LONDON — The moon darkened, reddened, and turned shades of gray and orange Saturday night during the first total lunar eclipse in nearly three years, thrilling stargazers and astronomers around the world.

The Earth’s shadow took over six hours to crawl across the moon’s surface, eating it into a crescent shape before engulfing it completely in a spectacle at least partly visible on every continent.

About a dozen amateur astronomers braved the cold and mud outside the Croydon Observatory in southeast London to watch the start of the eclipse.

“It’s starting to go!” said Alex Gikas, 8, a Cub Scout who was studying for his astronomy badge. “I’ve never seen anything like it before. I’m really excited.”

By the time of greatest eclipse, shortly after 5:44 p.m. EST, the light of the full moon was replaced by near-total obscurity.

“It was really very dark,” said Paul Harper, Chairman of the Croydon Astronomical Society, who estimated that the moon had lost over four-fifths of its luminosity. “It was quite a nice one.”

Lunar eclipses occur when Earth passes between the sun and the moon, an uncommon event because the moon spends most of its time either above or below the plane of Earth’s orbit.

Sunlight still reaches the moon during total eclipses, but it is refracted through Earth’s atmosphere, bathing the moon in an eerie crimson light.

Mike Ealay, a 60-year-old architect who wandered over to the observatory to watch the eclipse, said the red color of the moon made it look like a close-up version of Mars.

“I think it’s quite exciting. It’s like having the red planet on your doorstep,” he said.

Despite cloudy conditions over much of Europe, a variety of Webcasts carried the event live, and astronomers urged the public not to miss out on the spectacle.

“It’s not an event that has any scientific value, but it’s something everybody can enjoy,” said Robert Massey, of Britain’s Royal Astronomical Society.

The moon’s red blush faded as it began moving out of Earth’s shadow just after 8 p.m. EST. The eclipse ended a little more than hour later.

Residents of east Asia saw the eclipse cut short by moonset, while those in the eastern parts of North and South America had the moon already partially or totally eclipsed by the time it rose over the horizon in the evening.

While eastern Australia, Alaska and New Zealand missed Saturday’s show, they will have front row seats to the next total lunar eclipse, on Aug. 28.

On the Net:

NASA Lunar Eclipse Page: sunearth.gsfc.nasa.gov/eclipse/lunar.html