In the second part of our Northern Lights blog series, Dr. Robin Catchpole reveals the best time and place to see the Aurora Borealis.
When and where is best to see the Aurora Borealis (Northern Lights)?
On two hundred or more nights a year there will be some activity inside the auroral oval. This is a broad ring of sky cantered on the Earth’s magnetic pole, which lies in North Canada and does not coincide with the Earth’s rotation axis. In Norway the outer edge of the oval more or less coincides with the Arctic Circle. Activity is seen predominantly on the side of the oval opposite the Sun, in other words from maybe ten in the evening until the early hours of the morning.
Because activity takes place between 60 and 1000km above us, it means that the Aurora can be seen outside the oval, towards the north.
Even on a night with auroral activity there can be quite long periods of time when nothing is visible, followed by ten or more minutes of intense activity. Ideally stay up all night, otherwise from 10pm to 3 am, or more realistically watch the sky for at least two hours.
Image taken from last year’s Arctic Explorer tour, courtesy of Dr Robin Catchpole
It is only possible to see the aurora during winter months from October to the end of March. Outside this time the sky does not get dark enough at night.
The aurora can be seen at full moon, as we did in January 2015. Many people think this is the best time to take pictures, with the surrounding country and trees visible, giving a sense of place and scale.
Occasionally, perhaps a few times a year, there will be a spectacular Aurora that extends far south of the auroral oval and aurora have been seen as far south as the Caribbean. These displays are caused by out-bursts or ‘coronal mass ejections’ (CME) from the surface of the Sun, when millions of tons of the Sun’s atmosphere is hurled into space.
Aurora predictions and real time reports, can be found at; http://www.spaceweatherlive.com
Aurora and the Sun
The surface of the Sun is threaded by magnetic fields. Where these concentrate and break through the surface, they prevent convection, making a small patch of the Sun, cooler and darker, which we call a sunspot.
Associated with sunspots, arches of magnetic field writhe above the Sun’s surface creating solar flares as they split and connect, they can launch material from the surface of the Sun into space. These clouds of plasma, weighing millions of tons, called ‘coronal mass ejections’, splay out from the Sun into space in curved paths like water from a spinning rose. It is not immediately obvious if a patch of plasma is going to collide with the Earth. But if it does and the magnetic field of the plasma couples with the Earth’s field, it buffets the Earth’s field and some of the plasma leaks down the Earth’s magnetic field and can cause dramatic aurora, visible way beyond the magnetic oval.
The number of sunspots and dramatic coronal mass ejections follow an approximately 11 year cycle. The current solar cycle reached an initial maximum at the end of 2011 and a broader maximum at the beginning of 2014. But this does not mean that aurora can only be seen at solar maximum.
Read Part 3 of Robin’s blog – How to photograph the Aurora Borealis?
This blog post was written by astronomer and researcher Dr. Robin Catchpole, who recently hosted our Arctic Explorer adventure as a guest astronomer.