Large and Small Magellanic Clouds

Large Magellanic Cloud

Named after the explorer, and Portuguese navigator Ferdinand Magellan, whose crew discovered these companion galaxies to the Milky Way during the first voyage worldwide (1519–22). It is called the Large Magellanic Cloud or LMC for short. It is not a cloud but a satellite galaxy of the Milky Way that lies around 50 kiloparsecs (≈163,000 light-years). 

When Edwin Hubble, an American astronomer, established the extragalactic nature of what is now called galaxies, it became plain that the Magellanic Clouds had to be separate systems.

It is Milky Way’s second- or third-closest galaxy, after the Sagittarius Dwarf Spheroidal (~16 kpc) and the Canis Major Overdensity. LMC’s diameter is about 14,000 light-years, based on the visible stars and the 10 billion solar masses. Thus, it makes one-hundredth as massive as the Milky Way and the fourth-largest galaxy in the Local Group, after the Andromeda Galaxy (M31), the Milky Way, and the Triangulum Galaxy (M33).

LMC has a stellar bar that is geometrically off-center, suggesting that the galaxy is a barred dwarf spiral before its spiral arms were disrupted, likely by tidal interactions from the Small Magellanic Cloud (SMC) and the Milky Way’s gravity. The LMC floats in space, forming long and slow dance moves around the Milky Way. The vast gas clouds slowly collapse to form new stars that light up the gas clouds in a riot of colors.

From the southern hemisphere of the Earth, the LMC is visible as a faint” cloud.” It spans Dorado and Mensa’s constellations and has a visible length of about 10° to the naked eye, or 20 times the Moon’s diameter, from dark sites away from the light pollution.

The Milky Way and the LMC are predicted to collide in approximately 2.4 billion years.


Location of Large Magellanic Clouds

Before the invention and discovery of the telescope and the different brands of it today, LMC was discovered by Magellan. However, even after the instruments allowed Galileo and 17th-century astronomers to get a closer look, it was not until several hundred years that scientists could accurately calculate the distance to the LMC, the SMC, and other nearby galaxies.

Tools as “standard candles” helped scientists to understand cosmic distances better. Previously, the LMC was considered the closest galactic object to Earth until 1994, when NASA’s astronomers found the Sagittarius dwarf elliptical galaxy. Changes in the findings again happened in 2003 when it was discovered that the Canis Major dwarf galaxy became even closer.

The LMC is a collection of dozens of galaxies known as the Local Group, or the galaxies close to the Milky Way galaxy. Andromeda galaxy is the most prominent member. It is on the northern hemisphere visible with the naked eye just north of the same name’s constellation. 

The Andromeda galaxy is 2.5 million light-years away and moves closer to the Milky Way galaxy for an eventual collision.


Small Magellanic Cloud

The small Magellanic Cloud, also called Nubecula Minor, is one of the Milky Way’s closest neighbors at about 200,000 light-years. This is a dwarf galaxy with a diameter of about 7,000 light-years. The galaxy with a total mass of approximately 7 billion solar masses contains several hundred million stars.  

The astronomers speculate that the galaxy’s central bar structure was once a barred spiral galaxy disrupted by the Milky Way and caused irregularities. The galaxy is one of the most distant objects visible to the naked eye.

Location of Small Magellanic Clouds

From most North America, northern Africa, Europe, or Asia, the SMC remained invisible from the cultures that dominated these continents except the Southern Hemisphere, where it is more prominent. In Australian aboriginal stories, it was always mentioned and helped the early Polynesian cultures navigate the seas.

The Small Magellanic Cloud is visible from the entire Southern Hemisphere. Still, it can be fully seen low above the southern horizon from latitudes south of about 15° north because the galaxy is located across both the constellations of Tucana and part of Hydrus. It looks like a faint hazy patch resembling a detached piece of the Milky Way.

The galaxy has an average apparent diameter of about 4.2°, eight times the Moon’s size, covering an area of about 14 square degrees (70 times the Moon’s). With very low surface brightness, this deep-sky object is best seen on clear moonless nights and away from city lights pollution. The SMC pairs with the Large Magellanic Cloud (LMC) that lies 20° to the east.


LMC and SMC rendered from Gaia EDR3 data 

The Large Magellanic Cloud and its neighbor and cousin, the Small Magellanic Cloud, are prominent objects in the southern hemisphere, appearing to the naked eye to be detached parts of the Milky Way. The actual distance between them is around 75,000 light-years, and they are approximately 21° apart in the night sky.

They were the closest known galaxies to our own until the discovery of the Sagittarius Dwarf Elliptical Galaxy in 1994 (as of 2003, the Canis Major Dwarf Galaxy has been discovered to be even closer, and it is now the closest neighbor).

These two galaxies’ combined mass is unknown. They both feature enormous dark matter halos, and just a portion of their gas appears to have condensed into stars. According to one estimate, the LMC’s total mass is around a tenth of the Milky Way.

In the existing observable universe, this would make the LMC a fairly big galaxy. The average mass can be deceiving since the sizes of very close galaxies are strongly distorted. In terms of mass, the LMC looks to be the fourth most massive among the local group’s more than 50 galaxies.

The Magellanic cloud system was never a part of the Milky Way proves that the SMC has been orbiting the LMC for a long time. The Magellanic system resembles the unique NGC 3109 system on the outskirts of the Local Group the most.

They diverge from our galaxy in two significant aspects, aside from their unusual structure and reduced mass. They are gaseous, with a more significant proportion of hydrogen and helium in their mass than the Milky Way. Compared to the Milky Way, the LMC and SMC’s youngest stars have 0.5 and 0.25 times solar metallicities, respectively.

Both are known for their young stellar populations and nebulae. However, like those in our galaxy, their stars range in age from very young to extremely ancient, reflecting a vast history of stellar formation.