Cluster M6a.jpg Open cluster 2 Scorpius 4.5
M7[7] NGC 6475 Ptolemy Cluster Open-cluster-Messier-7.jpeg Open cluster 1 Scorpius 3.5
M8[8] NGC 6523 Lagoon Nebula LagoonHunterWilson.jpg Cluster with nebula 6.5 Sagittarius 5.0
M9[9] NGC 6333   Messier object 009.jpg Globular cluster 26 Ophiuchus 9.0
M10[10] NGC 6254   Messier 10 Hubble WikiSky.jpg Globular cluster 13 Ophiuchus 7.5
M11[11] NGC 6705 Wild Duck Cluster Messier11.jpg Open cluster 6 Scutum 7.0
M12[12] NGC 6218   M12 Hubble.jpg Globular cluster 18 Ophiuchus 8.0
M13[13] NGC 6205 Great Globular Cluster in Hercules Messier 13 Hubble WikiSky.jpg Globular cluster 22 Hercules 5.8
M14[14] NGC 6402   Messier object 014.jpg Globular cluster 27 Ophiuchus 9.5
M15[15] NGC 7078 Cúmulo de Pegaso Messier 15 Hubble WikiSky.jpg Globular cluster 33 Pegasus 7.5
M16[16] NGC 6611 Eagle Nebula Stellar spire eagle nebula.jpg Cluster with H II region 7 Serpens 6.5
M17[17] NGC 6618 Omega Nebula Messier 17.jpg Cluster with H II region 5 Sagittarius 7.0
M18[18] NGC 6613   Messier18.jpg Open cluster 6 Sagittarius 8.0
M19[19] NGC 6273   Messier object 019.jpg Globular cluster 27 Ophiuchus 8.5
M20[20] NGC 6514 Trifid Nebula Trifid.nebula.arp.750pix.jpg Cluster with H II region 2.2 Sagittarius 5.0
M21[21] NGC 6531   Messier object 021.jpg Open cluster 3 Sagittarius 7.0
M22[22] NGC 6656 Sagittarius Cluster Messier object 022.jpg Globular cluster 10 Sagittarius 6.5
M23[23] NGC 6494   Messier object 023.jpg Open cluster 4.5 Sagittarius 6.0
M24[24] NGC 6603 Sagittarius Star Cloud Messier object 024.jpg Milky Way star cloud 10 Sagittarius 11.5
M25[25] IC 4725   Messier object 025.jpg Open cluster 2 Sagittarius 4.9
M26[26] NGC 6694   Messier object 026.jpg Open cluster 5 Scutum 9.5
M27[27] NGC 6853 Dumbbell Nebula Messier27.jpg Planetary nebula 1.25 Vulpecula 7.5
M28[28] NGC 6626   Messier28.jpg Globular cluster 18 Sagittarius 8.5
M29[29] NGC 6913   Messier object 029.jpg Open cluster 7.2 Cygnus 9.0
M30[30] NGC 7099   Messier object 030.jpg Globular cluster 25 Capricornus 8.5
M31[31] NGC 224 Andromeda Galaxy Andromeda galaxy.jpg Spiral galaxy 2,500 Andromeda 3.5
M32[32] NGC 221   M32.jpg Dwarf elliptical galaxy 2,900 Andromeda 10.0
M33[33] NGC 598 Triangulum Galaxy PIA03033.jpg Spiral galaxy 2,590 Triangulum 7.0
M34[34] NGC 1039   M34 2mass atlas.jpg Open cluster 1.4 Perseus 6.0
M35[35] NGC 2168   M35atlas.jpg Open cluster 2.8 Gemini 5.5
M36[36] NGC 1960   M29a.jpg Open cluster 4.1 Auriga 6.5
M37[37] NGC 2099   M37a.jpg Open cluster 4.6 Auriga 6.0
M38[38] NGC 1912   Messier object 038.jpg Open cluster 4.2 Auriga 7.0
M39[39] NGC 7092   Messier object 039.jpg Open cluster 0.8 Cygnus 5.5
M40[40]   Winnecke 4 Messier object 40.jpg Double star]WNC4   Ursa Major 9.0
M41[41] NGC 2287   M41atlas.jpg Open cluster 2.4 Canis Major 5.0
M42[42] NGC 1976 Orion Nebula Orion Nebula - Hubble 2006 mosaic 18000.jpg H II region 1.6 Orion 5.0
M43[43] NGC 1982 De Mairan's Nebula Messier object 043.jpg H II region
(part of the Orion Nebula)
1.6 Orion 7.0
M44[44] NGC 2632 Beehive Cluster Messier object 044.jpg Open cluster 0.5 Cancer 4.0
M45[45]   Pleiades Open cluster 0.4 Taurus 1.4
M46[46] NGC 2437   M46a.jpg Open cluster 5.4 Puppis 6.5
M47[47] NGC 2422   M47a.jpg Open cluster 1.6 Puppis 4.5
M48[48] NGC 2548   M48a.jpg Open cluster 1.5 Hydra 5.5
M49[49] NGC 4472   M49a.jpg Elliptical galaxy 60,000 Virgo 10.0
M50[50] NGC 2323   M50a.jpg Open cluster 3 Monoceros 7.0
M51[51] NGC 5194, NGC 5195 Whirlpool Galaxy Whirlpool (M51).jpg Spiral galaxy 37,000 Canes Venatici 8.0
M52[52] NGC 7654   M52atlas.jpg Open cluster 7 Cassiopeia 8.0
M53[53] NGC 5024   Globular Cluster M53.jpg Globular cluster 56 Coma Berenices 8.5
M54[54] NGC 6715   Messier54.jpg Globular cluster 83 Sagittarius 8.5
M55[55] NGC 6809   Messier55.jpg Globular cluster 17 Sagittarius 7.0
M56[56] NGC 6779   M56-LRGB.jpg Globular cluster 32 Lyra 9.5
M57[57] NGC 6720 Ring Nebula Ring Nebula.jpg Planetary nebula 2.3 Lyra 9.5
M58[58] NGC 4579   M58s.jpg Barred spiral galaxy 60,000 Virgo 11.0
