Nature's greatest show on Earth

The winter season is a dead time on the Hurtigrute, the famous coastal voyage along the rutted Norwegian coast. The ships that run between Bergen in the south and Kirkenes near the Russian border transport cargo and a handful of passengers from one small port to the next, battling against gales, temperatures as low as -30C and constant darkness alleviated by only a few hours of twilight at midday. But in summer, when the magnificent coastline is illuminated around the clock by the midnight sun, the Hurtigrute becomes a popular tourist route. Yet these fair-weather travellers miss out on the Northern Lights, a glimpse of which is worth a month of the midnight sun.

The winter season is a dead time on the Hurtigrute, the famous coastal voyage along the rutted Norwegian coast. The ships that run between Bergen in the south and Kirkenes near the Russian border transport cargo and a handful of passengers from one small port to the next, battling against gales, temperatures as low as -30C and constant darkness alleviated by only a few hours of twilight at midday. But in summer, when the magnificent coastline is illuminated around the clock by the midnight sun, the Hurtigrute becomes a popular tourist route. Yet these fair-weather travellers miss out on the Northern Lights, a glimpse of which is worth a month of the midnight sun.

Northern Norway is one of the best places on Earth to look for the aurora borealis, a fact not lost on the Norwegian Coastal Voyage Company, which has introduced The Northern Lights Voyage - a four-day cruise from Northern Norway to Bergen, which affords a brief opportunity to view the aurora from the comfort of the ship. Bad weather, clouds, a lack of activity on the sun, even bright moonlight can obscure it, so I boarded the Richard With at midnight in Tromso with few expectations.

The Lights had appeared over the small Arctic town earlier that evening but were gone by the time we arrived and the four people booked on the cruise with me were too tired to sit freezing on deck in case they returned - which they rarely do after midnight. As the ship continued its journey southward the clouds cleared and the aurora spread its glory across the night skies, witnessed only by the crew.

The following morning blue-black mountains, crusted with ice and snow, loomed out of the half-light of the morning. The sun should have risen above the mountains for two hours around midday but thin cloud kept it hidden. The ship had fewer than 70 passengers out of a possible 671 and only a handful of those ventured into the numerous viewing lounges or on deck. "Danger of Life!" was written on a yellow sign warning passengers not to fall off Deck 5 into the icy waters below, but there seemed little danger of much life around here. Nothing moved to distract the eye - no birds, no fish broke the millpond surface of the water, the seals had left their rocks and the sky was devoid of aeroplanes.

Here at the most northerly tip of Europe, with only a narrow strip of islands separating the ship from the polar seas, life seemed to have succumbed to the cold. The hypnotic effect of the stillness and silence was delicious, like standing in the desert, rendering daily life comfortingly insignificant. It was time to admire the Lofoten Islands through which the ship was sailing although twilight dimmed to night by 4:30pm - to the dismay of a couple who had not realised that much of the cruise would pass in darkness. We left the island-sheltered waters for the open sea after dinner and the ship pitched and rolled. Clouds obscured the stars, making it unlikely that the Lights would appear again that night. The bar served expensive beer and wine that we sipped very slowly to help the time pass as we rattled around the seven decks.

Before seasickness forced me to retire to my bunk, I braved one last trip on to the wind-blasted deck. The night was coming to life. Clouds to starboard had cleared and a streak of luminescent green appeared in the darkness. Gradually it moved across the sky like a gauze curtain in a breeze. Rays of emerald light shot towards us like spears of the Valkyries, messengers from Valhalla, whom Vikings believed appeared as aurora to point out warriors who would die in battle. The Sami, indigenous reindeer herders of northern Europe, believe the Lights to be unhappy spirits trapped between Earth and Heaven, waiting to sweep down and decapitate anyone attracting their attention. Children are told not to wave white handkerchiefs or whistle while the Lights play overhead.

The cause of the Northern Lights was a mystery first considered by Greek philosophers in the 6th century BC. Not until 1900 was the enigma solved, by a Norwegian physicist of great but unrecognised brilliance, Kristian Birkeland. He was so far ahead of his time that his contemporaries could not believe this diminutive professor from a small and insular country could possibly have solved the riddle that perplexed the greatest natural philosophers for three millennia. Birkeland suggested that aurorae formed when electrically charged particles from the Sun were channelled towards the poles of the Earth by the planet's magnetic field, creating the Lights as they hit the atmosphere.

This year and next are particularly good times to look for the Lights because the Sun, which has an 11-year cycle, is in its most active phase, emitting more of the charged particles that cause aurorae.

The second day of the cruise began with a brief announcement that we were crossing the Arctic Circle. Someone asked whether the line could be seen at sea as well as on land. I assumed they were joking. The ship made brief stops at several of the islands en route but the ports all looked the same and we left the ship only to stretch our legs. The day was punctuated with large, tasty meals and by evening we were nearly 150 miles south of Tromso, where the aurora is rarely seen.

Seeking air before dinner, I ventured on deck at 6pm and watched in amazement as two parallel arcs of bright, pale-green light spread silently across the northern horizon, swaying together over thousands of miles of space like a corps de ballet. It was rare to see the Lights from so far south and even the talents of the Norwegian band employed for our entertainment were not sufficient to drag us away.

As we cruised south, the crust of the Earth seemed to thaw under the influence of the low-lying Sun. Fish eagles swooped over the fjords and more villages could be seen speckling the strips of flat land at the foot of the mountains. We docked at Trondheim in the early morning of the third day and had a couple of hours to explore the ice-covered canals, narrow streets of wooden houses and broad avenues of elegant stone buildings radiating from the central square. In the crisp, early morning, Scandinavia's largest medieval building, the Nidaros Cathedral, loomed magnificently over its frosty surroundings, bristling with copper-covered spires. The museums, churches and shops were closed at that hour, a reminder that the "cruise" follows the needs of the Hurtigrute schedule, not the tourists, but the atmosphere compensated for missed cultural excursions.

As we neared Bergen on the final day the clouds rolled in, obscured the view and brought rain and sleet. It always rains in Bergen so we had a typical taste of this city, lovely despite its climate. Bryggen, the old quarter to the north of the old harbour, is a jumble of 18th-century warehouses, wooden merchants' quarters, old churches and cafés in which to take refuge. Here, too, is the start of the dramatic funicular ride to the top of a mountain from which we could see Bergen nestling in the fjord below and the Richard With preparing to travel north again, to the land of the aurora borealis.

* Lucy Jago is author of 'The Northern Lights: how one man sacrificed love, happiness and sanity to unlock the secrets of space', to be published in May by Hamish Hamilton (£14.99).