Most Yukoners could tell you that June 21, the summer solstice, is the longest day of the year. But probe a little deeper and it's a good bet that many of us might not be able to clearly explain why the Yukon is the land of the midnight sun. Or why summers are not blazing hot in the north.

Try the following quiz on yourself and a few of your friends:

1. Summer is the warmest season because:
    
   
   1. the earth is closer to the sun in summer
   2. the earth is tilted towards the sun
   3. both of the above
   
   
2. On summer solstice the sun is directly above:
    
   
   1. the Arctic Circle
   2. the Tropic of Capricorn
   3. the Tropic of Cancer
   4. the North Pole
   
   
3. The angle of incidence is:
    
   
   1. a solar coincidence
   2. the angle at which the sun's rays strike the earth
   3. greater in the north than in the south
   
   
4. The sun does not set over the North Pole in summer because:
    
   
   1. the Northern Hemisphere is tilted towards the sun in summer
   2. Santa needs the extra daylight hours
   3. the sun revolves around the North Pole
   
   
5. In June which of the following locations gets the most sunshine?
    
   
   1. Whitehorse
   2. Yellowknife
   3. Ellesmere Island
   
   

Solstice comes from the Latin word solstitium meaning "sun standing still." If you were standing at the North Pole on June 21, it can seem like the sun is hanging in the sky. That is because the Northern Hemisphere is tipped at its maximum angle towards the sun on this day.

"This tilt is really important to us," says Yvonne Bilan-Wallace, a meteorologist with Environment Canada based in Edmonton. "If the earth was not tilted towards the sun we would not experience changing seasons. Furthermore the temperature contrast is like a fuel in an engine, in this case a weather engine. It makes weather on this planet so interesting."

The earth is tilted at a 23½ degree angle on its axis. Without this tilt, the earth would not have distinct seasons and the North would be a far different place. The Yukon would not get such dramatic extremes in temperatures, ranging from the minus 50s in winter to the plus 30s in summer. The days would be more similar, one after another.

Interestingly enough, in another few weeks the Earth will reach its farthest point away from the sun. Our planet's path around the sun is an ellipse rather than a circle, and in January the sun is 8 million kilometres closer to the Earth than in July.

Thanks to its longer days, northern Canada receives about the same amount of solar energy in June as Florida. It would be even hotter North of 60 if not for the angle of incidence. Bilan-Wallace defines this phenomenon as "the way the sun's rays strike the top of the atmosphere."

At higher latitudes, the sun's rays strike the earth at a relatively low angle, so the North gets a weaker dose of solar energy. In June Whitehorse might receive more solar energy than the equator because of our long summer days, but it is of a lower intensity because of the angle of incidence.

She says the easiest way to see this effect is by turning on a flashlight. "Shine a flashlight directly on the table and it makes a bright circle. Shine it on the table at an angle and it lights up a larger area, but -- more important -- there is less energy on any one spot," she says.

Even with the extra energy boost we receive in summer, all locations north of 60 run a yearly deficit for solar radiation. The average annual temperature is below zero for all of the Yukon.

Bilan-Wallace says that the amount of sunlight an area receives is a function of latitude and cloud cover. "The maximum amount of sunshine in Canada is on Ellesmere Island. It has 24 hours of daylight in June and has very little cloud, so it gets about as much sunshine as Texas."

She also points out another somewhat depressing statistic. Since Yellowknife is dry and has few clouds in summer, it gets an average of 395 hours of bright sunshine in June versus 270 hours for Whitehorse. "Whitehorse gets about the same amount as Edmonton. If you want sunshine in a major northern community, go to Yellowknife," she says.

But back to the good news. On June 21, Whitehorse will bask in more than 19 hours of daylight. At the Arctic Circle and all points north, the sun will not set on the solstice. Yukoners will be out celebrating, and trying not to think about the fact that winter solstice is only six months away.

For more information on Yukon weather, contact the Yukon weather offfice at 668-6061.