M59[59] NGC 4621   Elliptical galaxy 60,000 Virgo 11.5
M60[60] NGC 4649   Messier object 060.jpg Elliptical galaxy 60,000 Virgo 10.5
M61[61] NGC 4303   M61.jpg Spiral galaxy 60,000 Virgo 10.5
M62[62] NGC 6266   Messier object 062.jpg Globular cluster 22 Ophiuchus 8.0
M63[63] NGC 5055 Sunflower Galaxy M63.jpg Spiral galaxy 37,000 Canes Venatici 8.5
M64[64] NGC 4826 Black Eye Galaxy Blackeyegalaxy.jpg Spiral galaxy 12,000 Coma Berenices 9.0
M65[65] NGC 3623   M65.jpg Barred spiral galaxy 35,000 Leo 10.5
M66[66] NGC 3627   Sig05-016.jpg Barred spiral galaxy 35,000 Leo 10.0
M67[67] NGC 2682   Messier object 067.jpg Open cluster 2.25 Cancer 7.5
M68[68] NGC 4590   Messier object 068.jpg Globular cluster 32 Hydra 9.0
M69[69] NGC 6637   Messier object 069.jpg Globular cluster 25 Sagittarius 9.0
M70[70] NGC 6681   Messier70.jpg Globular cluster 28 Sagittarius 9.0
M71[71] NGC 6838   Messier71.jpg Globular cluster 12 Sagitta 8.5
M72[72] NGC 6981   Messier72.jpg Globular cluster 53 Aquarius 10.0
M73[73] NGC 6994   Messier73.jpg Asterism   Aquarius 9.0
M74[74] NGC 628   NGC 628.jpg Spiral galaxy 35,000 Pisces 10.5
M75[75] NGC 6864   Messier75.jpg Globular cluster 58 Sagittarius 9.5
M76[76] NGC 650, NGC 651 Little Dumbbell Nebula M76-RL5-DDmin-Gamma-LRGB 883x628.jpg Planetary nebula 3.4 Perseus 12.0
M77[77] NGC 1068   Spiral Galaxy M77.jpg Spiral galaxy 60,000 Cetus 10.5
M78[78] NGC 2068   M78 sdss.jpg Diffuse nebula 1.6 Orion 8.0
M79[79] NGC 1904   M79a.jpg Globular cluster 40 Lepus 8.5
M80[80] NGC 6093   A Swarm of Ancient Stars - GPN-2000-000930.jpg Globular cluster 27 Scorpius 8.5
M81[81] NGC 3031 Bode's Galaxy NGC 3031SSTsig07-009 medium.jpg Spiral galaxy 11,000 Ursa Major 8.5
M82[82] NGC 3034 Cigar Galaxy Messier82.jpg Barred spiral galaxy (?) 11,000 Ursa Major 9.5
M83[83] NGC 5236 Southern Pinwheel Galaxy M83g.jpg Barred spiral galaxy 10,000 Hydra 8.5
M84[84] NGC 4374   Messier84a.jpg Lenticular galaxy 60,000 Virgo 11.0
M85[85] NGC 4382   Messier 85 Hubble WikiSky.jpg Lenticular galaxy 60,000 Coma Berenices 10.5
M86[86] NGC 4406   Messier 86 Hubble WikiSky.jpg Lenticular galaxy 60,000 Virgo 11.0
M87[87] NGC 4486   M87 jet.jpg Elliptical galaxy 60,000 Virgo 11.0
M88[88] NGC 4501   Messier object 088.jpg Spiral galaxy 60,000 Coma Berenices 11.0
M89[89] NGC 4552   Elliptical galaxy 60,000 Virgo 11.5
M90[90] NGC 4569   Messier object 090.jpg Spiral galaxy 60,000 Virgo 11.0
M91[91] NGC 4548   Messier91.jpg Spiral galaxy 60,000 Coma Berenices 11.5
M92[92] NGC 6341   Globular Cluster M92.JPG Globular cluster 26 Hercules 7.5
M93[93] NGC 2447   Messier object 093.jpg Open cluster 4.5 Puppis 6.5
M94[94] NGC 4736   Messier object 094.jpg Spiral galaxy 14,500 Canes Venatici 9.5
M95[95] NGC 3351   Messier95 spitzer.jpg Spiral galaxy 38,000 Leo 11.0
M96[96] NGC 3368   Messier object 096.jpg Spiral galaxy 38,000 Leo 10.5
M97[97] NGC 3587 Owl Nebula M97 FTN.jpg Planetary nebula 2.6 Ursa Major 12.0
M98[98] NGC 4192   M-98.jpg Spiral galaxy 60,000 Coma Berenices 11.0
M99[99] NGC 4254   M99.jpg Spiral galaxy 60,000 Coma Berenices 10.5
M100[100] NGC 4321   Spiral Galaxy M100.jpg Spiral galaxy 60,000 Coma Berenices 10.5
M101[101] NGC 5457 Pinwheel Galaxy M101 hires STScI-PRC2006-10a.jpg Spiral galaxy 24,000 Ursa Major 8.5
M102[102] (Not conclusively identified)[103]          
M103[104] NGC 581   Messier object 103.jpg Open cluster 8 Cassiopeia 7.0
M104[105] NGC 4594 Sombrero Galaxy M104 ngc4594 sombrero galaxy hi-res.jpg Spiral galaxy 50,000 Virgo 9.5
M105[106] NGC 3379   Messier object 105.jpg Elliptical galaxy 38,000 Leo 11.0
M106[107] NGC 4258   Messier 106 by Spitzer.jpg Spiral galaxy 25,000 Canes Venatici 9.5
M107[108] NGC 6171   Messier object 107.jpg Globular cluster 20 Ophiuchus 10.0
M108[109] NGC 3556   M108a.gif Spiral galaxy 45,000 Ursa Major 11.0
M109[110] NGC 3992   Messier object 109.jpg Spiral galaxy 55,000 Ursa Major 11.0
M110[111] NGC 205   M110 Lanoue.png Dwarf elliptical galaxy 2,200 Andromeda 10.0
Messier number NGC Number Common name Picture Object type Distance (kly) Constellation Apparent magnitude

