By Mary Stewart Adams, Headlands Program Director
The Northern Lights are by far one of the most sought-after phenomena in the night sky, but despite years of scientific research and the best-laid plans of stargazers everywhere, their occurrence remains as nearly elusive today as it was for the ancients, who described the lights as the Aurora Borealis, which is to say, they are the colors that are born of the wind as it wings across the morning sky, herald triumphant of the rising Sun.
The study of what causes these colors that are born of the wind is an evolving narrative that reads like the most wildly-imagined science fiction novel, including as it does descriptions of things like the interplanetary magnetic field that is embedded in continuous streams of solar wind; coronal mass ejections (CMEs) that erupt during peaks in the sunspot cycle and are measured with Kp Indices by the Kiruna Magnetogram; or even the co-rotating interaction regions (CRIs) that appear in areas of a weakened magnetic field on the Sun’s surface when the sunspot cycle is low. Huh?
In layman’s terms, it goes something like this: Solar wind originates with the Sun and is continuous through our planetary system. While the Sun’s light travels at the speed of light and arrives at Earth exactly 8 minutes and 20 seconds after it leaves the Sun, solar wind is made up of electrons, protons, and alpha particles that travel through space much slower than sunlight, at rates that vary according to temperature and density. Further, solar wind is affected by activity on the Sun’s surface, where things are not uniform and there are naturally-occurring spots and weak regions in the magnetic field. These sunspots and magnetic regions are in rhythmic motion about the Sun’s uppermost layer, and when they are active while facing earthward, they can cause a change in the continuous flow of solar wind, which may then result in a sparking and stirring of aurora once this charged solar plasma arrives at Earth.
Scientists watching the Sun’s activity in order to make predictions about Northern Lights have to read the CMEs and CRIs in terms of strength, velocity, and density in order to say things like: “Hey everybody, there’s activity on the Sun, which means a possible aurora for northern latitudes could happen in 24 hours…” Add to this the time of year and the axial tilt of the Earth, together with Earth’s own non-uniform magnetic field, and the local weather, and it becomes painfully evident just how tricky it is to answer the single-most asked question at Headlands, “When can I see the Northern Lights?”
All that said, if you hope to catch the Northern Lights at Headlands, here’s what you should know:
Strength of solar wind
Given our latitude at 45 degrees north, it is possible to see aurora when the index used to measure the solar wind, called the Kp index, from the German for “Planetarische Kennziffer” or “planetary index”, is at 5 or above. If you are traveling from a distance on short notice, then this bit of information is key to sound decision-making (you can find the Kp index at websites like www.spaceweatherlive.com).
Time of Year
Statistics gathered over the last 75 years of aurora research show that due to Earth’s axial tilt, the Northern Lights are more likely to occur at the times of Equinox in Spring and Fall than at other times of year, although this, too, is variable and inconsistent, and we have seen beautiful aurora at other times of year, especially including Summer Solstice in 2016
Time of Night
Around the poles of the Earth there is what’s called an auroral oval. The thicker part of it swings our way after midnight, which is usually when an aurora will be strongest, although this, too, is not iron-clad, and at Labor Day weekend in 2016 aurora visibility over Headlands started as early as 10 pm
Phase of Moon
Another variable factor in the equation is moonlight. A really strong aurora will not be diminished by moonlight, no matter the phase, but a gibbous or Full Moon can send a lot of light into the night, diminishing views of weaker aurora. Moon phase is also an important consideration for stargazing in general (see Plan B, below), since the light reflecting off the Moon can also diminish the starshine.
Cloudy skies, rain, snow~all of this interferes with views of the night sky and visibility of the aurora.
Follow those in the know on social media
If ever there was a handy purpose for the immediacy of social media, chasing the aurora is it (try sites like www.solarham.net). There are tons of photographers throughout the Great Lakes region that use platforms like Facebook and Twitter to communicate with one another quickly once Northern Lights are active in their area. Two Facebook pages we can recommend are Great Lakes Aurora Hunters and Michigan Aurora Hunters.
Solid Plan B
Probably the least gratifying but most realistic of all of the above is crafting an alternative plan if the aurora doesn’t show. As with anything that involves the outdoor environment, check the forecast and dress for the weather; consider the Moon phase (a Full Moon will knock out the fainter stars and views of the Milky Way, but it’s a spectacular sight to catch the Moon setting into Lake Michigan); find out what time sunset is and avail yourself of a star map like Abrams Planetarium Sky Calendar from MSU so that you can familiarize yourself with what’s overhead before you arrive at the dark sky park and find yourself reaching for phones and flashlights that aren’t allowed in the viewing area; and finally, set out knowing that any attempt to experience the wonders of the night sky will bring its own reward, in due time.
The people of the Ancient world believed that the forces of nature were the sacred expression of a divine world order full of unfathomable mysteries, and historical record suggests that those to whom nature revealed itself had a certain responsibility within their communities to be leaders and bearers of the highest ideals. To witness the wind, bearing color as it flew across the sky meant to join a unique position among those peerless few who knew what it meant to be a herald of the rising Sun.
The lead photo accompanying this article is by Shawn Malone of Lake Superior Photography, who will host our March 18, 2017 astrophotography workshop at Headlands