500 Years of Magellanic Magnificence

"The Antarctic pole has no star of the fate of the Arctic pole, but we see many stars congregated together, which are like two nebulae, a little separated from each other- Antonio Pigafetta (1520) 


Compared to most adults, I feel like I have particularly clear memories of my childhood days and the things I learned in school. In elementary, my teachers periodically had these "units" where we'd spend weeks going into great detail about an interesting topic. The space unit in 2nd grade was obviously my favorite, but I also distinctly recall a unit on Australia in 3rd grade, where we learned all about the Great Barrier Reef, Aborigines, kangaroos, and whatever the heck Vegemite is! Or in 4th grade, my teacher taught us about the Renaissance, and how da Vinci sketched out the first helicopter centuries ahead of his time, or how the Medici family's vast banking empire dominated Italy for generations (and whose pioneering double-entry accounting system follows, or should I say, haunts me to this very day!). In 5th grade, we had a unit on the Age of Exploration, and each of us was assigned a famous explorer to give a presentation on: I got Sir Francis Drake, and I was a little disappointed that my guy wasn't the first to circumnavigate the globe; that title belongs to Ferdinand Magellan!

Magellan was actually killed in the Philippines (where my parents are from) in 1521;
curiously, my dad told me that the guy who killed him, Lapulapu, is regarded as something of a national hero in modern times!

The Magellan voyage has long been lauded as a crowning achievement of human endeavor, so naturally Magellan's name lives on in modern astronomy and spaceflight, the grand voyages of our time. But while the most notable example is the Magellan probe, launched by NASA to Venus in 1989, I thought it'd be neat to talk about two prominent astronomical features that also bear his name, especially as we mark the 500-year anniversary of Magellan's journey (1519-1522)

The Small and Large Magellanic Clouds are two dwarf galaxies gravitationally bound to the Milky Way, about 200,000 and 160,000 light years away from us, respectively. They're easily visible features in the night sky and have been known by indigenous people in South America and Africa since antiquity, and by Arab astronomers as early as the 9th century. But because they're only visible from the Southern Hemisphere, they went completely undiscovered by Europeans until Magellan's time

The Small and Large Magellanic Clouds, visible over the Paranal Observatory in Chile

Curiously, despite their obvious prominence, there's relatively little mention of the Magellanic Clouds from navigational writings of that time. As Western sailors voyaged further and further south, they encountered new star fields that they quickly needed to master, and their number one priority was to find a star in the Southern Hemisphere that would readily tell them their latitude, just like Polaris does in the Northern Hemisphere. Because the Magellanic Clouds are too diffuse to serve any navigational purpose, they were mostly ignored by contemporary navigators. In fact, there were probably plenty of Europeans who saw the Magellanic Clouds before Magellan did - Portuguese explorer Alvise de Ca'da Mosto saw the Southern Cross in 1455, and though he didn't mention any fuzzy blotches, it's possible he could've seen the Magellanic Clouds. For sure the Italian explorers Amerigo Vespucci and Andrea Corsali saw it before Magellan, because both wrote brief mentions of the clouds in 1501 and 1515

The main reason the two dwarf galaxies ended up being associated with the Magellan Expedition is because of Magellan's chronicler, Antonio Pigafetta. He was neither an astronomer nor a navigator, so he simply wrote in colorful detail about whatever caught his eye! And because the Magellan Expedition soon became famous, much of his writings survived the course of history, and over time sailors colloquially started referring to them as the Magellanic Clouds

Two pages from Pigafetta's manuscript, showing exquisite illustrations and handwriting

Today we know much more about the Magellanic Clouds than Magellan or his contemporaries ever could've imagined. The Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) are separated by about 75,000 light years, and the LMC has a diameter of 14,000 light years (roughly double the SMC). Compared to the Milky Way, the LMC is estimated to have about 1/10th the mass, and the Clouds have somewhat younger stars and a higher proportion of hydrogen and helium than heavier elements

More interestingly (in my opinion), astronomers have been trying to better describe the motion of the Magellanic Clouds relative to the Milky Way. Based on recent observations by Hubble, they appear to be much closer to us now than they have been in the past and may be moving too fast to be long-term companions of the Milky Way. In fact, we might even be witnessing the beginnings of a galactic merger with the Magellanic Clouds, which would take billions of years and would precede or coincide with the Milky Way-Andromeda collision that we know will happen in 4.5 billion years! On time scales that long, the Magellan Expedition feels like it happened just a blink of an eye ago!

Supernova SN1987A within the Large Magellanic Cloud (the bright one in the center).
It was the brightest supernova ever observed since the invention of the telescope

To learn more, check out this paper by Michel Dennefeld, titled "A History of the Magellanic Clouds and the European Exploration of the Southern Hemisphere"


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