Fox ­fires – an Aurora Borealis guide: Introduction and Terms

Aurora borealis – just hearing those words make me look outside and check for clear skies. The mystic dancing lights are a big part of my life and with many people asking me questions about them, I decided to write this guide.

Many different 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’s 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’ll ever be lucky enough to see that fox..

Copyright: Thomas Kast

Just missed the fox..

This guide consists of five parts and my goal is to help you
– 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 proove to have higher viewing probabilities, but there is no guarantee to see auroras in certain colors at a certain time in a 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.

Copyright: Thomas Kast

Auroras are reflected in this calm lake with a satellite flare.

 

Terms

In this section I will go through 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.

Aurora borealis
A display of light in the night sky of the Northern hemisphere. It is caused by charged particles from the sun. When these particles reach Earth, they collide with atoms in our atmosphere and create light in certain colors. Think of it like raindrops colliding with sun light producing a colorful rainbow.
The name comes from the words Aurora (the Roman goddess of dawn) and boreal (the Greek name for north wind). Northern lights is another name for aurora borealis. Auroras (or more correctly aurorae) in the Southern hemisphere are called Aurora australis.

Auroral oval
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 (20 minutes). Colored areas show where are possibilities to see auroras, it is however not a viewing guarantee. Here are the links for the Northern hemisphere and for the Southern hemisphere.

CME
short for Coronal Mass Ejection. It stands for a sudden burst of gas (solar wind) leaving the sun’s surface. This mainly happens at sunspots. Imagine an air bubble under water rising to the surface. When the bubble is breaking through the surface the bubble will burst.

Coronal hole
a certain magnetic field in the sun’s atmosphere allows solar wind to stream into space. 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.

Geomagnetic storm
Occurs when Earth’s magnetic field is hit by a strong CME or a high-speed solar wind. A storm usually triggers bright aurora displays. There are five classes of geomagnetic storms from G1 (weakest) to G5.

Kp-index
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.

Magnetogram
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.

Solar cycle
Our sun’s activity is on a maximum once every 11 years or so, often called 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 not much is happening on the sun’s surface apart from coronal holes.
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.

Solar wind
a stream of charged particles leaving the sun. If Earth-directed it might trigger aurorae

Sunspot
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.

This concludes the first part; getting started and explaining some common terms.
Continue reading
Part II: Expectations
Part III: Preparation is everything
Part IV: Photographing auroras
Part V: Links

If you have questions, comments or any other feedback, feel free to write!

6 responses to “Fox ­fires – an Aurora Borealis guide: Introduction and Terms

  1. Pingback: Fox ­fires – an Aurora Borealis guide II: Expectations | Salamapaja

  2. Pingback: Fox ­fires – an Aurora Borealis guide III: Preparation is everything | Salamapaja

  3. Pingback: Fox ­fires – an Aurora Borealis guide IV: Photographing auroras | Salamapaja

  4. Pingback: Fox ­fires – an Aurora Borealis guide V: Links | Salamapaja

  5. Pingback: NASA’s Solar Dynamics Observatory is monitoring a large coronal hole in the sun’s northern hemisphere | boldcorsicanflame's Blog

  6. Pingback: Best Place to See Northern Lights | Bangari Content Gallery

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