FAQ

FAQ

Most frequent questions and answers

Yes!..

As you can see on this page! Usually, the northern lights are only visible in Sweden’s northern reaches… It is possible to see the northern lights much further south than Jokkmokk, however, and during periods of particularly high solar activity, it’s not unheard of to see the aurora as far south as Stockholm and Gothenburg and even the northern parts of the United Kingdom…

Yes…
The northern lights, or aurora borealis, appear around the middle of August to around the end of March all over Sweden… But for the very best chance of seeing the northern lights you should make the trip to Torneträsk area in Abisko. If you are in the lower latitude’s near and around 60° you preferably need Solar Flares on the sun or Solar Wind.

From middle of August to May. (Depending on your location)
Anywhere from 20:00 ot Sunrise (8pm to Sunrise)
(Swedish local time)

The darkest period which is between November and February offer longer evenings for gazing at the sky, while the strongest lights normally occur during October and March between 8pm and 2am. They are also seen as early as late August and as late as mid April. This can vary dependent on your location in Sweden due to the movement of the Sun.

“Northern Lights zone” — Go above 60° latitude, to 72°. A significant portion of Sweden lies within the zone (called the ‘auroral oval’). Ideal viewing conditions are clear, and cloudless skies. But for the very best viewing conditions you should make the trip to Torneträsk (a micro climate area) in Abisko.

Solar particles collide with atmospheric gases and create colorful curtains as a result of chemistry and earths magnetic field. Bottom line: When charged particles from the sun strike atoms in Earth’s atmosphere, they cause electrons in the atoms to move to a higher-energy state (you could say they become energised). When the electrons drop back to a lower energy state, they release  photons: light. This process creates the beautiful aurora, or northern lights. [Video]

Displays can vary in intensity – from a glowing curtain of greenish yellow lights, dancing in the distance to a spectacular, multi-coloured fusion stretching across the sky. Most people lucky enough to see the aurora witness a display of neon green lights but if you are really lucky then that display might be yellow, red and purple or even multi-coloured. If the storm is intense white (light) “colours” can appear. Add the red green blue together you get white.
From experience, blue is the most rare.

The differences depend on two main factors: what type of gas is reacting with the solar particles and at what altitude this activity is taking place. Most of it occurs 100-200km above the Earth – a level where ‘excited’ nitrogen atoms glow green and blue. And above 200km, oxygen atoms glow red when reacting with charged particles from the Sun.

Anywhere from a split second to all night long. Depending on the magnitude of the incoming solar event. Coronal holes consistently produce nice auroras but big solar flares and CME’s-coronal mass ejections are responsible for global-wide aurora displays… the BIG shows!

Basically, every night, but you cannot see them when the sun. Anywhere from when the Sun sets until it rises up again. In the far north of Sweden during the season it is almost a constant Kp-index of Kp2-3, the hi latitude makes it more likely that you will see them even if they are not so strong. It is quite common that you get sightings already by 16:00 hours during storm activity.

There is always some aurora at some place on earth. When the solar wind is calm, the aurora might only be occurring at very high latitudes and might be faint, but there is still aurora. In order for us to see the aurora, however, the sky must be dark and clear. Sunlight and clouds are the biggest obstacles to auroral observations.

Sightings of the northern lights can never be guaranteed, even when the conditions seem just right. Most people appreciate that the northern lights are a natural phenomenon and we can’t turn them on for you!

But what we can do is get you to locations where sightings are generally known to be possible and better than anywhere else inside Stockholm. And what’s more, those places often offer beautiful seascapes as well as landscapes perfect for photography during the day when you are not stargazing.

Most likely, No audible sound!
There is simply not enough scientific research to prove this myth.

But Aurora is known to interfere with digital devices. So in a sense, yes, you can sometimes get static on your radio.  😉

The best answer is “Maybe.”

It is easy to say that the aurora makes no audible sound. The upper atmosphere is too thin to carry sound waves, and the aurora is so far away that it would take a sound wave five minutes to travel from an overhead aurora to the ground. But many people claim that they hear something at the same time when there is aurora in the sky. We are aware of only one case where a microphone has been able to detect audible sound associated with aurora (visit Auroral Acoustics: the web site does not have sound samples, but you’ll find a link to an in-depth paper and recent news on this topic.). The sound is often described as whistling, hissing, bristling or swooshing. What it is that gives people the sensation of hearing sound during auroral displays is an unanswered question. By searching for an answer to that question, we will probably learn more about the brain and how sensory perception works than about the aurora.

