Whatever their theory, Picton residents have been noticing strange lights in the sky in recent weeks, with people reporting spectacular, multicoloured lights dancing above the horizon to the west.

The phenomenon has a scientific explanation that's a little more mundane, said David Turner, a local member of the Royal Astronomical Society.

"It's the planet Venus," he said.

"It's an optical illusion - when Venus gets near the horizon it seems to change colour and jump around."

The illusion occurs as a result of heat rising off the Earth's surface, and is more marked after a hot, sunny day.

When Venus gets near the horizon, which currently happens in Marlborough at around 10pm, its light passes through a lot more of that heated atmosphere, causing the often spectacular effects.

"It's the same as the effect you get with heat rising on a hot tin roof," Mr Turner said.

Similar atmospheric disturbances cause the twinkling of the stars, he explained.

"Venus is the very bright planet that you'll see over to the west," he added.

"It's covered in white cloud that reflects all the sunlight, which is why it appears so bright.

Venus goes through phases like the moon, but this optical illusion happens all the time - and it's not just in Picton.

It's just that people seem to notice it more sometimes.

"The Astronomical Society often gets calls about these planets near the horizon.

"It happens with Jupiter as well."