Fox ­fires – an Aurora Borealis guide II: Expectations

Part I: Introduction and Terms

To have a great aurora experience, it is good to have realistic expectations. Not living in a place where auroras are visible may lead to wrong assumptions. To give you a better picture of what to expect, I will go through some common questions and answer them. As you read through, you will understand that there are many uncertainties in predicting auroras.

Are the colors as strong as in the pictures I’ve seen?
Not often, the colors of auroras are usually much weaker to the human eye. There is one big difference between a camera and our eyes. If we look at the sky for five seconds, the human eye sees every moment once. We may remember them in our brain, but our eye can see only one moment a time and erases the one before. If the camera ‘looks’ for five seconds at the sky, it adds all moments together and creates one image from all those single moments. Therefore the colors are mostly stronger in the image opposed to how we see them.
Trying to photograph auroras in its natural, pale colors and strength would most of the time result in a black landscape because there just isn’t enough light.

Copyright: Thomas Kast

How the camera sees things (developed RAW)

Copyright: Thomas Kast

Here I tried to reconstruct how it really looked like

Are there always multiple colors of auroras in the sky?
No, every night is different. Green is the most common, followed by purple, red and blue. Strong green aurora arcs have often a bit of white/purple at the lower end.

Copyright: Thomas Kast

Nothing but green

Copyright: Thomas Kast

Very colorful aurora during geomagnetical storm

Why are there different colors?
Colors appear when gas in our atmosphere is excited by incoming solar wind. Oxygen then can produce the common green color and also the red in high altitudes. The color depends how excited the gas is. Nitrogen is responsible for blue. At times these colors mix and we can see purple, white, etc.

Copyright: Thomas Kast

Common green with red high above

Copyright: Thomas Kast

Green with white and purple at the lower edge

In what shapes do auroras appear?
Shapes are determined by the strength and speed of the solar wind. Depending where you are to view auroras, some shapes may be more common than others.
Let’s go through some of the common shapes and start with the relatively calm ones, arcs, needles and curtains:
Slow, weak wind might create ‘only’ a very pale, green arc on the horizon which barely moves at all, just like a rainbow. With speed and strength picking up, an arc may be higher up and even travel all the way over the sky. There are also times when you can see multiple arcs, one almost above you and others towards the horizons).
The arc can turn into a curtain with needles rising high up in the sky and travel fast through the arc. I like to call this a curtain because it reminds me of a stage curtain in a theater. Usually I imagine someone is at one end of that curtain making waves.

Copyright: Thomas Kast

An arc stretching over the horizon with some needles.

Copyright: Thomas Kast

A curtain made of countless needles

Copyright: Thomas Kast

A green curtain over the frozen Baltic Sea

Sometimes there is no curtain, arc or needles but a fog-like glow filling half the sky.
Let’s go to the crazy stuff now, spirals, coronas and flickering
Spirals travel from the low horizon upwards and dance in curves. This is often happening with strong solar wind and over in just a few minutes. If the auroras are very strong and you are lucky, you can see a corona opening up right above in the sky. Countless rays spread out in multiple colors. This usually lasts less than a minute. After a corona there is often a kind of flickering, where parts of the sky above are randomly lit up and switched off within split-seconds.

Copyright: Thomas Kast

Spiral shaped aurora with twilight

Copyright: Thomas Kast

Corona explosion in green and purple

Can I see auroras right after sunset?
No, auroras will be visible only once the sun is about 10 degrees below the horizon. Before that, the daylight is still too strong. In autumn there can be twilight at the horizon and auroras in the sky.

Copyright: Thomas Kast

Auroras with twilight on the horizon

Are the lights dancing in the sky all night long?
Not usually, this depends on the strength and density of the particles flowing into our atmosphere. However, a long-lasting strong CME or big coronal hole can produce a show that lasts throughout the night and longer.

Can I see Northern lights every night?
No, it all depends on what is happening on the sun and solar wind leaving. If the activity on the sun is high, there can be auroras for many nights in a row. When the sun is quiet, there can be a number of nights without any auroras.

Can auroras be seen through clouds?
Yes and no, it depends on the thickness of clouds. Through a thin layer of clouds, strong auroras can be seen easily. If the sky is filled with thick clouds there is usually no chance to see any auroras.

Copyright: Thomas Kast

Auroras visible through openings in the clouds

A CME erupted, when can I expect to see auroras?
That depends on a few things. First of all, for auroras to show up, that CME must travel towards Earth or at least near it. In case it does flow towards Earth, impact is usually around 24-72 hours afterwards. However, sometimes there may be no impact recorded at all.
The estimate for time of impact not always correct, sometimes it is earlier, sometimes later. The main reason for it is speed as we can’t know for sure how much the solar wind slows down while travelling.

I read online that there should be Northern lights tonight, is that a guarantee?
By now you have probably learned that there are no guarantees. The best way to know is to go outside and look up. Of course there are tools online which can help you. These include webcams showing the night sky, magnetograms showing how the situation of Earth’s magnetic field and pages showing the expected kp-index or auroral oval. The last part of this guide consists of a list of links.

We are at the end of the second part, expectations.
Continue reading:
Part III: Preparation is everything
Part IV: Photographing auroras
Part V: Links

5 responses to “Fox ­fires – an Aurora Borealis guide II: Expectations

  1. Pingback: Fox ­fires – an Aurora Borealis guide: Introduction and Terms | 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: A Luminous Glow of the Upper Atmosphere | Atypically Epic

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