Astro Bob: Auroras may bring in spring
Keep an eye on the northern sky Friday and Saturday nights, March 19-20. You may catch sight of the aurora as we make the transition from winter to spring.
We've had a good run of the aurora borealis this month with modest but nice displays on March 2, 12 and 13. With a little luck we'll see a fourth act Friday and Saturday nights, March 19 and 20. On the 19th, conditions will be "active" between about 7 p.m. and 1 a.m. Central Daylight Time then increase to a minor geomagnetic storm Saturday during early evening hours.
Minor storms are typically visible from the northern half of the northern border states and Canada. They often begin with a faint, greenish arc hovering low above the northern horizon. Activity typically picks up after 10 o'clock when a second arc can appear, brighten and then dissolve into a series of taffy-like rays and spikes.
During minor storms the rays stretch upward and slowly swirl across the lower third of the northern sky, often moving from east to west. One of my favorite sights is watching a single ray suddenly narrow and intensify into a laser-like beam then quickly fan out and fades away.
That's why we watch the northern lights. While you can sense which way a display is headed, either toward a build-up or a slow-down, there are always little surprises along the way that make you stick around for more. Like not being able to put the book down because the story you're reading takes so many unexpected twists and turns. If the aurora happens either night — and there's always the chance it won't materialize at all — find a place with a dark, open northern horizon in advance.
To aid you in your quest, use this interactive light pollution map to find the darkest possible northern sky. When the map pops up, use your mouse to drag it to your location and the scroll to zoom in. The best places are colored purple, gray and blue. Avoid red, orange and yellow-colored areas. I mostly pull off onto rural roads with good views to the north and bring a telescope or binoculars to look at the sky in case the aurora takes its sweet time showing up. Earlier this month, I arrived at my "spot" at 8:30 but had to wait until 10:15 p.m. for the lights to wake from their slumber and put on a great little show.
The sun constantly burps and blows clouds of subatomic particles into space — a mix of electrons and protons called plasma. Solar flares, massive thermonuclear blasts, can kick out extremely fast-moving clouds of plasma that stir up brilliant northern lights displays. Gaps in the sun's outer atmosphere or corona called coronal holes can also bathe the Earth in this invisible bubble bath.
That's what's behind the current forecast — a coronal hole and also something called a co-rotating interactive region or CIR. Simply put, a CIR occurs when a faster solar particle wind from the sun (from a coronal hole) catches up to and slams into the everyday particle wind from the sun. This creates a dense wave of particles with the potential to link into Earth's magnetic field. Once a connection is made, the stuff rains down at high speed into the atmosphere and excites oxygen and nitrogen atoms to glow. You heart, too.
The Italian polymath Galileo came up with the term aurora borealis, named for Aurora, the Roman goddess of dawn and Boreas, the Greek god of the north wind. Like many, he thought the aurora was sunlight reflecting from the atmosphere, similar to what occurs during twilight. It wasn't until the early 1900s when Norwegian scientist Kristian Birkeland discovered the real cause of the mysterious lights. Birkeland and his assistants spent countless hours on cold, windy mountaintops in Norway from 1899-1900 mapping electrical and magnetic fields during auroral displays.
Humans have marveled at the northern lights since our ancestors first looked up in the sky and wondered what the heck was going on. The oldest-known, possible auroral sighting comes to us from China from 2600 B.C.:
"Fu-Pao, the mother of the Yellow Empire Shuan-Yuan, saw strong lightning moving around the star Su, which belongs to the constellation of Bei-Dou, and the light illuminated the whole area."
The oldest definitive aurora record dates precisely to March 12-13, 567 B.C. in Babylonia during the 37th year of King Nebuchadnezzar II. Official astronomers described an unusual "red glow" in the sky that night and dutifully recorded it on a clay tablet. According to NASA's History of Auroras site, the earliest known depiction of the aurora may be the loopy outlines , called macaronis, in a 30,000 B.C. Cro-Magnon cave-drawing.
The aurora itself is ancient, going back to the days of the dinosaurs and beyond. Witnessing the playfulness and energy of those colorful arcs and spikes connects us to things that endure across the ages.
Which reminds me of another long-celebrated event — the coming of spring. That happens at 4:37 a.m. CDT March 20 when the sun crosses the celestial equator (an imaginary extension of Earth's equator into the sky) moving north. On that date it will stand midway between its lowest and highest points in the sky. Day and night will be equal (12 hours) no matter where you are on the planet.
Snow may still be thick in the woods here... but not for long.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob .