Fox Fires 1: Introduction and Terms
Aurora borealis – just hearing those words make me look outside and check for clear skies. The mystic dance of the lights are a big part of my life. I hope this guide can help to answer your questions.
Different tales and stories about auroras have one thing in common: there is magic seeing the lights in the sky. A tale from the Sami people says that a fox is running across the fells of Lapland and its tail whirls up snow high in the air. So it is not hard to understand why the Finnish word for Aurora Borealis is revontulet (fox fires). Being outdoors at night in complete silence and solitary, I sometimes wonder if I will ever be lucky enough to see that fox..
This guide consists of five parts and the goal are to help
– to understand terms which are commonly used
– to have realistic expectations
– to know when and where to go and what to bring
– to capture some decent aurora photos
– provide you with a list of useful links.
After reading through this guide, you will understand that auroras cannot be predicted perfectly. Certain places and nights may prove to have higher viewing probabilities, but there is no guarantee to see auroras in any certain colors at any certain time in any certain place.
For me, all these uncertainties make it even more special when seeing Northern lights. Every night is a surprise, you just never know what to expect.
Here is a list of the most common terms used in connection with auroras. It is not my goal to write perfect, scientific explanations, but to make these terms understandable to everyone with some examples.
A display of light in the night sky of the Northern hemisphere. It is caused by charged particles from the sun. When large numbers of these particles break through the magnetic field of Earth, they collide with atoms in our atmosphere and create light in certain colors. Think of a rainbow. The sunlight hits countless raindrops producing a colorful rainbow.
The name Aurora Borealis comes from the words Aurora (the Roman goddess of dawn) and boreal (the Greek name for north wind). Auroras (or more correctly aurorae) in the Southern hemisphere are called Aurora australis.
an oval-shaped area around the magnetic poles, in which auroras might be visible. Imagine you open the tap on your sink to wash your hands. In the sink, the water usually goes around in a circle before leaving through the drain. Depending how strong and how much water comes out of the tap, that circle changes its shape and size. Something similar happens with the aurora oval. Depending on the amount and speed of particles, the oval changes shape and strength.
NOAA Space Weather Prediction Center has developed a model for the short-term forecast (30 minutes). Colors in the model show the probabilities to see auroras. Of course, it is not a viewing guarantee. Bright green is for about 30-50% and orange-red for over 80% probability. Here is the direct link for both, the Northern and Southern hemisphere.
A sudden burst of gas of an unstable magnetic field on the suns surface. Often a large amount of charged sun particles will be hurled into space at high velocity. This usually happens at sunspot regions. Usually it last for minutes but it can stretch for hours as well. Imagine an air bubble under water rising to the surface. When the bubble is breaking through the surface the bubble will burst.
A hole in the outer magnetic field (called corona) around the sun. Through it streams solar wind steadily out until the hole closes again. This can last for days or even weeks. Instead of a bursting air bubble, imagine a windy day and someone opens a window. Through it comes a strong, steady breeze until the window is closed.
Occurs when Earth’s magnetic field is hit by a strong CME or a high-speed solar wind. A strong storm usually triggers bright aurora displays which can last multiple nights. There are five classes of geomagnetic storms from G1 (weakest) to G5.
indicates the strength of geomagnetic activity. It is numbered from one to nine, with nine being the strongest. A G1 geomagnetic storm has a Kp of 5, a G5 storm a Kp of 9. This number tells us also where auroras can possibly be seen.
NOAA Space Weather Prediction Center has created maps with colored lines for Kp=3, 5, 7 and 9 in it. In that way you can check your location and Kp-value is needed for auroras possibly to appear there. Here are the links for the Kp-index map for Europe and Asia and the Kp-index map for North America.
A graph showing the real-time situation of Earth’s magnetic field. This can be compared to a seismometer for earthquakes. Horizontal flat lines indicate the field is intact while vertical outbreaks are signs for interruptions. Strong vertical outbreaks often tell us that solar wind has arrived and auroras could be seen. As an example, here the link to the magnetogram from Sodankylä, Finland.
Our sun’s activity is on a maximum once every 11 years or so, often called the Solar Max. During that time the number of sunspots and CME’s are usually high, creating a lot of auroras. Halfway through that cycle there will be solar min, when most aurora action results from coronal holes. During that time the kp-values are commonly low.
Imagine your own energy level during 24 hours. You may get up in the morning and at some point in the day you are most active. Later, while sleeping, your activity level will tend to be at a minimum.
a stream of charged particles leaving the sun. If Earth-directed it might trigger aurorae.
an area on the sun’s surface with a strong magnetic field. That field can stretch into space without being broken. The gas then has more space and therefore heat on the surface is reduced. Because of the lower temperature that area is observed as a dark spot.
To imagine the stretching magnetic field let’s think of children blowing soap bubbles. If blown carefully, the bubble can be held at the ring for a while before releasing it.
For the dark sun spots imagine a metal bar being formed into a sword. It is done when the metal is hot, having an orange glow. Once put into cold water it cools down and is darker.