LARGE MAGELLANIC CLOUD

The 'Large Magellanic Cloud' (LMC) is a dwarf galaxy that orbits our own galaxy, the Milky Way. It lies at a distance of about 50 kiloparsecs (≈160,000 light-years) away. It has about one-tenth as many stars as our Galaxy (i.e., about $10^\{10\}$ stars). While somewhat irregular in morphology, it does have some traces of a spiral structure. The NASA Extragalactic Database lists the Hubble sequence type as Irr/SB(s)m.
The LMC may once have been a barred spiral galaxy that was disrupted by the Milky Way to become somewhat irregular. It still contains a central bar structure, and is the fourth largest member of the Local Group, following the Andromeda Galaxy (M31), the Milky Way, and the Triangulum Galaxy (M33).
It is visible as a faint object in the night sky of the southern hemisphere, straddling the border between the constellations of Dorado and Mensa.

Contents

History

Distance

Features

View from the LMC

See also

Notes

References

External links

History

★ The first recorded mention of the Large Magellanic Cloud was by the Persian astronomer Abd Al-Rahman Al Sufi in his ''Book of Fixed Stars'' around 964AD.^[1][2]

★ The next recorded observation was in 1503-4 by Amerigo Vespucci in a letter about his third voyage. In this letter he mentions "three Canopes, two bright and one obscure”; the “bright” refers to the two Magellanic Clouds, and the "obscure" refers to the Coalsack.^[3]

★ Fernando de Magellan, on his voyage in 1519, was the first to bring the LMC into common Western knowledge. The galaxy now bears his name.²

Distance

As with all galaxies, establishing a precise distance to the LMC is a challenge, and estimates have varied substantially over the years. The main difficulty is due to the uncertainty of the parallax estimates of the standard candles in our galaxy which are used to calibrate extragalactic distance estimates, such as Cepheid and RR Lyrae variables; another is the possible influence of the LMC's lower metallicity on the luminosity of those variables. With the occurrence of SN 1987A in the LMC, scientists were given a unique opportunity to directly measure the distance to the LMC, based on the time taken for the light emitted by the supernova to illuminate a distant ring of gas surrounding it. This resulted in an estimate of the distance from Earth to the barycenter of the LMC of 52.0 ± 1.3 kpc, and also gave new data for the zero point of the Cephid distance scale, and the Hubble constant.^[4] This and other improved estimates over the past decade have settled on a range from 155,000 to 165,000 light-years, with a most recent distance modulus estimate of 18.56 ± 0.04, which is roughly 168 ± 3 kly (51.5 ± 0.9 kpc).^[5]
Based upon the above distance, one may estimate that the absolute magnitude of the LMC is -17.7 and estimate that the diameter of LMC at the widest point is 31.9 ± 0.6 kly.

Features

Like many irregular galaxies, the LMC is rich in gas and dust, and it is currently undergoing vigorous star formation activity.^[6] As such, it is home to the Tarantula Nebula, the most active star-forming region in the Local Group.
The LMC is full of a wide range of galactic objects and phenomena that make it aptly known as an "astronomical treasure-house, a great celestial laboratory for the study of the growth and evolution of the stars," as described by Robert Burnham, Jr.^[7] Surveys of the galaxy have found roughly 60 globular clusters, 400 planetary nebulae, and 700 open clusters, along with hundreds of thousands of giant and supergiant stars.^[8] Supernova 1987a—the nearest supernova in recent years—was also located in the Large Magellanic Cloud.

View from the LMC

From a viewpoint in the LMC, the Milky Way would be a spectacular sight. The galaxy's total apparent magnitude would be -2.0—over 14 times brighter than the LMC appears to us on Earth—and it would span about 36° across the sky, which is the width of over 70 full moons. Furthermore, because of the LMC's high galactic latitude, an observer there would get an oblique view of the entire galaxy, free from the interference of interstellar dust which makes studying in the Milky Way's plane difficult from Earth.^[9] The Small Magellanic Cloud would be about magnitude 0.6, substantially brighter than the LMC appears to us.

See also

★ Large Magellanic Cloud in fiction

★ Magellanic Clouds

★ Small Magellanic Cloud

★ SN 1987A

Notes

1. Apparent Magnitude of 0.9 - distance modulus of 18.56 ± 0.04 = -17.7


2. distance = × tan(diameter_angle) = 168 ± 3 kly × tan(10°.75) = 31.9 ± 0.6 kly diameter

References

1. Observatoire de Paris (Abd-al-Rahman Al Sufi)
2. Observatoire de Paris (LMC)
3. Observatoire de Paris (Amerigo Vespucci)
4. New Distance Determination to the LMC
5. Direct Distances to Cepheids in the Large Magellanic Cloud: Evidence for a Universal Slope of the Period-Luminosity Relation up to Solar Abundance, Gieren, Wolfgang; Storm, Jesper; Barnes, Thomas G., III; Fouqué, Pascal; Pietrzyn'ski, Grzegorz; Kienzle, Francesco, , , The Astrophysical Journal, 2005
6. Thomas T. Arny, ''Explorations: An Introduction to Astronomy'', 2nd ed., (Boston: McGraw-Hill, 2000), 479.
7. Robert Burnham, Jr. ''Burnham's Celestial Handbook: Volume Two'', (New York: Dover Publications, Inc., 1978), 837.
8. Ibid., 840-848.
9. Some of the figures in the "View" section were extrapolated from data in the Appendix of Chaisson and McMillan's ''Astronomy Today'' (Englewood Cliffs: Prentice-Hall, Inc., 1993).

External links

★ NASA Extragalactic Database

★ Encyclopedia of Astronomy entry

★ SEDS LMC page