Magellanic Clouds
The two
Magellanic Clouds are
irregular dwarf galaxies orbiting our
Milky Way galaxy, and thus are members of our
Local Group of galaxies.
They were certainly known since the earliest times by the ancient southerners.The first preserved mention of the
Large Magellanic Cloud was by Persian astronomer
Al Sufi, who in
964, in his
Book of Fixed Stars, calls it
Al Bakr, the
White Ox of the southern Arabs, and points out that while invisible from Northern
Arabia and
Baghdad, this object is visible from the
strait of
Bab el Mandeb, at 12°15' Northern
latitude.Eventually, it was
Ferdinand Magellan and his discovery expedition who brought them to western knowledge in
1519.
The
Large Magellanic Cloud and its neighbour and relative, the
Small Magellanic Cloud, are conspicuous objects in the southern hemisphere, looking like separated pieces of the
Milky Way to the naked eye. Roughly 21
° apart in the night sky, the true distance between them is roughly 75,000
light-years. Until the discovery of the
Sagittarius Dwarf Elliptical Galaxy in
1994, they were the closest known galaxies to our own.
Observation, and theoretical evidence suggests that the LMC and SMC have been greatly distorted by
tidal interaction with the Milky Way as they
orbit around it; streams of neutral hydrogen connect them to the Milky Way and to each other, and both resemble disrupted
barred spiral galaxies.
(Zeilik) However, their
gravity has affected our Galaxy as well, distorting the outer parts of the
galactic disk. (Chaisson and McMillan)
Aside from their different structure and lower mass, they differ from our Galaxy in two major ways. First, they are gas-rich; a relatively higher fraction of their mass is hydrogen and
helium compared to the Milky Way.[
1]. They are also more metal-poor than the Milky Way; the youngest
stars in the LMC and SMC have a
metallicity of 0.5 and 0.25 times solar, respectively.[
2] Both are noted for their
nebulae and young
stellar populations, but as in our own Galaxy their stars range from the very young to the very old, indicating a long
stellar formation history.(Chaisson and McMillan)
The Large Magellanic Cloud was host galaxy to a
Supernova (
SN 1987A), the brightest observed in over three centuries.
*Eric Chaisson and Steve McMillan,
Astronomy Today, (Englewood Cliffs: Prentice-Hall, Inc., 1993), p. 550.
*Michael Zeilik,
Conceptual Astronomy, (New York: John Wiley & Sons, Inc., 1993), pp. 357-8.
*
Magellanic Clouds Working Group*
Local Group*
Irregular Galaxies*
Magellanic Stream*
Magellanic Bridge