Without any doubt, Abisko in northern Sweden.

The number of sunspots on the Sun’s surface changes on a fairly regular cycle, which scientists refer to as the sun’s 11-year cycle variation. Sunspot activity, and hence auroral activity, tends to peak every 11 years. This peak is called the solar maximum. The last solar maximum was in 2014; the next is expected around 2025. The chances of seeing the aurora at lower latitudes increase when the sunspot cycle is at a maximum, but chances at higher latitudes are not as dependent on the solar maximum because the auroral oval is normally present.

FAQ - Science of the Aurora

The name ‘Aurora Borealis’ (latin) is credited to Galileo and means ‘Northern Dawn’.

Aurora Australis, South Dawn.

The aurora is a luminous glow seen around the magnetic poles of the northern and southern hemispheres. The light is caused by collisions between electrically charged particles streaming out from the sun in the solar wind that enter Earth’s atmosphere and collide with molecules and atoms of gas, primarily oxygen and nitrogen.

When the electrons and protons from the sun collide with oxygen and nitrogen in the Earth’s atmosphere, they gain energy. To get back to their normal state, they release that energy in the form of light. The principle is similar to what happens in a neon light. Electricity runs through the light fixture to excite the neon gas inside, and when the neon is excited, it gives off a brilliant light.

The dancing lights of the aurora are seen around the magnetic poles of the northern and southern hemispheres because the electrons from the sun travel along magnetic field lines in the Earth’s magnetosphere. The magnetosphere is a vast, comet-shaped bubble around our planet. As the electrons from the solar wind penetrate into the upper atmosphere, the chance of colliding with an atom or molecule increases the deeper into the atmosphere they go.

The two figures below show the locations with the most frequent occurrences of aurora borealis (left) and aurora australis (right) during the period of best viewing around the middle of the night.

This level of auroral activity, index Kp=2, will occur often enough that you will probably see the aurora if you travel to these regions when the nights are dark and stay for three days to a week, assuming that the skies are clear. If the auroral activity level is higher than 2, you will still observe the stronger motions and color changes, etc., that are seen farther equatorward.

aurora oval

 

The composition and density of the atmosphere and the altitude of the collisions determine the colors. The aurora is most often seen as a striking green, but it also occasionally shows off other colors, ranging from red to pink or blue to purple. Oxygen at about 60 miles up gives off the familiar green-yellow color, oxygen at higher altitudes (about 200 miles above Earth’s surface) gives all-red auroras. Nitrogen in different forms produces the blue and red-purple light.

The composition and density of the atmosphere and the altitude of the collisions determine the colors. The aurora is most often seen as a striking green, but it also occasionally shows off other colors, ranging from red to pink or blue to purple. Oxygen at about 60 miles up gives off the familiar green-yellow color, oxygen at higher altitudes (about 200 miles above Earth’s surface) gives all-red auroras. Nitrogen in different forms produces the blue and red-purple light.

Cameras have different sensitivities to colors than the human eye, therefore there is often more red aurora in photos than you can see with the unaided eye. Just like sunlight, which appears to be white, is a blend of the colors of the rainbow, the aurora is also a mixture of colors. The overall impression is a greenish-whitish glow. Since there is more oxygen at high altitudes, the red aurora tends to be on top of the regular green aurora. Very intense aurora often has a purple rim at the bottom. The purple results from a mixture of blue and red emissions from nitrogen molecules.

figure explaining how aurora gets its color

 

The bottom edge of the aurora is typically about 60 miles (100 kilometers) above the surface of the Earth. The top of the visible aurora peters out at about 120 to 200 miles (200 to 300 kilometers), but sometimes aurora can be seen as high as 350 miles (600 kilometers). This is about the altitude at which the International Space Station flies.

altitude of aurora

Auroral forms can be divided into broad categories based on activity level and the viewer’s perspective.  

