Every once in a blue moon there’s a report about having an opportunity to spot the Aurora Borealis here in Oregon. These media reports are often quite misleading because they are accompanied by photos and videos of brilliant green ribbons spooling down from the sky. These images permeate many falsehoods about the experience of witnessing the Northern Lights, here in Oregon, and other places for that matter, and raise false expectations about what people will see and when.
There’s actually a tremendous amount of predictable science and math involved that can help determine IF you’ll see the Northern Lights, WHEN you can see the Northern Lights, HOW much of the Northern Lights you might see, and WHERE you need to be to see them.
First, let’s look at the “IF.” According to space.com, “Astronomer Galileo Galilei named the aurora borealis after the Roman goddess of the dawn, Aurora, and the Greek name for wind of the north, Boreas. The aurora australis, or the southern lights, occur over the south pole.” Since the South Pole is mostly inhospitable, viewing the southern lights is more of a challenge.
The birth of aurora events begin with the sun 93 million miles away. The sun has a tremendous amount of energy, gas and magnetic pressure. At the center of the sun the temperature is 27 million degrees Fahrenheit. The sun has spots, or magnetic centers which are cooler spots within the sun. As pressure, gas, and magnetic energy build and build, a giant bubble forms.
The pressure gets to be too much and it explodes, in a powerful flare, called a coronal mass ejection (CME). A major event can emit up to “1 × 1025 joules (roughly the equivalent of 1 billion megatons of TNT, or over 400 times more energy than released from the impact of Comet Shoemaker–Levy 9 with Jupiter.) The scope or size of a single flare could be compared to 30 earths stacked one on top of each other. These flares are the most powerful explosions in the entire solar system. These occur several times a day or approximately once a week depending upon how active the sun is. These flares cause huge bubbles of of magnetized gas to expel from the sun. The bubble of gas travels in space, rushing intensely in the solar wind, a million miles per hour. These are called geomagnetic storms. Depending upon how much force the bubble was released it can take anywhere from 17 hours up to three days to reach the earth’s atmosphere.
What also happens is the force of the flare is determined, and based on the extent of the expelled gas, the speed for which it is moving, if it picks up energy or slows down, scientists will evaluate the level of storm on a “Kp index.” The Kp numbers start at 0, and as the geomagnetic strength increases, so too does the Kp number. So Kp 0 is a weak or none existent aurora occurrence—though a 2 kp index could be seen in northern latitudes, whereas anything above 6, up to 9, is a major geomagnetic storm event which could likely cause visibility of the auroras in lower latitudes such as Washington, Oregon, or Michigan in the midwest and New York on the east coast. In Europe this would equate France or Northern Spain.
Once the energy wind hits the upper atmosphere, the wind’s charged electrons get drawn towards the centers of the earth’s poles and follow the magnetic field of Earth down to the Polar Regions where they collide with oxygen and nitrogen atoms and molecules in Earth’s upper atmosphere. “In these collisions, the electrons transfer their energy to the atmosphere thus exciting the atoms and molecules to higher energy states. When they relax back down to lower energy states, they release their energy in the form of light. This is similar to how a neon light works. The aurora typically forms 60 to 600 miles above Earth’s surface.” 60 miles is where they hover just above the earth’s surface, and the beams or curtains extend up to 600 miles into the atmosphere.
Our magnetic field guides the electrons and two ovals form over the center of the magnetic poles. Because the earth is on a curve, how far the curve extends out and down depends on the power of the storm. So, for instance, the higher up you are in latitude the more likely you are to see them; they would appear bright, and clear, and above your head, if you are in Alaska, such as Fairbanks. There, you are so far North, the latitude is beneath the region of the pole itself.
If you are further south in latitude, say Oregon, IF you were to see anything at all, it will be extremely low in the horizon and faint, appearing like nothing more than a fog cloud. You would not see the luminous green ribbons as advertised. Another myth that gets perpetuated comes from the fact that cameras pick up light better or more vibrant than the human eye. So all those colors of green, red or pink that are shown in photos, especially in lower altitudes, are only because the camera picked up on those color frequencies. You would not see them with your eyes.
The best place to observe the aurora is under an oval shaped region between the north and south latitudes of about 60 and 75 degrees. At these polar latitudes, the aurora can be seen two-thirds of the nights of a given year. The longitude is inconsequential, in that you could see the same aurora effect from Finland, Norway or Alaska at the same latitudes around the globe. The way they appear to the human eye, if you’re in a high altitude, is like tall light rays that resemble a curtain of moving, breathing, rippling, glowing light. It’s surprising actually how fast they move.
Obviously you need darkness to see them so the best times for viewing are cold clear nights, with September and October heading in towards winter and February and March heading into spring. In the northern latitudes the nights are longer in the winter months so darkness is plentiful for viewing.
The next factor about the aurora to understand is what causes the different colors. Green is the most common color with yellow, blue, violet and white. In this amazing miraculous occurrence, when the particles collide with oxygen, green and yellow bands of light are created. Interactions with nitrogen produce red, violet, and occasionally blue. “The type of collision also makes a difference to the colors that appear in the sky: atomic nitrogen causes blue displays, while molecular nitrogen results in purple. The colors are also affected by altitude. The green lights typically in areas appear up to 150 miles (241 km) high, red above 150 miles; blue usually appears at up to 60 miles (96.5 km); and purple and violet above 60 miles. These lights may manifest as a static band of light, or, when the solar flares are particularly strong, as a dancing curtain of ever-changing color.”
The basic components of math then, are to determine as to whether or not you will be able to see the northern lights, are these: How strong the solar flare was; How long the flare is taking to travel the 93 million miles (distance x speed); what latitude you are on the planet, the time of year, the amount of darkness.