The day began exactly as it did on that fateful date 10 years ago: under a crystal-clear sky that heightened the colours of the city and made the surrounding skyscrapers sparkle.

The smoke from its exhaust was a greasy black smudge in the distance, against the crystal-clear Hawaiian sky.

It had rained earlier, washing the city of daytime soot and grime, leaving a perfect crystal-clear sky dotted with thousands of stars.

A fire was out of the question here: its smoke would clearly be seen in the crystal-clear blue skies from both the air base and the army base, nearly five miles away.

Then they watched him level his bird in the crystal-clear sky, skirt the rim of Valhalla glacier, and vanish over the crooked spine of mountains running toward the coast.

He scanned the crystal-clear sky.

But the real thrill came as they approached New York in crystal-clear skies.

During the South Pole summer - November to mid-February - the station is thronged with 170 or so scientists, including many astronomers who are drawn by the crystal-clear skies.

And they watched as it obliterated the incoming empty aircraft in dark but crystal-clear skies more than 20 miles from where they stood.

But crystal-clear blue skies enhanced the beauty of the ice-capped mountains and the fiord wrapped in sea ice.