Seeing Auroras

What do auroras look like?

Auroras appear to the naked eye as a very faint, white glow in the night sky to the magnetic northsouth. Many auroras are totally invisible to the naked eye or can only be seen by looking at them indirectly, i.e. out of the corner of your eye. It is extremely rare to see them in colour with the naked eye.

How do I see the aurora?

To 'see' the colours of an aurora, you need a digital camera or a modern smartphone. Take a test photograph of the sky to the northsouth, using the settings I suggest below. Then view the image on the telly on the back of the camera and look for green. If you see a strong green arc then there is an aurora present.

Wait until it is dark. Generally the earliest time you can capture the aurora is mid-way between the end of nautical twilight and astronomical twilight at your location.

Will I see it with my naked eyes?

You will never see an aurora with the naked eye that looks like the photographs taken on the same night. Cameras, using long exposures, are much more sensitive than the human eye. They capture colours and details that are impossible for the human eye to detect.

There are also major differences in ability to see in the dark from person to person. I have stood side-by-side watching an aurora with someone who could see red & green colours with their eyes, when all I was seeing were shades of white (monochrome). Conversely, I can see extreme sub-visual auroras with my naked eye that are invisible to those with keener night-time, colour vision.

These two photos illustrate how a strong aurora appears to the naked eye compared to what the camera captures.

Aurora to the naked eye

Same aurora on camera

Those tall, vertical rays are irregular during an aurora, so imagine the top photo without the columns to get an idea how the aurora typically appears to the naked eye. Yes, many people are underwhelmed and disappointed when they first see an aurora using their naked eyes but photograph one and you will be addicted forever.

Low cloud, mist, light pollution, airglow, moonlight, etc. can easily be mistaken for auroras when using the naked eye, which is why you must always use a camera to be 100% certain.

Cameras are to aurora-watchers what binoculars are to bird-watchers.

Best Place & Time

Where is the best place to see the aurora?

The closest place to where you are staying that has a clear view of the horizon to the northsouth and is without light pollution. Ideally, a view to the northsouth over the sea or a loch is best.

When is the best time of day?

Most auroral substorms peak between 19:00 and 23:00 UTC, with a bias towards 22:00 UTC. The activity can be very short-lived, so it is important to use my app to alert you when the aurora is starting otherwise you could easily miss the active period.

If the aurora is fairly static, it will appear to get stronger towards the local midnight (around 00:30 GMT in winter or 01:30 BST in summer on Skye) simply because the background sky is at its darkest then and because your latitude will be closer to the point where the auroral oval extends furthest southnorth.

When there is a moon, the best time is before the moon rises or after it has set.

When is the best time of year?

You cannot see auroras on Skye in June and July because it is too light at night.You can see auroras all year round in Australia and New Zealand. The best times of year are October through to MarchMarch through to October. The best months for aurora are around the equinoxes: March, September and October.

How often do auroras occur?

In a typical year, I usually capture discrete auroras on camera on at least 60 nights, rising to almost 120 nights in a good year, so on average around twice a week here on the Isle of Skye. There are also many more nights when I get the weaker diffuse auroras on camera.

I'm visiting Skye in xxx week's/month's time, will I see it?

There are three factors that are essential to getting an aurora: geomagnetic activity, clear sky and darkness. It is very difficult to achieve all three of these things at the same time, particularly at certain times of year, e.g. in June/July it never gets dark at night.

In the summer months, the window of darkness is very short, so the chances of meeting all three criteria is much lower. In winter, the period of darkness is much longer, so the chance of getting auroras is much higher.

At all times of year, cloud is the main limiting factor that prevents us from seeing the aurora. There would be a photographable aurora in northern Scotland almost every night if not for the cloud.

I'm on Skye tonight/tomorrow/at the weekend, will I see it?

The answer is always "maybe". It depends on clear sky, darkness and geomagnetic activity. We can be expecting major activity but see nothing because it arrives during daylight or when we have 100% cloud cover. Alternatively, we can be expecting nothing and still get auroras showing spontaneously. There is no way of knowing for certain until darkness falls on the night in question.

There is always a chance of an aurora if it is a clear night. There are more auroras than clear skies.

I've got clear sky tonight. Will I see anything?

There is no point asking anybody else. Go outside and take a test photo, then you will have your answer.

I'm on Skye, so I drive to Glendale to catch the aurora, right?

Wrong!!!! Absolutely not! The aurora is in the sky somewhere near IcelandAntarctica. Driving to Glendale will only increase your chances of missing the show and increase your chances of having an accident driving on unfamiliar, single-track roads in the dark. Go to the closest place to where you are staying that has a clear view of the horizon to the northsouth. This might even be your own garden.

You do NOT drive to find the aurora, you drive to find clear sky. If there is clear sky where you are and no aurora, you won't find it in the car.

Why do you get so many auroras in Glendale?

I take regular test photos of the night sky, 365 days of the year, to check the state of the aurora. By doing this I can tell in advance when an aurora is emerging. This gives me advance warning of if or when a show is likely to occur. I also developed an app that alerts me with 100% accuracy when the aurora is about to start.

Can I see the aurora in other parts of the UK?

If I am posting photographs of the aurora in Glendale then it can be photographed anywhere in the UK but with a caveat that for every two degrees of latitude further southnorth you will need to increase the exposure on your camera by 1 stop relative to what I am using. My latitude is 57.5°N. If I am photographing the aurora at F4 ISO800 30s then at Bamburgh in NE England (55.6°N) you would need to use exposures of F2.8 ISO800 30s or F4 ISO1600 30s or F4 ISO800 60s. The aurora will also subtend a lower angle in the sky relative to what you see in my photos by 2 degrees for every 1 degrees of latitude further southnorth that you are.

Anything Tonight? Forecast?

Are you getting anything tonight?

The first place to look for information is my Aurora Alert App which automatically updates every minute with information on the current aurora situation.

I always post photos on the Glendale Skye Auroras Facebook Page if I am getting the aurora on camera or by eye. You should make sure that you follow the page and have switched on 'notifications' and 'show first', if you want to be sure of seeing the latest updates. If you have clear sky it is always worth taking test photos at regular intervals to see whether you get any green.

Are Auroras Predictable?

Contrary to popular belief, auroras are highly predictable. Most auroras are caused by coronal holes, which can be reliably predicted 27 days in advance. Auroral substorms can be seen developing up to several hours in advance. Optimal IMF conditions can be seen arriving over an hour ahead.

The closer we get to an aurora starting, the easier it becomes to predict that it is imminent. The Glendale App is continually monitoring every condition needed for an auroral substorm to occur and advising / alerting when you need to head out.

Glendale App can accurately predict the time that activity will start 1 to 2 hours in advance.

Getting Alerts

Can I Get Your Aurora Alerts on my Mobile Phone?

I currently have an instant messaging system operating for Android phones that use the Chrome browser. This essentially works on any smartphone except iPhones provided that you have Google Chrome as the default browser. It only takes a few clicks to enable my alerts, as follows:

1. Click Aurora Alerts
2. Click 'Enable Aurora Alerts'.
3. Click 'Allow Updates'.

If you aren't sure whether your phone is compatible, just try the above steps and it will tell you if it is not supported. If your phone is Android and this does not work, download the Chrome browser from the app store and then try again using Chrome when you are prompted which browser to use at step 1.

Can I Get Your Aurora Alerts on my iPhone?

To get my alerts on iOS devices, you need to use Telegram.

Telegram

You can also get alerts on any device via the Telegram messaging app:

1. Download the Telegram App.
2. Follow Aurora Alerts UK (Glendale App).
3. Switch on notifications for the app.

What Aurora Alert Apps do you recommend?

I recommend that you use my own web app, which is designed by an experienced aurora-hunter for aurora-hunters. It provides all the essential tools that I use to predict auroras and provides instantaneous alerts. It is the only 100% accurate aurora alert app for all countries.

I would advise you to avoid all other apps! Any that are based on predicted Kp values are utterly useless. I have programmed the Glendale App to analyse all of the satellite and magnetometer data that I use and automatically issue accurate forecasts and alerts.

Photographing Auroras

What settings do you use on your camera?

These are the settings I use for my test photos, with some recommendations alongside:

• Switch the camera to 'M' or Manual.
• Switch the lens to manual (If you don't the camera will refuse to take a photo).
• Focus manually at infinity (if you don't the photos will be blurred).
• ISO 6400 to 1600 (to start with but see tips below).
• F4 (or lower, the wider the aperture the better).
• 16mm - 28mm (zooming on budget lenses will close up the aperture, so use the shorter focal length).
• 20-30s shutter speed.
• The normal settings I use on a full-frame camera are ISO 6400 F2.8 20s 28mm.
• Auto White-Balance (never use any other types, especially not 'tungsten').
• Use the 2s or 10s delay timer on the camera to open the shutter.
• Use a tripod, wall or fence post (I use the bird table).
• Never use a flash (make sure it is disabled).
• Remove all filters (they reduce light and leaving the clear UV filter on causes concentric rings of moiré on night shots).
• Shoot in RAW or RAW+JPEG.
• Turn down the LCD brightness on your camera to almost as low as it will go (No. 2 on Canon). Otherwise, you will under-expose your pics.
• Turn on the highlight blinkies on your camera so that you will know if highlights blow and can reduce the settings accordingly.

Do you have any tips for photographing auroras?

If the aurora is exceptionally bright in your test photo, always reduce the ISO in preference to the shutter speed, as this will reduce camera noise or graininess. Don't even think about reducing the shutter speed until you have reached an ISO level at which your camera produces acceptable amounts of noise. Never close up the aperture, you should always keep to the lowest F-number your lens can support.

Ordinarily on crop-sensors, if you have the settings I recommend above, the only setting you should need to adjust when you are out photographing the aurora is the ISO. All of the other settings should remain constant and you simply adjust the ISO to compensate for changes in the strength of the aurora during the show. I configure my camera to adjust ISO in steps of 1 stop, just because it makes the maths easier and takes fewer clicks to adjust it up or down.

Modern full-frame cameras are much less susceptible to noise and when using these I tend to leave the settings on ISO 6400 F2.8. I then only adjust the shutter speed when out photographing the aurora. During very bright/active shows, the shorter shutter speeds capture more detail in intricate structure of the aurora.

If your test photo is very dark, make sure that you have set the exposure to 30s, but then increase the ISO until it becomes nicely exposed.

Always make sure that there is some landscape, building or scenery in your aurora photo to give some scale or perspective. Never just shoot at the sky, unless you are lucky enough to experience a corona (overhead aurora).

Never make any adjustments in your photo-editing software that change the colours from those that your camera originally captured. This results in photos that look 'cartoonish' and totally unnatural, a.k.a. 'clown vomit'.

Practice taking night shots on clear nights when there is no aurora, so that you know what you are doing when the aurora shows. The thing most people have problems with is the focus. Until you can take a nice, sharp, night-time, landscape photo that looks like daylight but with stars, you will not be able to capture an aurora.

Think carefully about your choice of lens and focal length. Ultra-wide angle lenses are ideal for milky way and arctic auroras but not the best choice for auroras seen from lower latitudes like the UKhigher latitudes like Victoria.

A good time to practice is between the end of nautical twilight and astro twilight at your location. This is when the sky often turns purple and there is still some sunlight in the sky but stars will be showing. This allows you to simulate the kinds of exposures needed to capture auroras.

When an aurora is throwing up rays, reducing the exposure to 15s produces better clarity in the photo. However, to maintain the same brightness, this requires the ISO to be doubled. This is fine if you have a high-end, full frame camera but on normal 'crop' cameras the extra noise will be detrimental to the image quality. In my experience here on Skye, varying between 15s or 30s doesn't make enough difference to the capture of auroral rays to warrant the extra graininess. On 'crop' cameras, it is generally better to leave the exposure at 30s to get as much light into the camera as possible.

When I head out to shoot nightscapes, I take only the camera and lens, pre-fitted to the tripod, spare battery, lens cloth, a small plastic bag and a head torch. I do NOT take lens caps, camera bags, remote releases, gadgets or anything else that I might drop and lose in the dark. The plastic bag is to put over the camera if there is a rain shower.

Buy a high quality head torch, they are very light, extremely powerful and the batteries last an eternity. I recommend the Petzl Tikka Active head torches, e.g. the Tikka XP Plus, which are worth every single penny.

I used exactly the camera settings you recommended and I'm not getting anything?

Assuming you are pointing the camera northsouth, and you know from my app that an aurora was in progress at the time, the short answer is that you have made a mistake with the settings. Common errors are setting the exposure to 30 (thirtieth of a second) instead of 30" (thirty seconds) and setting the ISO to 160 or 640, instead of 1600 or 6400, respectively.

Can I video the aurora?

Not really well in the UK, Australia or New Zealand, it is not bright enough. When you have seen 'video' footage of auroras this is normally done using time-lapse photography, where many hundreds of long-exposure, still images are joined together to create a short piece of video.

There are now some modern cameras that are capable of capturing real-time video footage of auroras but they are expensive and need to operate at extremely high ISO settings. We rarely get auroras in the UK, Australia or New Zealand that are strong enough or fast-moving enough, so time-lapse is generally more appropriate for creating video in these countries.

Can I photograph the aurora on my mobile phone?

The cameras on the latest mobile phones can capture auroras, even hand-held, but you can significantly increase the image quality if you can stabilise the camera using a cradle/holder mounted on a sturdy tripod to keep the camera completely still. Make sure you:

1. Switch the camera to 'night' or 'astro' mode.
2. Set the focus to 'far'.
3. Disable the flash.
4. Enable the 2 or 10 second delay timer.

If the phone detects that it is totally still (not being held in the hand), it will run a full 30s exposure followed by a 30s noise reduction cycle, and give a pretty high quality image. The cradles for tripod-mounting only cost a few pounds on Ebay. You can also stabilise the phone by propping it up on a wall or fence post but will be difficult to get the camera angled correctly towards the aurora.

You don't need to fret about manually setting ISO, aperture and exposure length on phones. If it has a night/astro mode it will sort it all for you automatically.

Terminology Explained

What's a Substorm

Substorms are the process by which the aurora is created. Charged particles from the sun become trapped by the magnetic field on the dark side of the Earth and continue to pile up until the magnetic field snaps. This 'snap' catapults the particles into the Earth's atmosphere and triggers the aurora.

The trapping of the particles is called the 'Growth' phase. The point when the magnetic field cannot hold any more, and snaps, is called 'Onset'. The phase when the particles are catapulting into the atmosphere is called 'Expansion' and is the most important, as it is when the aurora is highly active. The 'recovery' phase is when the process starts to wind down and the magnetic field relaxes back to normal.

The Glendale App is the only app / website that tracks the substorm cycle in real-time, advising in advance when a subtorm is developing and alerting when the onset happens and the aurora builds in strength.

Substorms are like buses. If you miss one, you can just wait for the next one. They come along several times a day. The expansion phase can be very short, often less than 30 minutes, so it is vital to use Glendale App to ensure that you do not miss the best of the action.

How do I find out the Astronomical Twilight Time?

My app has all the essential times that you need for aurora-watching. It gives you the times for the coming night, rather than the current day, so it is more useful than other time and date apps. It also gives times that are precise for your specific location.

What do the angles mean, such as 'Green 10. Pink 15.'?

The height of the aurora above the horizon is a measure of how strong the display is and also how far southnorth it can be photographed.

The angles are measured by holding out your fist at arm's length in front of you, with your thumb up and the bottom of your fist lined up with the horizon. Each of your four fingers is then approximately 2.5 degrees high, so 10 degrees for the height of your fist. It is essential to keep your arm straight/stiff. Do not draw your fist towards your face.

The angles I quote in my alerts are the height to the top edge of the green and pinks arcs of the aurora above the horizon. A 'normal' aurora on Skye has green to 10 degrees. A strong aurora has green to 15 degrees. A very strong aurora has green to 20 degrees. Above 30 degrees is a major aurora.

What are 'Diffuse' and 'Discrete' Auroras?

When an aurora is just starting or ending it appears as a fuzzy red/pink band above the horizon on camera, which is known as a 'diffuse' aurora. Once the aurora forms distinct coloured bands of pink and green, shows rays and structure, or has a distinct band of clear sky between it and the horizon, it has become 'discrete'.

See my Photographic Guide to the Lifecycle of an Aurora for photographs illustrating how an aurora transitions from diffuse to discrete.

What's a Magnetometer?

When the Earth is passing through a plasma cloud, the substorm process creates electric currents that 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.

See my Photographic Guide to the Lifecycle of an Aurora for a full explanation of the relationship between Magnetometer readings and the lights in the sky.

What's a Geomagnetic Substorm and Growth/Expansion/Recovery Phases?

See my Photographic Guide to the Lifecycle of an Aurora for a full explanation the phases of a Polar Substorm and photographs of how each phase appears on camera.

What's a Kp or K Index?

K is an average measure of how much geomagnetic disturbance there is at a particular location in a 3-hour period.

Kp is an 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 anywhere in the world. There could be a major substorm in progress in your country 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 actual value at magnetometers close to 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 London at the moment?

Contrary to false information widely propagated on the internet, Kp does NOT indicate which latitudes the aurora can be seen at.

Kp is NOT an indicator that works in the northern hemisphere but does not work for the southern hemisphere. It does NOT work for ANY hemisphere.

You will very often see people posting photos of a fabulous aurora on social media and saying 'it was only Kp 1'. They might as well say 'the FTSE index of share prices was only 1000' or 'the price of oil was $100 a barrel'. Kp has equally no relevance to aurora.

For these reasons any aurora apps, websites and FB groups that use Kp or K values are totally unreliable and should be avoided. If you feel the need to monitor 'plots' then the substorm strength indicator in Glendale App provides the most accurate approximation to visible auroras anywhere in the world.

What are G1, G2 and G3?

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

What's Hemispheric Power?

HP, HPI or hemispheric power is just a simple function of solar wind speed, density and IMF. It has no practical use for aurora-hunting, as it takes no account of the substorm process. If the speed and density are high it will give a high figure even when no substorm is active and, therefore, no aurora is happening.

HP is the same value used to generate the 'ovation model' or 'aurora maps' seen on many apps and websites. These will appear to show aurora even when no aurora is happening because they are based purely on solar wind and IMF data measured a million miles from Earth.

HP does not indicate which latitudes the aurora will be visible at, as it takes no account of the strength of any substorm.

HP is not a measure of how much 'charge' is accumulating in the substorm, as it does not include a model of the magnetospheric loading and unloading cycle. HP is a purely theoretical imagining, that substorms don't exist and auroras are driven directly by the solar wind.

For this reason all apps, websites and FB groups that rely on HP or 'ovation/aurora' maps are totally unreliable and should be avoided.

What's a CME?

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.

What's a CH HSS?

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.

What are Bz and Bt?

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.

See my Photographic Guide to the Lifecycle of an Aurora for an example of how Bz, Bt and Magnetometer readings affect the lights in the sky.

Pitfalls

I saw a green arc in the sky at sunset, is that an aurora?

No. When the sun is setting, refraction splits the light into the colours of the rainbow: red, orange, yellow, green, blue, indigo, violet. Arcs of each colour appear above the horizon where the sun is going down, the typical colours of a beautiful sunset. There is often a wide, green band around the sunset. Blue, indigo and violet are not strong enough to show until the sun is well below the horizon.

If you get green or purple on camera before the astronomical twilight ends at your location, it could just be sunlight, so wait until after astronomical twilight ends and then take another photo to confirm that the colour is still there.

The sky was purple, is that an aurora?

Between nautical and astronomical twilight end times, it is not unusual for your test photo to capture a sky that is largely pink, 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.

I saw an orange glow in the sky, is that an aurora?

