Moonstruck in London

This is the spectacular sight thousands of people were treated to last night.

Hanging low in the night sky, the moon appeared extraordinarily large and glowing like a massive red ball.

Astronomers say the so-called "moon illusion" means that a full moon close to the horizon appears much larger than when it is high in the sky.

The illusion was caused partly due to the recent passing of the summer solstice, when the moon is at its lowest point in the sky and the sun at its highest. This factor was boosted by the moon being at a particular point in a

18.6-year cycle of "tilted" orbits around the Earth. The last time this happened was in 1987.

Last night the illusion was at its most spectacular but for those who missed it there is still a chance tonight although the moon will not be as impressive.

Forecasts of cloud may also affect the view but the phenomenon can still be seen for the rest of the week. A spokesman for Greenwich Observatory said they had received many inquiries over the illusion. which seemed to have fascinated people.

One theory about the moon's trick on the eye is called the "Ponzo Illusion."

In 1913, scientist Mario Ponzo said that any converging lines will appear wider the closer they are to the person looking at them, similar to staring down a railroad track.

This makes the moon on the horizon, surrounded by trees and buildings, appear larger.