Large Magellanic Cloud
From Wikipedia, the free encyclopedia
The Large Magellanic Cloud |
|
| Observation data: J2000 epoch | |
|---|---|
| Constellation: | Mensa/Dorado |
| Right ascension: | 05h 23m 34.5s[1] |
| Declination: | -69° 45′ 22″[1] |
| Redshift: | 278 ± 3 km/s[1] |
| Distance: | 168 ± 3 kly (51.5 ± 0.9 kpc)[2] |
| Type: | SB(s)m[1] |
| Apparent dimensions (V): | 10°.75 × 9°.17[1] |
| Apparent magnitude (V): | 0.9[1] |
| Notable features: | Brightest galaxy orbiting Milky Way Galaxy |
| Other designations | |
| LMC, ESO 56- G 115, PGC 17223[1] | |
| See also: Galaxy, List of galaxies | |
The Large Magellanic Cloud (LMC) is a dwarf galaxy that orbits our own galaxy, the Milky Way. It is at a distance of about fifty kiloparsecs (≈160,000 light-years). It has about 1/20 the diameter of our galaxy and 1/10 the number of stars (i.e. about 1010 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. It is named after Ferdinand Magellan, who observed it and the companion Small Magellanic Cloud (SMC) in his circumnavigational voyage around the Earth. However, it was already mentioned around 964 by 'Abd Al-Rahman Al Sufi in his Book of Fixed Stars.[citation needed]
Contents |
[edit] 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. 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).[2]
[edit] Features
Like many irregular galaxies, the LMC is rich in gas and dust, and it is currently undergoing vigorous star formation activity.[3] 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.[4] 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.[5] Supernova 1987a—the nearest supernova in recent years—was also located in the Large Magellanic Cloud.
[edit] View from the LMC
From a hypothetical planet 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 that makes studying in the Milky Way's plane difficult from Earth.[6] Its neighbor the SMC would be about magnitude 0.6, substantially brighter than the LMC appears to us.
[edit] See also
[edit] References
- ^ a b c d e f g NASA/IPAC Extragalactic Database. Results for Large Magellanic Cloud. Retrieved on 2006-10-29.
- ^ a b Gieren, Wolfgang; Storm, Jesper; Barnes, Thomas G., III; Fouqué, Pascal; Pietrzyn'ski, Grzegorz; Kienzle, Francesco (2005). "Direct Distances to Cepheids in the Large Magellanic Cloud: Evidence for a Universal Slope of the Period-Luminosity Relation up to Solar Abundance". The Astrophysical Journal 627 (1): 224-237.
- ^ Thomas T. Arny, Explorations: An Introduction to Astronomy, 2nd ed., (Boston: McGraw-Hill, 2000), 479.
- ^ Robert Burnham, Jr. Burnham's Celestial Handbook: Volume Two, (New York: Dover Publications, Inc., 1978), 837.
- ^ Ibid., 840-848.
- ^ 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).
[edit] External links
 Galactic Core: Center of the Milky Way |
