What might you see on a Hurtigruten astronomy tour along the coast of Norway? Every voyage is different, but I'm going to describe sky-watching highlights of the astronomy tour that took place in autumn 2012 on MS Finnmarken.

The full Moon
The big attraction is the aurora borealis – the northern lights – so people want the best conditions to see them. An aurora is so insubstantial that you can see stars through it, so the usual advice is to avoid a full Moon. With the Moon full or gibbous for the first week of our trip, people were apprehensive.

But although a bright Moon would overwhelm a weak aurora, Finnmarken was headed into the Arctic Circle. The northern lights should be strong under the auroral oval (a region of permanent auroral activity) and beyond the glow of city lights.

Stargazing
As the ship sailed north from Bergen, the weather was superb: sunny days, clear nights, calm seas and mild temperatures. There was no auroral activity the first few nights, but astronomer Ian Ridpath led stargazing on deck.

The Moon did wash out faint objects in the sky, such as the Milky Way. However it’s the brighter stars that largely define the constellations, so it was easier to find and recognize them. One of Ian's talks was “The Stories of the Stars” and on deck he pointed out constellations from his talk, including those of the great Perseus and Andromeda myth.

The so-called Summer Triangle of Vega, Altair and Deneb was easy to find, even at the end of October. (It really needs a new name!) We found Polaris, known to the Vikings as Leidarstjarna (Guiding Star), and it did seem to lead us northwards.

The Moon was in the constellation Taurus near a brilliant Jupiter and reddish Aldebaran, the brightest star of Taurus. Also in Taurus are the Pleiades – or Seven Sisters. Although they're part of a distant star cluster of around a thousand stars, most people can't see more than six without binoculars.

Aurora or cloud?
We can’t see color in very dim light, so the vividly-colored aurorae in photos tend to look grey to the human eye. The colors are there, so if you set your camera for a longer exposure, it collects enough light for them to show up. This is a good way to find out whether the nebulous patch on the horizon is a cloud or an aurora. A digital camera will show the green of an aurora.

In a fairly clear sky an auroral arc is very distinctive. In fact, it may arch all the way across the sky. Instead of an arch, you might get an irregular band, sometimes with perpendicular rays giving it a curtain-like appearance. If the aurora is directly overhead, the rays seem to radiate like a stellar crown, so it’s called a corona.

We saw the light
You can see colors in a strong aurora. On Halloween night sky-watchers benefited from a flurry of solar particles hitting the Earth's magnetic field. This triggered aurorae all around the Arctic Circle. We saw a display that varied between a creamy color and a pale - but noticeable - green. Some photographs even showed a bit of red.

The shapes and movement were on a grand scale. At the peak of the display there were soaring columns and magnificent bands all around the sky. The full Moon illuminated the snow-frosted mountains and made the whole scene magical. One of my favorite moments was seeing an auroral band rising above a mountain peak like a cold volcano.

Bright Moon, city lights
In the city of Tromsø the astronomy group visited the Northern Lights Planetarium. When we came out, even though it wasn’t fully dark, and despite the city lights, auroral activity was strong and filled the sky.

Awe-inspiring
The word “awesome” is debased by its common and exaggerated overuse, but the grandeur and exquisite beauty of what we saw that night did excite awe and amazement.

One tableau stands out in my memory. The three bright celestial objects in Taurus — Jupiter, the Moon and Aldebaran — were all in a line. Auroral shapes were forming and expanding across the sky around them, including one that seemed to circle and frame them.

As we watched the scene unfold, a fireball soared across the sky. A fireball is an exceptionally bright meteor. I usually find that a meteor is gone by the time I turn my head after someone has shouted “Look!” Our brilliant meteor crossed the sky in a comparatively stately manner, leaving a glowing trail behind.

But the most wonderful sight of all was an aurora that looked like a vast shimmering drapery of green and red. The colors were clearly visible and the changes swept across it as if it were being blown by a celestial wind.

Whether they had seen aurorae before or whether the voyage was the realization of a long-standing dream, it was a memorable night for everyone. It is truly awe-inspiring to see the northern lights dancing in the sky over snowy mountains and moonlit fjords.

This is the second part of a two-part article.

Note: I took part in this tour as a lecturer and assistant.