In June 2015, I took my first photo of an aurora (Northern Lights) using a camera mounted on a tripod to get a long exposure and was blown away by the colors that were not visible to eye. All I could see in the sky was a brighter-than-usual glow. The experience got me hooked on chasing auroras!
In the high latitudes, at places such as Iceland, Alaska, Norway, auroras are fairly common and the colors bright and visible. Unfortunately, I have yet to experience such a spectacle – it’s on my bucket list! In the mid-latitudes, such as the northern half of the US, catching an aurora is much more difficult. I think that’s why it’s called “aurora chasing” – you have to work at it! There are several challenges that must be met and it can be frustrating at times.
I am not an expert on the science and will not dive into the details, but let’s set the stage with the phenomenon which causes auroras in the first place. Like all stars, our sun is a fiery ball of super-heated plasma. For the past couple of centuries, we have noticed that the number of sunspots ebbs and flows with a cycle of approximately 11 years. We still don’t know why, but it’s consistent, with some cycles stronger than others. Along with sunspots, when the Sun is active, it creates solar storms where some of the highly magnetized plasma gets ejected into space. These are called coronal mass ejections (CMEs). We now have instrumentation, both ground- and space-based, that detects and monitors CMEs. If a CME is aimed at the Earth, then we have a potential for the magnetized plasma to interact with our magnetic shield and this is what creates auroras. It can take anywhere from 2 to 4 days for a CME to reach the Earth given its velocity. Here is the first challenge with forecasting auroras: we can detect CMEs on the Sun, but we must guess that it’s Earth-directed. After that, it’s a waiting game to see how close and how intense the CME is. We have a couple of satellites between us and the Sun to detect how strong the incoming CME is, but given their position, we only get a 30 to 60 minute reading ahead of Earth impact.
The next challenge is that a CMEs have a complex magnetic structure that we are just beginning to understand how it interacts with our magnetic shield. Magnets have polarity (north, south) and for an aurora to form, the CME has to be oriented to the south. Different parts of the CME structure can have varying polarities and create fluctuations where the aurora can suddenly flip on or off. Remember that we can only observe polarity and strength within a 30-to-60-minute forecast.
The above is a very high-level summary of the heliophysics behind auroras. Websites, such as SpaceWeatherLive, summarize and simplify the metrics and models from agencies, such as NOAA. One real-time measure of the intensity of the solar wind is called the Kp-Index. This, along with the polarity (Bz) can be a good predictor if it’s worth checking for an aurora. For Massachusetts, I have found that the Kp-Index needs to be at least 5. One of the best sources for technical details and 4 day forecasts is the videos produce by the Space Weather Woman. Dr. Tamitha Skov is a physicist who is pioneering the idea that Space Weather (such as CMEs and auroras) should be forecast, much like terrestrial weather forecasts. She has built up a highly active community on Twitter of aurora chasers, such as myself.
The website is not always reliable, but there is a webcam in Maine pointed at Mt. Katahdin that can pick up the auroras. Generally, if the camera can see it, then we have a good chance here in Massachusetts.
Here are some more Earthly challenges for observing an aurora:
Clouds: if they are covering the northern horizon, the best you can get is some interesting glowing clouds that can be easily confused with reflections from terrestrial lights.
The moon: if the moon is out and near full in its cycle, then the moonlight will wash out the faint light of the aurora. This eliminates about one-quarter or more of the available nights.
Dark skies and clear northern horizon: Light pollution from cities to the north can easily overwhelm an aurora and, in the mid-latitudes, the aurora will be close to the horizon.
A camera capable of taking long exposures, at least 3 seconds or more, and a tripod. A wide-angle lens is better.
The bottom line is that there are several conditions that must be met to catch an aurora in Massachusetts. My success rate is very low – less than 5% of the time from hearing about an Earth-directed CME will I get a chance to capture an aurora. This is much too low a probability to let others know, other than “it’s happening NOW!” And, even then, it’s usually in the middle of the night. 😊
For me, I’m addicted and willing to do whatever it takes. Being retired means no commitments and late nights are not a problem. Also, I am lucky to live within 100 yards of a good spot to catch the auroras and can monitor their arrival by sticking a camera up to a window.