Star Chart

Messier Star Chart


Messier 1

Crab Nebula
Crab Nebula.jpg
M1, the Crab Nebula. Courtesy of NASA/ESA
Observation data: J2000.0 epoch
Type Supernova Remnant
Right ascension 05h 34m 31.97s[112]
Declination +22° 00′ 52.1″[112]
Distance 6.5 ± 1.6 kly (2.0 ± 0.5 kpc)[113]
Apparent magnitude (V) +8.4
Apparent dimensions (V) 420″ × 290″[114][a]
Constellation Taurus
Physical characteristics
Radius 5.5 ly (1.7 pc) [115]
Absolute magnitude (V) -3.1 ± 0.5[b]
Notable features Optical pulsar
Other designations M1,[112] NGC 1952[112], Sharpless 244

The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant and pulsar wind nebula in the constellation of Taurus. The nebula was first observed by John Bevis in 1731, and corresponds to a bright supernova recorded by Chinese and Arab astronomers in 1054. At X-ray and gamma-ray energies above 30 KeV, the Crab is generally the strongest persistent source in the sky, with measured flux extending to above 1012 eV. Located at a distance of about 6,500 light-years (2 kpc) from Earth, the nebula has a diameter of 11 ly (3.4 pc) and expands at a rate of about 1,500 kilometers per second.

