Tom Thomson's “A Northern Lake" Was the Belt of Venus Sunrise

There are many entries in the Tom Thomson catalogue with the word “lake” employed. “Northern” is often used in conjunction as well. A classic example is “A Northern Lake” in the Art Gallery of Ontario collection. The painting was apparently created in 1911, 1915, or maybe 1916 depending on who you listen to. The  "TT Estate Stamp" appears prominently in the lower left corner so Tom didn't bother to sign this work either. I will leave the actual creation date for this observation to the experts. I wish to focus on “what” and “why” because I feel that the name totally misses the point of Tom's sketch. 

"A Northern Lake" circa 1916; W26.7 x H21.6 cm (overall)
10.5 x 8.5 inches - sketch box size
oil on composite wood-pulp board
 Gift from the Reuben and Kate Leonard Canadian Fund, 1927

This is a skyscape with the horizon at the lower third of the sketch box panel. There is indeed a lake in the foreground and what appears to be some ice along the shoreline. There was no foliage on the trees. Tom certainly painted this to record the rose and pink colours in the sky but what was he looking at?

There are just two viable options. 

• One is the rose colour resulting from front-lit cloud with the sun on his back. The soft and diffuse edges of the altostratus or cirrostratus cloud could explain what Tom was trying to capture with his oils. 
• The other is that Tom was looking at the eclipse of the atmosphere by the shadow of the earth - the Belt of Venus (associated with the Greek goddess Aphrodite and Roman goddess Venus - not the second planet in the Solar System). 

A backlit cloud is not an option given the strong colours of the lake and marsh and even the distant hills. Tom’s subjects were clearly not in strong shadow. (See graphic explanation below)

Everyone sees this phenomenon twice a day but rarely ever takes any notice. Perhaps the best way to decipher Tom’s motivation is with some actual images. 

Singleton October Sunrise with Arctic Sea Smoke rising from 
the lake. The skies were clear overnight and the temperatures
plummeted. No more swimming for me... The dark grey
on the horizon looks like altostratus coming at us...
but it was the shadow of the earth on the lower atmosphere -
the Belt of Venus was the pink above that. 

The same scene twenty minutes later with only fog in the sky.
The grey horizon disappeared as the sun continued to rise.
The grey was not clouds at all. .

The earth casts a shadow on the lower atmosphere twice a day at your location: the first at sunrise if you gaze toward the west and the other at sunset looking toward the east. The shadow in the sky lasts only about 15 minutes - just long enough to boldly observe and lay the oils on a sketch. This phenomenon is referred to as the “Belt Of Venus” and that is the what and why of Tom's sketch. 

The Belt of Venus, also called Venus's Girdle or the anti-twilight arch is an atmospheric phenomenon visible shortly before the sun rises or after sunset, during civil twilight (the geometric center of the sun is within 6 degrees below the horizon). The pinkish glow surrounds the observer and extends 10 to 20 degrees above the horizon.

Any graphic to adequately explain this phenomenon must be greatly distorted.  

• Remember that the atmosphere is actually quite thin similar to the skin of an apple. The troposphere where almost all weather occurs extends only 8 to 14.5 kilometers high (5 to 9 miles). This part of the atmosphere is dense and thus the most likely to scatter light creating the visual effects that we enjoy. 

• Also, recall that the sun is far from the earth at about 8.3 light-minutes away. On average, the earth is 150 million kilometers away from the sun.

• The earth is only 12,742 km in diameter. The dimensions of the earth are dwarfed by the distances involved. 

As a result, the following graphics are extremely distorted.

The following graphic explains the optics of the Belt of Venus. 

1. Observer's line of sight away from the sun.
2. The sun is within 6 degrees below the observer's line of sight toward the sun.
3. Light from the sun passes through a very long atmospheric path. Short wavelengths are scattered out of the sun's beam leaving only longer red waves of light.
4. The observer sees reddish light backscattered from the illuminated atmosphere.
5. This is the shadow of the earth and this portion of the atmosphere is not illuminated by the direct beam (refraction and diffraction can get light into this region but let's keep this simple)

“A Northern Lake” Diagnosed

Perhaps an image that was taken by my friend George Kourounis, RCGS Explorer In Residence, Nat Geo explorer, & TEDx speaker will help. George was on a sunrise balloon ride in Türkiye facing west just before the sun rose up from behind him. The Earth itself gets in the way of the sunlight and casts a shadow on the lower atmosphere. The pinkish shade above the shadow is the Belt of Venus. 

Image looking west at sunrise by George Kourounis,
RCGS Explorer In Residence, with permission

Tom painted the Belt of Venus most likely at sunrise on a chilly morning. He was a morning person much like me. His subject was the sky. 

I must confess that a very similar and equally convincing argument can be made that the pinkish area in Tom's sketch is actually sunrise, front-lit cirrostratus, or altostratus associated with a warm conveyor belt approaching from the west. 

The sharp and dark horizontal line on the lower horizon would be the nimbostratus deformation zone that I have mentioned so many times. Rain could be on the way. 

I cannot be absolutely certain. I was not there painting with Tom as much as I would have loved to be. It is important to keep an open mind and that is how we learn - even from our mistakes. 

Warmest regards and keep your paddle in the water,

Phil the Forecaster Chadwick

PS: I wish to also explain why a backlit scene is not an option due to the strong colours that Tom included in his foreground. Here is the explained sunset from the October day when this Blog was posted. The skies were clear and this image was taken minutes after the sun set below the western horizon of Singleton Lake. 

Backlit Scene Looking West toward the Sunset Sky

PSS: Here is an image from October 2022 showing sunrise altostratus on the western horizon. The cloud was front-lit but if I had taken the picture earlier than 7:30 am, it might have been confused with the Belt of Venus. I missed that opportunity but I was close...  

7:30 am Saturday, October 15th, 2022

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”