Tom Thomson's Moonlight

Tom Thomson: Moonlight, 1913-14

Art is essentially about observing light and how it plays across the composition. Artists can also benefit from listening to what that light might be saying. Light contains a lot of science which seems deceptively simple... 

In Tom Thomson's Rainbow we investigated light refracting and reflecting from small, spherical rain drops to produce the multi-coloured rainbows. 

Refraction - Light is dispersed into its component wavelengths
as a result of differing transmission speeds in the different media

Refraction is the bending of a light when it travels at an angle from one medium into another. This refraction of light is caused by the difference in transmission speed in the other media. Refraction separates the white light, into its component colours sorted by wavelength. Short (violet) wavelengths bend by the most while long (red) wavelengths charge ahead on a straighter path.

Reflection  occurs when at least a part of the oncoming light remains in the initial medium at the boundary with another medium. 

Reflection from Surfaces Explained
Light reflected from a surface determines how we perceive it.
The accompanying graphic illuminates three different surfaces
with white light  - comprised of all of the colours of the rainbow.

The light in Tom's Moonlight took about 8 minutes and 20 seconds to get from the sun to the moon and another 1.3 seconds to reflect from the moon to his eye. How Tom saw and painted the moon was also  influenced by what was in the atmosphere. The moon is not a black body as it returns all wavelengths toward our eye - white light. The moon is the brightest object in Tom's skyscape. However, a broader area around the moon is also bright with light! How so? 

My friend, Professor Edward Lozowski directed me to an excellent site regarding atmospheric optics which I consulted extensively. I highly recommend it as well - the site contains days of scientific discovery...  including large sections on diffraction which is the bending of light around an obstacle or through an opening. We need to fully understand diffraction to appreciate Tom Thomson's Moonlight. 

Tom Thomson: Moonlight, 1913-14, 
Purchased 1914 by the National Gallery of Canada,
 Accession Number 943 52.9 x 77.1 cm
20.8 x 30.5 inches 

Diffraction refers to various phenomena that occur when a wave encounters an obstacle. Waves can bend around a corner or through an aperture into the region of the geometrical shadow of the obstruction. The diffracting object actually becomes a secondary source of the propagating wave. Italian scientist Francesco Maria Grimaldi first used the word "diffraction" in recording his observations of the phenomenon in 1660.  A deeper investigation into diffraction reveals the particle and wave dualities of light - electromagnetic radiation. This science is extremely interesting but we do not need to go there. 

Diffraction from Small Droplets

Diffraction occurs when light is scattered or bent by small particles having physical dimensions in the same order of magnitude as the wavelength of light. An everyday illustration is the spreading of automobile headlight beams by fog or fine dust particles. A canoeist might imagine a wave on a lake diffracting and bending into the sheltered cove behind an island. 

The waves of light scattering from the surface of the particles are independent of the particle interior - which could be water, ice or even coal. The waves diffracted by the host of particles mutually interfere to give regions of enhanced bright constructive interference and dark destructive interference. The shape of the particle is even unimportant - every particle diffracts energy. 

The angle of diffraction decreases as the particle size increases. Simply, small particles bend the light more than large particles. 

The amount of diffraction also increases with increasing wavelength. Longer, red wavelengths diffract more and can tint the outer fringes of the brighter area.

Diffraction of light produces the central white disk referred to as the aureole along with the colourful interference rings of a corona. If the particles are small and uniform, colourful corona rings the aureole with blue-violet on the inside and red on the outside. These coloured rings may repeat themselves in progressively fainter shades further from the light source. If the droplets vary in size, the interference pattern is simply a bright blur. 

What the science of diffraction reveals is that Tom Thomson observed what meteorologists refer to as a aureole. The colourful rings of the corona are are absent from Tom's painting. 

Areolas and coronae are circular, despite the fact that the moon is not a full circle. The circular symmetry is produced by the diffracting particles themselves and is independent of the shape of the source of light. The brightness of both increase with the number of particles. 

Classic corona ringing the central aureole within roughly ten degrees
of the light source formed by moonlight diffracting around
small, uniform particles - diffraction pattern also called an Airy disk.

Diffraction coronae differ from haloes which are formed by refraction from comparatively large ice crystals. The roughly 10° corona is much smaller than the 22° halo which can also ring the sun and moon.

22 Degree Halo resulting from refraction of the 
moonlight within relatively large ice crystals. The cirrostratus 
is full of billions of these large ice crystals - enough so that a few 
will be oriented perfectly to refract light at 22 degrees to your eye -
thus forming the ring around the moon and alerting us to the 
approach of the warm conveyor belt and a weather system.  

PowerPoint slide from my Tom Thomson Was a Weatherman
presentation. I always used the line that the effect of the colourful
interference pattern of the corona could also be achieved using 
the Mexican beer but that the science was very different.