At the center of the nebula lies the Crab Pulsar, a rotating neutron star, which emits pulses of radiation from gamma-rays to radio waves with a spin rate of 30.2 times per second. The nebula was the first astronomical object identified with a historical supernova explosion.

The nebula acts as a source of radiation for studying celestial bodies that occult it. In the 1950s and 1960s, the Sun's corona was mapped from observations of the Crab's radio waves passing through it, and more recently, the thickness of the atmosphere of Saturn's moon Titan was measured as it blocked out X-rays from the nebula.

Origins

First observed in 1731 by John Bevis, the Crab Nebula corresponds to the bright SN 1054 supernova that was recorded by Chinese and Arab astronomers in 1054. The nebula was independently rediscovered in 1758 by Charles Messier as he was observing a bright comet. Messier catalogued it as the first entry in his catalogue of comet-like objects. The Earl of Rosse observed the nebula at Birr Castle in the 1840s, and referred to the object as the Crab Nebula because a drawing he made of it looked like a crab.[116]

In the early 20th century, the analysis of early photographs of the nebula taken several years apart revealed that it was expanding. Tracing the expansion back revealed that the nebula must have become visible on Earth about 900 years ago. Historical records revealed that a new star bright enough to be seen in the daytime had been recorded in the same part of the sky by Chinese and Arab astronomers in 1054[117][118] Given its great distance, the daytime "guest star" observed by the Chinese and Arabs could only have been a supernova—a massive, exploding star, having exhausted its supply of energy from nuclear fusion and collapsed in on itself.

Recent analysis of historical records have found that the supernova that created the Crab Nebula probably appeared in April or early May, rising to its maximum brightness of between apparent magnitude −7 and −4.5 (brighter than everything in the night sky except the Moon) by July. The supernova was visible to the naked eye for about two years after its first observation.[119] Thanks to the recorded observations of Far Eastern and Middle Eastern astronomers of 1054, Crab Nebula became the first astronomical object recognized as being connected to a supernova explosion.[118]

Physical conditions

The Crab Nebula seen in infrared by the Spitzer Space Telescope.
Hubble Space Telescope image of a small region of the Crab Nebula, showing Rayleigh–Taylor instabilities in its intricate filamentary structure. Credit: NASA/ESA.

In visible light, the Crab Nebula consists of a broadly oval-shaped mass of filaments, about 6 arcminutes long and 4 arcminutes wide (by comparison, the full moon is 30 arcminutes across) surrounding a diffuse blue central region. In three dimensions, the nebula is thought to be shaped like a prolate spheroid.[114] The filaments are the remnants of the progenitor star's atmosphere, and consist largely of ionised helium and hydrogen, along with carbon, oxygen, nitrogen, iron, neon and sulfur. The filaments' temperatures are typically between 11,000 and 18,000 K, and their densities are about 1,300 particles per cm³.[120]

In 1953 Iosif Shklovsky proposed that the diffuse blue region is predominantly produced by synchrotron radiation, which is radiation given off by the curving of electrons moving at speeds up to half the speed of light.[121] Three years later the theory was confirmed by observations. In the 1960s it was found that the source of the electron curved paths was the strong magnetic field produced by a neutron star at the center of the nebula.[122]

Distance

Even though the Crab Nebula is the focus of much attention among astronomers, its distance remains an open question due to uncertainties in every method used to estimate its distance. In 2008, the general consensus is that its distance from Earth is 2.0 ± 0.5 kpc (6.5 ± 1.6 kly). The Crab Nebula is currently expanding outwards at about 1,500 km/s.[123] Images taken several years apart reveal the slow expansion of the nebula[124], and by comparing this angular expansion with its spectroscopically determined expansion velocity, the nebula's distance can be estimated. In 1973, an analysis of many different methods used to compute the distance to the nebula reached a conclusion of about 6,300 ly.[114] Along its longest visible dimension, it measures about 13 ± 3 ly across.[c]

Tracing back its expansion consistently yields a date for the creation of the nebula several decades after 1054, implying that its outward velocity has accelerated since the supernova explosion.[125] This acceleration is believed to be caused by energy from the pulsar that feeds into the nebula's magnetic field, which expands and forces the nebula's filaments outwards.[126]