Homogeneous arc
At its least active, the auroral curtain forms diffuse, glowing streaks hanging quietly in the sky. This form has no distinct structure.At its least active, the auroral curtain forms diffuse, glowing streaks hanging quietly in the sky. This form has no distinct structure. photo by Jan Curtis

Rayed arc
When the aurora becomes slightly more active, vertical stripes or striations, called rays, form. These are actually fine pleats in the auroral curtain.When the aurora becomes slightly more active, vertical stripes or straitions form. These are actually fine pleats in the auroral curtain.  photo by Jan Curtis

Rising vapor column
The auroral curtain sometimes appears to touch a distant mountain top or even rise like smoke. This illusion occurs because you are seeing a several-hundred mile long aurora near the horizon where perspective gives the illusion that it is touching the ground.photo courtesy of the Geophysical Institute - UAF

Corona
The aurora may appear as rays shooting out in all directions from a single point in the sky. This dramatic form occurs when you are directly beneath the swirls and folds of an active curtain. The rays are actually hundreds of miles long and perspective makes them appear to converge.photo by Jan Curtis

Scientists can predict when and where there will be aurora, but with less confidence than they can predict the regular weather. (personally I would argue it’s the other way around)

The ultimate energy source for the aurora is the solar wind. When the solar wind is calm, there tends to be minimal aurora; when the solar wind is strong and perturbed, there is a chance of intense aurora. The sun turns on its own axis once every 27 days, so an active region that produced perturbations which resulted in aurora might again cause aurora 27 days later. The solar wind takes approximately three days to get to the earth on its way from the sun. Observing the sun and predicting perturbations in the solar wind resulting from events taking place on the sun (such as flares or coronal mass ejections) provides information in a few days in advance of possible auroral displays. Spacecraft such as the Solar and Heliospheric Observatory (SOHO), Solar Terrestrial Relations Observatory (STEREO), and Solar Dynamics Observatory (SDO), provide researchers with data on activity occurring on the surface of the sun as well as in the solar magnetic field.

Another source of data used to predict the aurora comes from satellites located approximately 90 minutes or 1,500,000 km away from earth. The Deep Space Climate Observatory (DSCOVR) and Advanced Composition Explorer (ACE) Real-Time Solar Wind satellites provide real-time data to researchers about geomagnetic storms. Data from these satellites provide about one to two hours warning of an upcoming aurora.

 

 

Streams of charged particles that produce the aurora come from the corona, the outermost layer of the sun’s atmosphere. The corona is exceedingly hot, measuring more than one million degrees. The high temperature causes hydrogen atoms to split into protons and electrons. The resulting gas of charged particles is called plasma, which is electrically conductive. The solar plasma is so hot that it breaks free of the sun’s gravitational force and blows away from the surface in all directions. The movement of this plasma is called solar wind. The intensity of the solar wind and the magnetic field carried by it change constantly. When the solar wind blows stronger, we see more active and brighter aurora on Earth

The number of sunspots on the Sun’s surface changes on a fairly regular cycle, which scientists refer to as the sun’s 11-year cycle variation. Sunspot activity, and hence auroral activity, tends to peak every 11 years. This peak is called the solar maximum. The last solar maximum was in 2014; the next is expected around 2025. The chances of seeing the aurora at lower latitudes increase when the sunspot cycle is at a maximum, but chances at higher latitudes are not as dependent on the solar maximum because the auroral oval is normally present.

View solar cycle progression

The Kp number is a system of measuring aurora strength. The range goes from 0 to 9 (0 being calm, 1 very weak, all the way up to 9, which would represent a major geomagnetic storm with strong auroras visible). Anything Kp 5 and above is classified as a geomagnetic storm.

The Kp-index was introduced by a German scientist named Julius Bartels in 1939. The abbreviation Kp comes from the German “Kennziffer Planetarische,” which translates loosely as “planetary index number,” although it is better known in English as simply the planetary index, and is usually designated as Kp (number from 0 – 9).

The Kp-index is a scale used to characterize the magnitude of geomagnetic disturbances. A geomagnetic storm starts at Kp5 after which the G-scale is also used.

