Latest/earliest months to view Northern Lights?

Look - NL are there all year.
But only if solar activity is high. Solar activity is determined by the sun - not by being in one country or another.
Solar activity is low these years.
NL are most common somewhere around and somewhat north of the Polar circle.
Take a look here: http://www.swpc.noaa.gov/pmap/pmapN.html and here http://www.gi.alaska.edu/aurora_predict/worldmap8.html

In addition to Solar activity and right latitude you need 2 more thing:
Darkness and clear skies.
Darkness means that anytime between 22 Sept and 22.. March you have 12 hours or more between sunset and sunrise - means 10 or more hours for observation - in the other half the hours of observation falls - further north = worse.

Location - except for latitude is ONLY interesting in relation to weather (and entertaining a 7yr) - (who won't be interested in NL - it is not THAT spectacular - in a kids mind),

Weather is unpredictable all over up north, but any west facing coast is worst (Iceland, Norway) - while chances in inland - ON AVERAGE - are better: i.e. n.coast of Iceland, Norway far up north (where the coast is north facing or you can go inland) + Svalbard - but first of all Finland and Sweden, if we limit to Nordic countries. Iceland is a bit in the south end of the range. Greenland has the same "coastal problems" as the other places, although chances at the main airport at Kangerlussuak are great.

You cannot count on anything even remotely like a guarantee ANYTIME - even if you are on location for 1 week and observe any clear night (if there are any) - on another vist it may be more or less continuos for 10s of hours.
Only 100% guarantee is to live up there - out on the countryside (only powerful NL can be seen in towns due to "light pollution") and to be outdoor very often.

It would be mid March and mid Sept.
B-)

If you are just sufficiently far south to get true darkness in midsummer night, you can in principle see the Northern Lights all year. This website gives details. http://www.gedds.alaska.edu/AuroraForecast/ But that far south, it has to be a very strong aurora in order to be seen at all, at any time of year. My grandfather once saw them while on summer holiday in Norfolk, England. But there was much less light pollution in the 1930s.

I got up one August morning in northern Iceland in late August to be told that the Northern Lights had been visible the previous night. You get a short period of true night by then. But she saw them about 1am and I, like most people, missed them because we were all asleep. By computation of the number of days the other side of 21 June, we can compute that the latest they can be seen in spring is about mid-April. But going to Iceland and hoping to see the aurora at those times of year, indeed any time of year, but especially those times, is like buying a lottery ticket because you hope to win the lottery. And are you really going to be sitting up at 1am in faint hope?

You should be aware that the strength/frequency of the aurora follows the 11-year sun-spot cycle, which is currently close to its minimum. You'll have a much better chance of seeing good auroras in 3 years or so.

Thank you to everyone for your replies and explanations. Will give the NL a miss. Might still go to Iceland to look at its other wonders.

Cheers.

I saw northern lights in the Mývatn area in Iceland during mid April. Pictures.
A 7 year old kid might be too impatient and not really understand the fact that you can spend hours waiting and hoping and for nothing to happen...

I was very lucky I guess... someone had warned me that if you see white smears in the daytime, it might be a prelude to NL. So I was very alert that day and evening. When I saw something funny from the window of my guesthouse (about 23.30h) I took my camera, warm coat and hat, and walked as far as I could from the lights of the town, and then indeed there was a display of northern lights going on, lasting for about half an hour. I was very moved and it also felt like my eyes were playing tricks on me.
Icelanders will probably be best at predicting whether there is a chance that evening and at what time.

Iceland is amazing, one of the most beautiful places I've ever seen on the planet and I've travelled quite a bit. Tips on my website.

Hi Cecilia,

Just looked at your lovely trip pictures. I am currently researching for a possible 3 or 4 day city break to Reykjavik in April. Just need to find out if it is easy and cheaper to go to the sights covered by the Golden Circle route on public transport or join one of those coach tours as we won't be hiring a car.

Thanks for sharing your info.

Hi Kawan2,

Nice to hear you liked my pictures.
I suppose there are public buses to the Blue Lagoon. Not so sure about Thingvellir national park and Geysir and Gulfoss though - I mean, as far as the guidebooks told me there might be only one or two per DAY!
I think you will need to go with a tour.
Or reconsider and rent a car after all. I was happy with my deal through Sixt.com, and loved having the freedom and time. I think your young son will have a blast at Geysir (the Strokkur geyser goes off around every ten minutes), so you might want to have the freedom to stay there for a while. The good thing about April is that it doesn't get very crowded so you can stand close and see it well. (I saw pictures of Strokkur in July with multiple rows of people around it.)

Your son may also enjoy the Vulcano Show, a somewhat messy movie made by a Danish guy, it's shows every day in a special cinema in Reykjavik. The movie itself is a bit weird without any real order or logic, but the images of volcanos, lava, glaciers melting because of vulcanoes underneath and causing major floods, a whole new island coming into existence at the coast... are amazing.

Have fun, Iceland is beautiful!
Cécile