How was the sun’s corona discovered?

Unveiling the Sun’s Crown: A Human Story of the Corona’s Discovery

The Sun. We’ve stared at it for millennia, haven’t we? But while its bright surface blazes in plain sight, its wispy outer atmosphere, the corona, has always been a bit of a hide-and-seek champion. Imagine a pearly white crown stretching millions of kilometers into space – that’s the corona. The problem? The Sun’s own glare usually keeps it hidden. It’s only during those magical moments of total solar eclipses, when the Moon plays peek-a-boo and perfectly blocks the Sun, that the corona puts on its dazzling show.

Early Glimpses and a Few Misunderstandings

Believe it or not, someone spotted the corona way back in 968 AD! Leo Diaconus described it as a “dim and feeble glow” during an eclipse. But, for a long time, folks weren’t quite sure what they were seeing. Was it part of the Sun? The Moon? Some weird trick of the light? In 1724, Giacomo F. Maraldi, an astronomer with a hunch, suggested that this aura actually belonged to the Sun, not the Moon. Before that, many astronomers thought they were just seeing the Moon’s atmosphere or some kind of optical illusion.

Then, in 1809, José Joaquín de Ferrer, a Spanish astronomer, watched the 1806 solar eclipse in New York and gave it a name: “corona.” He figured it was part of the Sun. Still, even with these observations, the corona kept its secrets locked up for years.

The Spectroscopic Game Changer

Things really took off in the mid-19th century with the arrival of spectroscopy. This was a game changer. Think of it like a prism that splits light into its colors, revealing the chemical makeup of whatever’s emitting the light. During the 1869 solar eclipse, William Harkness, an American astronomer, spotted a strange green line in the corona’s light. This line was a mystery! It didn’t match any known element on Earth. The scientists scratched their heads and even came up with a name for a new element: “coronium.”

But the real breakthrough came in the 1930s and 40s. In 1930, Bernard Lyot invented the coronagraph. Imagine a telescope that creates its own mini-eclipse, blocking out the Sun’s disk so you can see the corona anytime, eclipse or not! Then, in 1940, Bengt Edlén, building on Walter Grotrian’s work, cracked the code. That mysterious green line? It was highly ionized iron – iron atoms that had lost a whopping 13 electrons! This meant the corona was unbelievably hot, way hotter than the Sun’s surface, reaching millions of degrees Celsius. Talk about a surprise!

The Crazy Hot Corona and the Man Who Figured It Out

The fact that the corona is so incredibly hot – much hotter than the Sun itself – presented a major head-scratcher. Usually, heat flows from hot to cold, right? So how could the corona stay so scorching? This became the “coronal heating problem,” and it’s still one of the biggest puzzles in solar physics.

While Edlén figured out the ionized iron part, it was Hannes Alfvén who really drove home the idea of the corona’s insane temperature. Back in 1941, he published a paper in some Swedish journal basically saying, “Hey, this corona thing is heated to an extremely high temperature!”

Today’s Corona

Today, we’ve got some seriously cool tools to study the corona. Space-based observatories like SOHO and the Parker Solar Probe are giving us details we could only dream of before. We’re seeing the corona’s crazy complex structure, its wild behavior, and how it creates the solar wind, that stream of charged particles that washes over our solar system. And the Parker Solar Probe? It’s flown closer to the Sun than any spacecraft ever, sending back invaluable info about the corona’s magnetic fields and plasma.

The journey to understand the Sun’s corona has been quite the ride, a story of centuries of observations, clever inventions, and some seriously bright minds. From those early eclipse sightings to the high-tech measurements we’re making today, each step has brought us closer to solving the mysteries of this amazing part of the Sun. And who knows what we’ll discover next?