Example chart from NOAA showing a Kp8 storm

  • Kp0 = Quiet
  • Kp1 = Quiet
  • Kp2 = Quiet
  • Kp3 = Unsettled
  • Kp4 = Active
  • Kp5 = Minor storm (G1)
  • Kp6 = Moderate storm (G2)
  • Kp7 = Strong storm (G3)
  • Kp8 = Severe storm (G4)
  • Kp9 = Extreme storm (G5)

The K-index quantifies disturbances in the horizontal component of earth’s magnetic field with an integer in the range 0–9 with 1 being calm and 5 or more indicating a geomagnetic storm. It is derived from the maximum fluctuations of horizontal components observed on a magnetometer during a three-hour interval.

K is a measure of how much geomagnetic disturbance there is at a particular location on the globe. The higher the K number, the better the aurora. Putting it another way, the higher the K number of the aurora was, the more gutted you will be that you missed it.

Kp is a 3-hour average of K readings from across the planet.
Kp values are used for global scientific studies and have no practical use for aurora-hunters wishing to see the lights in Stockholm. We could have a major substorm in progress in the Sweden but other parts of the world are calm, so when averaged out the Kp becomes very low. What is important for aurora-hunters is the K (not Kp) value at magnetometers around 10 degrees North of their own location. To use an analogy, say the Kp was the average temperature in every capital city in the world in a three hour period, then what use would it be in finding out whether it is frosty in Stockholm at the moment?

For this reason any aurora apps, web-sites and FB groups that use Kp values are totally unreliable and should be avoided. The best solution or practice is to monitor Magnetometers. They provide the closest approximation to visible auroras in sweden.

Or you can just use our favorite app.

The National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center (SWPC) OVATION Aurora Forecast Model is updated every 30 minutes. The animation shows auroral activity that occurred over the Northern Hemisphere in the last 24 hours. Fast forward to the last few seconds of the animation to see what is predicted for the next 30 minutes.

The aurora is not visible during daylight hours.  Therefore, the model indicates the sunlit side of Earth in blue and the nightside hours in grayscale.

Remote sensing spacecraft also monitor the sun for indications of impulsive eruptions that eject material toward Earth, or regions where continuous high-speed streams of material are escaping and heading Earthward. In either case, the travel time to Earth for such material leaving the sun is 1 to 3 days. This allows good forecasts to be made on these look-ahead time scales, based on events and conditions observed on the sun.

Just as Earth rotates on its axis making a complete rotation every 24 hours, the sun spins on an axis making a complete rotation in 27 days. Solar phenomena on the surface of the sun distribute high speed plasmas that often result in increased auroral activity on earth. These phenomena may be sunspots, coronal mass ejection, filaments, or a prominence. As the sun rotates, the solar phenomena and resulting areas of high-speed plasma are likely to reoccur every 27 days until the phenomena dissipate. Therefore, if there is high auroral activity today it’s possible that there will be high auroral activity again in 27 days. This 27 day rotation is called a Carrington Rotation.

 

Magnetometers provide an alternative view of the level of geomagnetic disturbance occurring. A sudden steep change in the magnetometer is usually an indicator that an extended period (0.5 hours or more) of active aurora is beginning. This is especially true before 2 or 3 a.m. Scientists also find it helpful to see the time history of the magnetometer trace, since other indicators, like the all-sky camera, only show current conditions.

When the Earth is passing through a plasma cloud, the collisions of charged particles in the upper atmosphere cause disturbance to the Earth’s geomagnetic field. A magnetometer is a device that measures deviations in the Earth’s magnetic field, which might indicate that there is an aurora in progress. The greater the disturbance, the better the aurora is likely to be. The relationship between magnetometer readings and actual auroras in the sky is quite complex. It is possible to have strong auroras in the sky when the magnetometers are at seemingly background levels. Norwegian magnetometers provide the best correlation to visible auroras than UK-based ones. In many cases, UK magnetometers fail to detect activity or react a couple of hours after the light show started.

Visit the magnetometer monitor for a chart of the current conditions.

The term “cosmic weather” is usually understood as a set of phenomena on the Sun, in the upper atmosphere, near-Earth space and interplanetary medium, affecting the processes in near-Earth space.

