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A snowboarder casts a blue-tinged shadow at Kicking Horse ski resort.

Collected Wisdom

Why's the snow blue? For the answer, look up Add to ...

It's February in Canada, so investigating a snow-related topic this week seems particularly appropriate. By the way, if you live in Toronto, snow is that white stuff that sometimes falls from the sky just before the army arrives.


"Why does a shadow on white snow have a slightly bluish tinge?" asks Mike Reiser of Cambridge, Ont. It's most noticeable in bright sunshine.


To explain this, Sjoerd Roorda of the department of physics at the University of Montreal starts with a question of his own. "First, why is snow normally white?" he writes.

"Daylight comes from the sun and the surface of the sun is white, as white as fresh snow. When sunlight enters the atmosphere," he says, "some light is scattered, the more so the shorter the wavelength. Blue is scattered more than red, which is why the sky is blue."

He explains that snow contains no pigments - it consists of tiny ice crystals and ice is transparent - but snow scatters light randomly in all directions virtually without loss.

"Therefore," he says, "it 'collects' incident light from all directions and reconstitutes the blue from the sky with the direct sunlight to make white."

However, a shadowed area on the snow misses some of the direct light and scatters only the light falling indirectly (the blue from the sky). And that, he says, is why a shadow appears bluish.

Dr. Roorda concludes: "Light can also be separated into its constituent colours by refraction (in a rainbow or a prism), as was famously done by Isaac Newton, who also reconstituted white light by recombining the spectrum, thus demonstrating that all the colours were already present in the incident white light."


Brenda Lawrence of Manilla, Ont., asks: Does a sword really make a "shing" sound when it is drawn from its scabbard, the way it does in the movies?


It can, says Scott Moyle of Toronto.

"The piece of the scabbard nearest the opening is called the throat," he writes, "and it's usually a shaped piece of metal designed to accommodate the blade at its widest point. When a sword makes a 'shing' sound, it's from the blade grazing against the throat on its way out."

However, he says, most scabbards aren't deliberately designed to do that because contact with the throat damages the blade's edge.

He adds that he owns a stage dagger with sprung steel panels mounted inside the scabbard's throat.

"It makes a terrific theatrical sound when drawn, but I highly doubt any historical scabbard would be built that way."

In short, he says, swords will occasionally "shing" in real life by chance but very rarely by design. "In movies, they always do, because it sounds cool."


Why do some sports have an umpire while others have a referee? Arthur Powell of Smiths Falls, Ont., would like to know.

Colleen McCarthy of Halifax recently heard an interview with Canadian yachtsman Derek Hatfield, who is competing in the single-handed, around-the-world race known as the Velux 5 Oceans. She wonders how solo sailors manage to get any sleep.

Campbell McLeish of Terra Cotta, Ont., wonders: "Is it more energy-efficient to maintain your thermostat setting at a constant temperature 24/7 during the winter at, say, 20 degrees, or to lower it to 18 degrees when you go to bed, but then have to heat up the house each morning back to 20?"

Send answers and questions to wisdom@globeandmail.com. Please include your name, location and a daytime phone number.


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