did some investigation into the painting completed in April 1917 on display at the National Gallery of Canada (upper right in the above banner and above in the PowerPoint slide). He identified the stars as belonging to the constellation Cassiopeia, the big “
” in the night sky. Using this information, he identified the location where Tom must have stood while he completed the painting. Ivan called his effort “
”. I refer to the “
The following version of "
Northern Lights" was on the flip side of Tom Thomson's "
Smoke Lake - Summer 1915". There were some stars in the sky that night. I am no astronomer but Cassiopeia was also a likely candidate to explain those stabs of starlight. Instead, I wish to focus on the interesting science of northern lights.
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Northern Lights (1915.70), gift of the artist to Thoreau MacDonald.
McMichael Canadian Art Collection, Kleinburg (1968.21)
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"
Northern Lights" was a staple of the Tom Thomson Was A Weatherman presentation. I used the spring of 1917 painting but the 1915 version of "
Northern Lights" would have worked just fine as well. The science of auroras is especially intriguing and my presentation might go down one of several rabbit holes depending on the interests of the audience. It was a fun painting to discuss. What follows is my recollection of what I often talked about...
Space weather is every bit as important as atmospheric weather and becoming more so. The
Space Weather Prediction Center for the National Oceanic and Atmospheric Administration (
NOAA) is in Boulder Colorado and not far from
COMET where I worked for the last decade of my meteorological career.
The COMET class would go for a tour every year. If you are interested in the activity of the sun, coronal mass ejections or auroras, I suggest you visit the
Space Weather Link and even sign up for
Space Weather Alerts.
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| PowerPoint Slide from Tom Thomson Was A Weatherman |
The northern lights or auroras all begin with the solar wind, the continual stream of protons and electrons (collection of ionized particles referred to as plasma) from the corona of the sun. Auroras occur when the charged particles collide with gases in the Earth's upper atmosphere. In order to return to their normal relaxed state, the energized molecules release that energy as light. The excited molecules in the atmosphere emit the absorbed energy back as specific colours depending upon the difference in the excited and relaxed energy levels of the molecules involved. Billions if not trillions of flashes of light flow with the stream of charged particles from the sun. The auroras appear to dance in the sky.
Historically, the Vikings saw aurora as the bridge between earth and the gods’ heavenly home of Asgard. In Danish legends, the aurora is the result of swans that flew too far north and got trapped in ice. The shimmering lights resulted from the swans trying to free themselves from the frozen lakes by flapping their wings. Inuit described auroras as heavenly football games played by their ancestors using a walrus head as a ball. Siberians thought that the aurora was a flame kept burning by the fish god to help those who fished at night.
The northern light legends might be very interesting but sadly, are not true. The Sun is essentially a fusion bomb. The intense gravity of the sun creates extreme heat and pressure which ignites nuclear fusion through which protons fuse together to form helium atoms. This nuclear reaction releases unimaginable amounts of energy equivalent to about 10 billion hydrogen bombs per second as predicted by Einstein's famous equation relating energy to mass: "E=mc2".
The Earth's magnetic field is generated by electric currents resulting from the convection currents of a mixture of molten iron and nickel in the outer core. The geomagnetic field extends from the Earth's interior out into space... the final frontier.
The following graphic is not nearly to any scale but depicts the ingredients required to create the northern lights.
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The sun emits the energy equivalent of 2 billion times
the energy of the most powerful nuclear device, ignited
on Earth, the Tsar Bomba every second.
The geomagnetic field around the Earth protects
life from the radiation. |
The solar wind is the outward expansion of plasma (ionized gas of protons and electrons) from the Sun's outermost atmosphere, the corona. This plasma is continually heated to the point that the Sun's gravity cannot contain it. The plasma follows the Sun's magnetic field lines that extend radially outward.
A coronal mass ejection (CME) is an enormous expulsion of plasma along the magnetic fields emanating from the Sun. These eruptions are referred to as “solar flares”. Spectacular auroras result when a CME slams into the Earth causing geomagnetic storms within the earth’s magnetic field which is referred to as the magnetosphere.
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| Sunspot Image from NASA |
Dark areas on the sun's surface are regions of intense solar magnetic fields that produce volcano-like solar flares and CMEs. It takes roughly two weeks for the resulting solar winds to reach the Earth. Sunspots increase and decrease through an average cycle of 11 years. This Solar Cycle had been observed since 1600 and the science has improved through the centuries. It is interesting to note that the years 1915 through 1917 when Tom Thomson was painting his northern lights observations were marked by an increase in sunspot activity and solar flares.
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| The Eleven Year Solar Cycle |
As I prepared this Blog, I received a
Space Weather Alert. The "coronal hole" is where the sun's magnetic fields open up and allow solar wind to escape. The sunspot is dark in this ultraviolet image because the glowing-hot gas normally contained there is missing. The accompanying image of the current intense sunspot and the associated solar wind arrived with the forecast that the plasma "
should reach our planet later this week, potentially igniting a display of equinox auroras at high latitudes."