Observations of space weather are associated with the monitoring of processes occurring in outer space and the initiator of which, in one way or another, is the sun. These processes can affect public infrastructure systems, including telecommunications systems and avionics, biological objects (i.e., they can affect people’s health).

The primary source of disturbances are variations of solar radiation, and the transfer of disturbances is carried out by waves and particles in the interplanetary medium, the magnetosphere, and the Earth’s ionosphere. First of all, these disturbances affect those processes in which the steady balance of electric currents and magnetic fields plays a significant role. Disturbances that disturb this equilibrium can lead to various emergency situations not only in navigation, communications, electric power, but also in seemingly weakly related industries, such as extinguishing forest fires, pumping oil through pipelines or healthcare.

Auroral currents can cause damage to power lines and corrosion in oil and gas pipelines. Magnetic storms, accompanied by the emergence of ionospheric irregularities, prevent the propagation of RF radio and navigation signals from GPS satellites, and the polar cap absorption (PCA) can severely hinder or completely terminate RF communications on transpolar flight lines, requiring changes in flight routes to lower latitudes. Irradiation of spacecraft with energetic particles of solar flares and the radiation belts of the Earth can cause equipment failures, damage to solar batteries and sensors.

An aurora, or what scientists call a ‘Geomagnetic Substorm’ or ‘Polar Magnetic Substorm’, goes through three distinct phases:

  1. Growth
  2. Expansion
  3. Recovery

Acknowledgement Glendale App

The Growth Phase usually starts around 1-2 hours before the expansion phase, although it can start several hours before. It is where we see a very slow fading-in of the aurora as a pink/red band that is approximately 10 degrees high on the Isle of Skye and sits above the horizon. It typically coincides with a climb in the magnetometer plots. This type of aurora is called a ‘diffuse aurora’. During the growth phase, the diffuse aurora gets brighter and the discrete green arc begins to rise up over the horizon inside it. We can use this to get advance warning of the expansion phase and approximate when it might start.

Acknowledgement Glendale App

The Expansion Phase is the one that aurora-hunters seek, as this is when the aurora explodes into the brightest colours and biggest rays. It is when the magnetometers dip sharply downwards.

Acknowledgement Glendale App

In the Recovery Phase, the intense burst of activity during the expansion phase is waning and the magnetometers are returning to background levels. The aurora can remain for many hours after the magnetometers have normalised.

Acknowledgement Glendale App

A phenomenon, in a scientific context, is something that is observed to occur or to exist. This meaning contrasts with the understanding of the word in general usage, as something extraordinary or outstanding.

Phenomena are categorized in a number of ways. Natural phenomena are those that occur or manifest without human input. Examples of natural phenomena include gravity, tides, biological processes and oscillation.

Here are a few of the many possibilities, types of natural phenomena include: Weather, fog, thunder, tornadoes; biological processes, decomposition, germination; physical processes, wave propagation, erosion; tidal flow, and natural disasters such as electromagnetic pulses, volcanic eruptions, and earthquakes.

  • Social phenomena are those that occur or exist through the actions of groups of humans. Six degrees of separation, for example, is a phenomenon that is demonstrated in social networking.
  • Psychological phenomena are those manifested in human behaviors and responses. The sunk cost effect, for example, is the tendency for humans to continue investing in something that clearly isn’t working. Another psychological phenomenon, the Hawthorne effect is demonstrated by an improvement in human behavior or performance as a result of increased attention from superiors, clients or colleagues.
  • Visual phenomena include optical illusions, such as the peripheral drift illusion in which people perceive movement in static images like Kitaoka Akiyoshi’s rotating snakes.

The word phenomenon is derived from the Greek verb phainein, which means to show, shine, appear, to manifest or to be manifest.

Space Weather Prediction Center https:www.swpc.noaa.gov

The Ap index quantifies the global daily average activity level of the geomagnetic field. The 27-day forecast of the Ap index is performed using the Auto-regressive Integrated Moving Average (ARIMA) method and it is based on the work of McPherron (1999) in their paper “Predicting the Ap index from past behavior and solar wind velocity” [doi:10.1016/S1464-1917(98)00006-3]. The Ap forecast is based on identifying recurring geomagnetic activity. Thus, it will not forecast transient activity. This will also affect the quality depending on the solar cycle, with best results in the declining phase, while almost random results otherwise.

