Page 108 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

An aurora is an amazing natural
phenomenon caused by the solar
wind and Earth’s magnetosphere

AMAZING

AURORAE

DISCOVER Above the northern horizon a green arc melts into much better chance of seeing all this activity in far
HOW THESE view. As you watch, red and green rays begin to northern or southern latitudes.
emanate from it. These grow into long weaving
Earth’s magnetic fi eld is similar to the fi eld from
BEAUTIFUL ripples that stretch like ribbons across the entire the north and south poles of a bar magnet. This
CURTAINS OF sky, almost as if they were blowing in the wind. means that there will be the same activity at each
pole – any aurora happening around the north pole
You are witnessing one of the true marvels of the
LIGHT ARE natural world: an aurora. will also be happening almost identically around
FORMED The phenomenon is caused by charged particles the south pole.
streaming out of the Sun and interacting with
Earth’s magnetic fi eld – our planet’s protective NORTH VS SOUTH
shield – which channels them down towards the Aurorae are easier to see in the northern
‘magnetic’ poles. As the particles reach lower hemisphere, for various reasons. Norway, for
altitudes, usually between 80 and 200km, they hit example, is inhabited along the coast because of
and excite the the gases in Earth’s atmosphere, the warm Gulf Stream. This makes it easier to get
causing a distinctive and colourful glow. closer to the action – a cruise can take you into
The magnetic poles are about 11° away from the aurora country. In the southern hemisphere, the
geographical poles (the ones traditionally refered aurora sits over Antarctica, which is not an easy
to as the North and South Poles). So you stand a place to get to. From this frozen continent there
108 skyatnightmagazine.com 2012