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| Sunspot March 20th, 2023 |
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PowerPoint Slide from Tom Thomson Was A Weatherman
See Ivan Semeniuk
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The aurora shimmering bands of green, red, purple, pink, blue, yellow… arise from the excitement of molecules 100 km high by the charged particles from the sun. Green is the most common resulting from oxygen molecules at around 100 km. Occasionally, the lower edge of an aurora will have a pink fringe, which is produced by nitrogen molecules at altitudes of around 100 km. Collisions with oxygen atoms higher in the atmosphere between 300 and 400 km will produce rare red auroras. An excellent analogy is that of a TV screen where electrons (from the red, blue and green electron guns) are shot at the fluorescent screen where the energized molecules respond by emitting light energy which constructs the picture we see on the TV. In the case of auroras, it is a “plasma television”.
The "
plasma TV" version of the northern lights even has
sound. But how does a process occurring in the near vacuum of the magnetosphere produce sound at the Earth's surface? How can one hear the northern lights originating from hundreds of kilometres away when I can't hear my wife from the next room? There are multiple explanations for these electromagnetic noises.
Some investigators felt that the “swishing noises” of the aurora were the result of a leaky optic nerve within the observer's brain. Tiny electrical signals from the nerves in the eyes leak into the area of the brain responsible for processing sounds and might be interpreted as sound. If you close your eyes, the “sounds of the aurora” should go away. Hmmm.
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PowerPoint Slide from Tom Thomson Was A Weatherman
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More recently, the sounds of the northern lights have been linked to the strong, shallow thermal inversions that are created on those clear, calm and very cold nights typically associated with auroras or at least the ones that people stay up late at night to watch. An electrical potential difference develops across the intense inversion. A spark ensues when the potential difference exceeds the insulating limits of the inversion. The spark heats an air channel that expands and then contracts rapidly, creating an audible sound. The swishing sound only needs to travel a hundred metres or less to your ear... versus 200 kilometres from the vacuum of the magnetosphere. This is my preferred explanation but there are admittedly others and many rabbit holes which are intriguing to investigate.
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Aurora Viewed from Space with the Plasma of the Solar
Wind Directed along the Magnet Fields of the Earth |
The mesmerizing beauty of the northern lights can be beyond compare. It is not surprising that people monitor the
Space Weather Alerts for predictions of strong and colourful geomagnetic storms and auroras in order to spend the night outside, awake and probably very cold in front of the shimmering curtains of dancing colours. Northern lights are intriguing both from space and from the ground. Tom Thomson was compelled to take his paint box outside on those frigid nights to make a record of the beauty that he witnessed.
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Tom Thomson's View from the ground up...
Tom observed the most common green auroras
resulting from oxygen molecules at around 100 km. |
It is tempting to investigate the many branches of science that start with those fiery lights in the night sky. Following those many interests down multiple rabbit holes would fill several books let alone a blog. The result would be an explanation of the natural world revealing the facts that we live a safe distance from a fusion reactor, within a natural paradise on a spinning globe with a molten nickel-iron outer core while shielded from exorbitant radiation by a magnetic field... Let's not go there .. yet.
Mr. Semeniuk responded politely: "That is a good question. It doesn't make the painting any more beautiful, that's for sure. It doesn't increase our appreciation of the art, but it does say something about Thomson's commitment to representing a real place in time. He wasn't just making this stuff up. He was responding to the environment, including transient things like the northern lights. He was excited by them and he really rendered them truly."
Ivan Semeniuk exactly echoed my most sincere sentiments, but I also wish to emphasize the importance of science and knowledge. As an entitled society, we do not tend to appreciate or preserve what we do not understand. The message within the "Big Yellow Taxi" written by Canadian singer-songwriter Joni Mitchell in 1970 is even more valid now fifty years later.
Perhaps society is awakening to the importance of the natural world. Is it too late? Previous extinction events were caused by natural phenomena. The sixth mass extinction is primarily driven by human activities including the unsustainable use of land, water, air and energy. Simultaneously, the accumulated impacts of the Industrial Age since 1850 are fuelling anthropogenic climate change. The science is clear and it is vital that the electorate becomes informed to ensure that the elected politicians follow through and provide real leadership.
Eduard Zukowski, who worked at the Art Gallery of Ontario, split the panel and cleaned the surfaces of both sides. He also removed the "X" from Smoke Lake. In 2006 the heirs of the Patterson estate were uncertain whether their sketch was by Thomson., so they brought Northern Lights to the author (Joan Murray), who was then interim executive director of the McMichael Canadian Art Collection. When they were assured about the authenticity of their work and shown the other half, they placed it at auction, where the present owner purchased it."
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