Across the Universe: Forbidden Transitions
avatar

This column was first published in The Tablet in February 2011

The aurora borealis as seen from Michigan's upper peninsula. Alas, I did not take this photo!

Earlier this month [2011], NASA satellites observed a set of flares on the surface of the Sun and predicted that glorious aurorae would soon be visible – a rare sight anywhere in Europe south of Scandinavia. But that was the week I was visiting my brother in northern Michigan, so I resolved to take a moment to look for them.

The Northern Lights are a marvelous sight. The easiest to see are sheets of light in the northern sky, moving like curtains in the wind. If they’re bright enough, you can see colors, mostly green, swirling like a light show at a 60’s rock concert.

The science behind them is equally fascinating. Electrons and protons burst from the Sun in explosions of an expanding plasma as large as planet Earth. Hot enough to overcome the Sun’s gravity, as they move from the Sun they feel even less gravity; they move further, move faster, feel less gravity, move even faster, even further, until they’re part of a supersonic Solar Wind filling interplanetary space. Because it is electrically charged, it drags the Sun’s magnetic field with it, warping the familiar bar-magnet dipole into a twisted spiral.

And then this plasma and magnetic field hits the Earth’s magnetic field, pushing and dragging it about, and dumping many of those charged particles into Earth’s Van Allen belts.

All these charged particles follow the dipole magnetic field of the Earth, pouring into the north and south magnetic poles. When they hit, they rip the electrons off the atoms in Earth’s upper atmosphere. Then the electrons recombine with those atoms they just left, emitting light as electrons jump from one energy state to another; different colors for different energy states. Most of the emission is in a range beyond what the human eye can see, but one of those colors is a pale green: the main light of the auroras, borealis and australis, visible if you’re close enough to the magnetic poles where all these ions are hitting.

The green light comes from a transition that, according to the rules of physics, shouldn’t take place. (It violates spin parity.) But it happens anyway; just not too often. What’s the use of a rule that doesn’t work? Actually, it’s a very useful rule; it’s just that nature’s more complicated sometimes. Ultimately, all the rules of physics are like that. They’re useful, but they don’t quite explain everything. You have to understand where they apply, and know how to use them intelligently. Being a physicist (like being a Catholic) is more than just knowing a lot of rules.

Look at a map and you’ll see that even the northernmost part of Michigan is at a far more southern latitude than the UK. But it’s much closer to the Earth’s magnetic north pole, which is located in northern Canada. Even though London is five degrees further north, Marquette is 500 km closer to the magnetic pole. As a result, the auroras are more commonly seen there.

It’s also thousands of kilometers from any ocean, so the weather is significantly colder... as I noticed when I went out looking for the aurora. I also noticed what the news reports forgot to mention, that the nights of the maximum aurora were also the nights around the full Moon.

Shivering in the cold, I watched the stars of Orion play tag with low-lying clouds, swept about by the west wind. The moonlight illuminated the clouds from above, and from below they were lit by the nearby bonfires set to guide the annual midnight dogsled races, being held that night. If there had been a glow of green between the stars I would never have seen it.

Still, the nighttime sky is a busy place, and a marvelous inducement to wonder... about light and dark and forbidden transitions.

Br. Guy Consolmagno

About Br. Guy Consolmagno

Brother Guy Consolmagno SJ is Director of the the Vatican Observatory and President of the Vatican Observatory Foundation. A native of Detroit, Michigan, he earned undergraduate and masters' degrees from MIT, and a Ph. D. in Planetary Science from the University of Arizona; he was a postdoctoral research fellow at Harvard and MIT, served in the US Peace Corps (Kenya), and taught university physics at Lafayette College before entering the Jesuits in 1989.

At the Vatican Observatory since 1993, his research explores connections between meteorites, asteroids, and the evolution of small solar system bodies, observing Kuiper Belt comets with the Vatican's 1.8 meter telescope in Arizona, and applying his measure of meteorite physical properties to understanding asteroid origins and structure. Along with more than 200 scientific publications, he is the author of a number of popular books including Turn Left at Orion (with Dan Davis), and most recently Would You Baptize an Extraterrestial? (with Father Paul Mueller, SJ). He also has hosted science programs for BBC Radio 4, been interviewed in numerous documentary films, appeared on The Colbert Report, and for more than ten years he has written a monthly science column for the British Catholic magazine, The Tablet.

Dr. Consolmagno's work has taken him to every continent on Earth; for example, in 1996 he spent six weeks collecting meteorites with a NASA team on the blue ice regions of East Antarctica. He has served on the governing boards of the Meteoritical Society; the American Astronomical Society Division for Planetary Sciences (of which he was chair in 2006-2007); and IAU Commission 16 (Planets and Satellites). In 2000, the small bodies nomenclature committee of the IAU named an asteroid, 4597 Consolmagno, in recognition of his work. In 2014 he received the Carl Sagan Medal from the American Astronomical Society Division for Planetary Sciences for excellence in public communication in planetary sciences.

This blog is made possible by contributions from visitors like yourself. PLEASE help by supporting this blog.

Get the VOF Blog via email - free!

Enter your email address to subscribe to this blog and receive notifications of new posts by email.


Comments

Across the Universe: Forbidden Transitions — 1 Comment

  1. My wife and I spent many a night after we met, on a Lake Superior beach, watching the aurora dome overhead, and whip wildly from horizon to horizon. I’ve seen it 4 times from my home, 24 miles north of Detroit. I was fortunate enough to get some great pics of the aurora in 2011 – these were taken a short distance from my home:

    The lights on the bottom are cars on I-94, eastbound towards Port Huron – those poor motorists must have thought the sky was on fire!

Leave a Reply