Mass

Estimates of the total mass of the nebula are important for estimating the mass of the supernova's progenitor star. The amount of matter contained in the Crab Nebula's filaments (ejecta mass of ionized and neutral gas; mostly helium[127]) is estimated to be 4.6 ± 1.8 M?.[128]

Helium-rich torus

One of the many nebular components (or anomalies) of the Crab is a helium-rich torus which is visible as an east-west band crossing the pulsar region. The torus composes about 25% of the visible ejecta and is composed of about 95% helium. As of yet, there has been no plausible explanation put forth for the structure of the torus.[129]

Central star

The Crab Pulsar. This image combines optical data from Hubble (in red) and X-ray images from Chandra X-ray Observatory (in blue).

At the centre of the Crab Nebula are two faint stars, one of which is the star responsible for the existence of the nebula. It was identified as such in 1942, when Rudolf Minkowski found that its optical spectrum was extremely unusual.[130] The region around the star was found to be a strong source of radio waves in 1949[131] and X-rays in 1963,[132] and was identified as one of the brightest objects in the sky in gamma rays in 1967.[133] Then, in 1968, the star was found to be emitting its radiation in rapid pulses, becoming one of the first pulsars to be discovered.

Pulsars are sources of powerful electromagnetic radiation, emitted in short and extremely regular pulses many times a second. They were a great mystery when discovered in 1967, and the team which identified the first one considered the possibility that it could be a signal from an advanced civilization.[134] However, the discovery of a pulsating radio source in the centre of the Crab Nebula was strong evidence that pulsars were formed by supernova explosions. They are now understood to be rapidly rotating neutron stars, whose powerful magnetic field concentrates their radiation emissions into narrow beams.

The Crab Pulsar is believed to be about 28–30 km in diameter;[135] it emits pulses of radiation every 33 milliseconds.[136] Pulses are emitted at wavelengths across the electromagnetic spectrum, from radio waves to X-rays. Like all isolated pulsars, its period is slowing very gradually. Occasionally, its rotational period shows sharp changes, known as 'glitches', which are believed to be caused by a sudden realignment inside the neutron star. The energy released as the pulsar slows down is enormous, and it powers the emission of the synchrotron radiation of the Crab Nebula, which has a total luminosity about 75,000 times greater than that of the Sun.[137]

The pulsar's extreme energy output creates an unusually dynamic region at the centre of the Crab Nebula. While most astronomical objects evolve so slowly that changes are visible only over timescales of many years, the inner parts of the Crab show changes over timescales of only a few days.[138] The most dynamic feature in the inner part of the nebula is the point where the pulsar's equatorial wind slams into the bulk of the nebula, forming a shock front. The shape and position of this feature shifts rapidly, with the equatorial wind appearing as a series of wisp-like features that steepen, brighten, then fade as they move away from the pulsar to well out into the main body of the nebula.

Progenitor star

This sequence of Hubble Space Telescope images shows features in the inner Crab Nebula changing over a period of four months. Credit: NASA/ESA.

The star that exploded as a supernova is referred to as the supernova's progenitor star. Two types of stars explode as supernovae: white dwarfs and massive stars. In the so-called Type Ia supernovae, gases falling onto a white dwarf raise its mass until it nears a critical level, the Chandrasekhar limit, resulting in an explosion; in Type Ib/c and Type II supernovae, the progenitor star is a massive star which runs out of fuel to power its nuclear fusion reactions and collapses in on itself, reaching such phenomenal temperatures that it explodes. The presence of a pulsar in the Crab means that it must have formed in a core-collapse supernova; Type Ia supernovae do not produce pulsars.

Theoretical models of supernova explosions suggest that the star that exploded to produce the Crab Nebula must have had a mass of between 9 and 11 M?.[129][139] Stars with masses lower than 8 solar masses are thought to be too small to produce supernova explosions, and end their lives by producing a planetary nebula instead, while a star heavier than 12 solar masses would have produced a nebula with a different chemical composition to that observed in the Crab.[140]

A significant problem in studies of the Crab Nebula is that the combined mass of the nebula and the pulsar add up to considerably less than the predicted mass of the progenitor star, and the question of where the 'missing mass' is remains unresolved.[128] Estimates of the mass of the nebula are made by measuring the total amount of light emitted, and calculating the mass required, given the measured temperature and density of the nebula. Estimates range from about 1–5 solar masses, with 2–3 solar masses being the generally accepted value.[140] The neutron star mass is estimated to be between 1.4 and 2 solar masses.

