Ask Mr. Brain

Why are birds' feathers asymmetrical? Asymmetrical flight feathers act like individual wind foils, giving the bird better lift in flight.

It seems from fossil records that feathers have been asymmetrical since the earliest birds took to the air.

Birds have incorporated the wind foil design on two levels.

First, their wings resemble the wings of an aeroplane, slightly convex above and concave below, with a rounded edge facing forward, and a longer, tapering shape on the trailing side.

This shape provides aerodynamic lift for flight.

Birds also get lift from their individual flight feathers, and on a flight feather, you will notice that one side is smaller than the other. On that side, the flexible 'barbs' that make up the feather's surface are shorter and a bit stiffer.

Stiffness is necessary in the leading edge of a good wind foil, and that shorter, stiffer side of the feather serves as the leading edge when the bird flies.

Just as the bird's whole wing resembles an aeroplane wing in cross section, so does each individual flight feather, with a stiffer edge facing forward, and a longer trailing side.

Feathers have other adaptations for flight, such as the interlocking hooks called barbules that act like velcro to keep the barbs zipped together, forming an unbroken surface.

What are green icebergs? Green icebergs have fascinated mariners for hundreds of years and puzzled scientists for at least 60. After all, icebergs should be blue.

On November 19, 1988, the accumulated curiosity of all those years became too much for two Seattle scientists.

Distracted from their official responsibilities on an Australian research expedition, Stephen Warren and Richard Brandt scurried on to a green iceberg that had grounded near Australia's Mawson Station.

Once on the iceberg, Warren and Brandt examined its spectral properties. Then they toted a chunk of it back to their University of Washington lab in an ice-packed suitcase.

In the lab, they tested the chemical and physical properties of the green iceberg chunk and other samples of water and ice taken nearby.

The analyses helped Warren, Brandt and four colleagues piece together the unlikely series of events that produces a green iceberg.

First, sea water that's rich in organic matter has to freeze to the bottom of an ice shelf. The organic matter absorbs blue light, shifting the colour of the water from blue to green.

Essentially the sea water is green, and when it freezes to make ice, the ice is green.

Then that green ice has to get pushed to the edge of the ice sheet without melting.

Finally, the ice has to break into small pieces that can capsize. That is because the ice on the top of the ice sheet comes from ordinary snow, which makes plain old blue ice.

If the iceberg does not capsize, that is all anybody will ever see.