When I view such a phenomenon, I always use the phrase "cirrostratus coming at us" to describe a storm on the way. Cirrostratus composed of large ice crystals is more likely to be marked by the refractive, 22 degree halo. The concept of the approach of the warm conveyor belt of a weather system applies regardless whether the cloud is composed of large ice crystals or small, uniform diffractive crystals. A aureole, corona or a halo tell similar weather stories. The 10 degree aureole produced by smaller ice crystals provides longer lead time for the approaching system. 

Now for the CSI (Creative Scene Investigation)! Let’s assume that this is the evening. I believe that it is easier to stay awake in the evening than it is to get up hours before dawn.  

This summer moon is waxing - the shadowed side of the moon is on the left. In another week it will be a full moon rising in the east just as the sun sets to the west. Thus Tom is certainly looking in eastward on that summer evening probably later in the season after the biting bugs had subsided. A correlation with the eastern horizon from some shoreline should be possible given the amount of accurate detail Tom that typically put into the profile of the terrain.

There is also quite a bit of wave action indicated by the spreading out of the reflection of the moon and aureole. This wave action is more likely in the evening hours after a windy day. The planetary boundary layer is unstable during the day and the winds at the top of the boundary layer are mixed down to the surface. After a night of radiational cooling and air mass stabilization, this transfer of wind is much less likely. Of course there are always exceptions to any rule and a well-developed low pressure area nearby could produce a strong wind at any time of the day. 

The wind creating the choppy waves was likely near 10 knots and described as something between a gentle and moderate breeze in the Beaufort Scale. 

The reflection of the moon across the water is spread out by wave action. Each wave is essentially a mirror twisting and turning with the wind. With distance from the viewer, the water surface area which subtends the viewing angle increases dramatically. Countless more reflective wave mirrors can by chance direct light toward the viewer. The noticeable, bright water surface actually get larger with distance - a triangular wedge of reflected light. 

The small and uniform particles required for diffraction and the aureole, halo effect are most commonly provided by cirrostratus cloud. These high, ice crystal clouds are the advance messenger ahead of a low pressure area. The warm conveyor belt portion of the low pressure area rises higher on constant energy, isentropic surfaces. The thin, cirrostratus cloud is at the very leading edge of the warm conveyor belt. It would be cloudier to the southwest on that summer evening.

As a result, the aureole around the half-moon is advance notice of an approaching low pressure area.  Those winds rippling the Canoe Lake surface are possibly from the east and within the cold conveyor belt being drawn into the low. Tom would be looking easterly into that chilly wind.

Tom Thomson worked on this painting with the assistance of his friend A.Y. Jackson. Tom Thomson shared Studio 1 with Jackson for the first twelve months after the Studio Building was completed in January 1914. "Moonlight" was completed on Thomson's studio easel as I recreated in the accompanying image, more or less to scale. 

The Studio Building financed primarily by Lawren Harris who had a studio on the top floor. He liked to listen to music while he painted and his records could be heard blasting throughout the building. 

A.Y. Jackson in Studio 1 photographed
as he was packing up to leave for WW1

When Jackson left for World War 1 and Lawren Harris departed to be a gunnery instructor at Camp Borden, Thomson moved in to share a studio with Franklin Carmichael. When Carmichael married and left a few months later Thomson, could not afford the $22 monthly studio rental fee. Tom never really enjoyed working in the city anyway.

Tom's studio work lacks the direct interpretation, immediacy and reality that comes with the Plein Air experience. Many prefer Tom's 8.5 by 10.5 inch sketch box creations completed spontaneously while surrounded by nature. Both approaches have important parts to play in the development of of every artist on their individual journeys.

Tom's patron, Dr. MacCallum spent $176 (big money in those days) to refurbish the workmen's shed on the east side of the Studio Building. Tom  rented that shack for $1 a month. Thomson spent the summers in Algonquin Park as a guide, ranger and fire-fighter although those occupations got in the way of his plein air painting. Tom spent his last two winters Glamping in "Thomson's Shack" creating his studio master works based on his favourite plein air sketches.

"Tom did not want a studio in the building. It was altogether too pretentious for him… There was a dilapidated old shack on the back of the property… We fixed it up…and he [Tom] lived in that place as he would a cabin in the north." Lawren Harris

A.Y. Jackson apparently inherited that studio easel after Tom passed in July 1917. Tom would have liked that. 

If you paint that you see, the science of nature must be basically correct. Tom did that and these blogs attempt to explain that science, placing the art within the context that it was created. Sometimes that science is deceivingly complex. 

Thank you to my friend Professor Edward Lozowski for his guidance in constructing this post. 

Warmest regards and keep your paddle in the water,

Phil the Forecaster Chadwick

PS: For the Blog Version of my Tom Thomson catalogue raisonné, Google Search Naturally Curious "Tom Thomson Was A Weatherman - Summary As of Now" or follow this link “http://philtheforecaster.blogspot.com/2022/10/tom-thomson-was-weatherman-summary-as.html”