The Ap-index provides a daily average level for geomagnetic activity. Because of the non-linear relationship of the K-scale to magnetometer fluctuations, it is not meaningful to take the average of a set of K-indices. Instead, every 3-hour K-value will be converted back into a linear scale called the a-index. The average from 8 daily a-values gives us the Ap-index of a certain day. The Ap-index is thus a geomagnetic activity index where days with high levels of geomagnetic activity have a higher daily Ap-value.

How do you determine the Ap-index?
The daily Ap-value is obtained by averaging the eight 3-hour values of ap for each day. To get the these ap-values you first need to convert the 3-hour Kp-values to ap-values. Be aware that we use the official, finalized Kp which comes from the GFZ in Potsdam, Germany. This Kp-index works slightly different then the preliminary Kp-index. Read about this in our Kp-index help article. To make it a bit more clear on how you can determine the Ap for a certain day, we will work with an example: we take one day with the following measured Kp-values: 0+, 2-, 2o, 3o, 7-, 8o, 9- and 9o. The next step would be to convert these Kp-values to ap-values. The table at the bottom of this article will help you with this. When we are done converting we get these eight ap-values: 2, 6, 7, 15, 111, 207, 300 and 400. The average of these eight values will give you the Ap for that day. The day that we used in this example day would have an Ap-value of 131. The table below will let you convert the Kp-values to ap-values.

Bz and Bt are measures of the strength and direction of the interplanetary magnetic field between Earth and Sun. Using a simple analogy, think of the aurora as being like the light from a rechargeable torch. When the Bz is south (negative), the torch is charging. How long the light lasts, and how bright the display, depends on how long it was on charge and how strong the charge was.

German Research Centre for Geosciences.

G1, G2 and G3 are alternative names for Kp 5, Kp 6 and Kp 7 respectively.

A Coronal Mass Ejection is a plasma blob that the sun periodically emits from active sun-spots. If the blob hits the earth’s atmosphere it can cause some of the best auroras. It is rare to get a direct hit. Think of it like the sun sneezing and the chance of some of the snot hitting an 8000 mile wide rock that is 93 million miles away.

CME’s are often described as ‘full halo’ or ‘partial halo’, and ‘symmetric’ or ‘asymmetric’. ‘Full halo’ means a nice even spray of plasma. ‘Partial halo’ means a lumpy, uneven spray of plasma. ‘Symmetric’ means directly aimed at Earth. ‘Asymmetric’ means slightly skewed to one side, so not a direct hit. The ideal is a full halo, symmetric CME which will give a nice even spray of plasma aimed directly at us.

When the sun launches an earth-directed CME, it takes 2 to 3 days to reach the Earth.

Using the above analogy, if a CME is a sneeze then a Coronal Hole High Speed Stream is runny nose. It is a constant leak of plasma from a hole in the sun’s magnetic field that sprays out into space. When one of the coronal holes is facing towards the earth, we can have a gentle dribble of snot hitting our atmosphere and causing auroras that are less intense than those caused by CMEs but continue for days rather than hours.

Between nautical and astronomical twilight end times, it is not unusual for your test photo to capture a sky that is largely purple or navy blue. This is not an aurora, it is the refraction of the sunlight causing blues, indigos and violets of the colour spectrum to become visible.

In the 99% of cases this is light pollution. But otherwise orange aurora is possible, very rare, usually not seen by naked eye.

Does not physically affect aurora. But it does affect the visibility of it, due to extra light in the sky.

On a clear night, the moon can actually improve the quality of your aurora photos by illuminating the landscape and, thereby, significantly reducing camera noise. The colours of the aurora take on lovely pastel shades and the images are quite stunning. However, when there is a big moon and very fine misty cloud, the clouds will be lit by the moon and make it difficult to photograph the aurora. This is because increasing the exposure to bring out the aurora colours will also amplify the moonlight on the clouds. When the moon is at 25-50% it gives the optimal illumination to the landscape without washing out the more subtle details and colours of the aurora.

 

The European Centre for Medium-Range Weather Forecasts https://www.ecmwf.int/