It's evening in the vast Chihuahua desert, ten miles east of Marfa, Texas.

I'm sitting on a wall with Joe from Colorado, a trio of polite bikers and a bunch of beery students. We are all staring into the blackness south of Highway 90, looking for the 'Marfa Mystery Lights'.

For maybe 50 years, visitors to this area have reported peculiar light phenomena - small gyrating orbs on the far horizon. The lights usually appear at night.

Various explanations have been offered. Some blame car headlamps on highway 67, refracted by the layered air of this high-altitude desert. Others blame reflections from rock, electrical discharge or the ghosts of gold-digging Spaniards.

That Marfa should boast a mysterious phenomenon is fitting. This is one of the oddest small towns in America.

The town's strange name comes from a Dostoevsky novel. It is also impossibly remote - 200 miles from anywhere.

Marfa's main business, apart from light phenomena, is equally off-beat. This is a world centre of modern and minimalist art. Forty miles out of town, for instance, a complete Prada shoe shop has been erected on the side of the desert highway, featuring the 2005 Fall collection. The shop is a laugh-out-loud art installation.

In Marfa itself the galleries are everywhere. Biggest of all is the Chinati, a disused garrison converted into a sculpture park. Visiting this place, with its Donald Judd steel boxes and Dan Flavin neon shows amid the cactus and jackrabbits, is like finding the Tate Gallery on a glacier.

But what about that real mystery - the desert lights? Will we see them tonight?

Straining my eyes, all I can honestly see is a parade of car headlamps, twinkling in the ebbing heat of the desert dusk.

Then someone points.

A small green light to our left, which has hitherto been stationary- and dismissed as a ranch-light - seems to move. It shifts left, then right.

It's too far away to be photographed, but nonetheless everyone is excited. Joe from Colorado is actually standing on his picnic chair.

For several more minutes the light wobbles. Then it stops.

Still, I'm not sure what I've seen. Maybe some piezoelectronics. Maybe a hovering helicopter. Perhaps I have been part of a mass hallucination?

The next day I go back and have another look, by day.

Turns out the green light belongs to a ranch - the glow must have been refracted light from a porch lamp.

Disappointed, I head back to the car.

And it's then that I see something really weird - a ripple of light across the distant mesa. It's momentary.

It's truly startling. And then it's gone.

I have no idea what it was, but it certainly wasn't a car. The hairs on my neck are prickling.

No wonder they call them spooklights.