The predominant theory to account for the missing mass of the Crab is that a substantial proportion of the mass of the progenitor was carried away before the supernova explosion in a fast stellar wind. However, this would have created a shell around the nebula. Although attempts have been made at several different wavelengths to observe a shell, none has yet been found.[141]

Transits by solar system bodies

The Crab Nebula lies roughly 1½ ° away from the ecliptic—the plane of Earth's orbit around the Sun. This means that the Moon—and occasionally, planets—can transit or occult the nebula. Although the Sun does not transit the nebula, its corona passes in front of it. These transits and occultations can be used to analyse both the nebula and the object passing in front of it, by observing how radiation from the nebula is altered by the transiting body.

Lunar transits have been used to map X-ray emissions from the nebula. Before the launch of X-ray-observing satellites, such as the Chandra X-ray Observatory, X-ray observations generally had quite low angular resolution, but when the Moon passes in front of the nebula, its position is very accurately known, and so the variations in the nebula's brightness can be used to create maps of X-ray emission.[142] When X-rays were first observed from the Crab, a lunar occultation was used to determine the exact location of their source.[132]

The Sun's corona passes in front of the Crab every June. Variations in the radio waves received from the Crab at this time can be used to infer details about the corona's density and structure. Early observations established that the corona extended out to much greater distances than had previously been thought; later observations found that the corona contained substantial density variations.[143]

Very rarely, Saturn transits the Crab Nebula. Its transit in 2003 was the first since 1296; another will not occur until 2267. Observers used the Chandra X-ray Observatory to observe Saturn's moon Titan as it crossed the nebula, and found that Titan's X-ray 'shadow' was larger than its solid surface, due to absorption of X-rays in its atmosphere. These observations showed that the thickness of Titan's atmosphere is 880 km.[144] The transit of Saturn itself could not be observed, because Chandra was passing through the Van Allen belts at the time.

Notes

  1. ^ Size as measured on a very deep plate taken by Sidney van den Bergh in late 1969.[114][145]
  2. ^ Apparent Magnitude of 8.4 - distance modulus of 11.5 ± 0.5 = -3.1 ± 0.5
  3. ^ distance × tan( diameter_angle = 420″ ) = 4.1 ± 1.0 pc diameter = 13 ± 3 ly diameter

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External links

Messier 2

M2
Messier 2 Hubble WikiSky.jpg
M2 by Hubble Space Telescope; 3.5′ view
Credit: NASA/STScI/WikiSky
Observation data (J2000 epoch)
Class II
Constellation Aquarius
Right ascension 21h 33m 27s[1]
Declination -00° 49′ 24″[1]
Distance 37.5 kly (11.5 kpc)
Apparent magnitude (V) +6.3[1]
Apparent dimensions (V) 16′.0
Physical characteristics
Mass kg ( M{\odot})
Radius 87.3 ly [2]
Estimated age 13 Gyr
Other designations NGC 7089[1]

Messier 2 or M2 (also designated NGC 7089) is a globular cluster in the constellation Aquarius, five degrees north of the star Beta Aquarii. It was discovered by Jean-Dominique Maraldi in 1746 and is one of the largest known globular clusters.

Discovery and visibility

M2 was discovered by the French astronomer Jean-Dominique Maraldi in 1746 while observing a comet with Jacques Cassini. Charles Messier rediscovered it in 1760 but thought it a nebula without any stars associated with it. William Herschel was the first to resolve individual stars in the cluster, in 1794.

M2 is, under extremely good conditions, just visible to the naked eye. Binoculars or small telescopes will identify this cluster as non-stellar while larger telescopes will resolve individual stars, of which the brightest are of apparent magnitude 13.1.

Characteristics

M2 is about 37,500 light-years away from Earth. At 175 light-years in diameter, it is one of the larger globular clusters known. The cluster is rich, compact, and significantly elliptical. It is 13 billion years old and one of the older globulars associated with the Milky Way Galaxy.

M2 contains about 150,000 stars, including 21 known variable stars. Its brightest stars are red and yellow giants. The overall spectral type is F4.[1]

M2 from 2MASS sky survey

External links

References

  1. a b c d e SIMBAD Astronomical Database. Results for NGC 7089. Retrieved on 2006-11-15.
  2. distance × sin( diameter_angle / 2 ) = 87.3 ly. radius

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