No. Orangey glows in the sky, particularly when reflected on clouds or visible in colour as orange by eye, are caused by light pollution from human settlements. The way to tell if a patch of colour is genuine is that you will have stars in it on your test photo.

How does the Moon affect auroras?

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.

Pitfalls of Kp

I've written a concise summary of Kp in the Terminology section above. However, I thought I should give a more in-depth explanation of why Kp is so bad for aurora-hunting and why its users live in constant confusion. It's a twisted, complicated tale. You will see some utter rubbish written on the internet, so let me try to put the record straight...

K

Let's start with 'K' without the 'p'. It's a three-hour average magnetometer deflection at a single station converted into a neat figure from 0 to 9. Zero being no activity. Nine being maximum activity.

The 3 hour periods are not rolling, they are fixed periods: midnight to 3am, 3am to 6am, 6am to 9am, and so on.

This means that if a typical one-hour substorm expansion spans the boundary between periods, say it peaks at 6am, half an hour will fall into the first slot and half an hour will fall into the second slot. Both K figures will then barely register any activity, when it could have been a nice strong aurora from the substorm.

Remember that K is just a three-hour average, at a single magnetometer, at a single place on Earth. Things get a whole lot worse...

Official Kp

Now let's think about Kp, with the 'p' for 'planetary'. Here the K values from 13 fixed locations are averaged to create a theoretical K value for the whole planet.

Take our typical one-hour substorm spanning 6am. We averaged 30 minutes of that activity into each of two K periods. Then we are now going to divide those by 13 when we average them again to make Kp. So the activity from our lovely auroral substorm at 6am has been almost totally wiped out in the Kp figures for 3am-6am and 6am-9am.

The 'official' Kp is not available in real-time. It is only available a few weeks after the event. That is because not all of the readings from the 13 stations are available online and also there is a monthly normalisation process before figures can be released.

Instead of scientists realising that Kp wasn't fit for purpose and coming up with something sensible, one bright spark came up with the idea of making a 'real-time' version of Kp. Thus was born Wing's Kp.

Wing Kp

Wing's theory was that you could guess what the Kp would be at the end of each 3-hour recording period by using a function of the real-time readings from a handful magnetometers and real-time IMF/Solar Wind data.

Unfortunately, rather than shooting this nonsense down in a shower of flames, a lot of science sites and apps ran with it.

Thus were born many of those awful sites that spew out information like the "Kp will be 4.33 in 40 minutes".

After Wing Kp, you might think things couldn't get much worse but it does...

Forecast Kp.

Twice a day the NOAA SWPC produce a forecast of what they predict the Kp to be in every 3-hour period for the next three days. It's guesswork. They factor in predicted space weather events and what happened the previous month then take a stab at what the Kp figures might be.

A lot of sites and apps just tell you the Kp that NOAA thought it would be, at the times NOAA guessed it would happen. They don't even attempt to use anything vaguely magnetometer or Wing-based.

When NOAA are predicting a Kp 7 at 6-9pm, these apps show Kp 7 when the time is 6-9pm, even when the actual activity happened hours earlier or hasn't arrived yet. That leaves users scratching their heads because they think the app is telling them what is actually happening.

Surely, that is the end of the madness? Nope...

Estimated Planetary K

This is another flavour of Kp developed by the NOAA SWPC. It is the basis of all of their Kp graphs and space weather alerts. The same being cloned by the popular aggregator sites and apps, which use it for their own graphs and Kp alerts.

Estimated Planetary K is a slightly improved version of Wing Kp, which appears to be based largely around readings at the Boulder magnetometer in the US. It's still won't help you for aurora-hunting.

Conclusion

I see a lot of confused people asking on social media what the Kp is now because one of their apps is saying Kp 7 but another is saying Kp 1. They invariably get answered with a whole new set of garbage figures. The reason is that people are comparing apps that are using totally different flavours of Kp.

The only way to have total confidence about what is happening now is to use the Glendale App. Ignore any app or site that uses Kp for aurora.

When I created Glendale App, I had no intention of making the same mistakes that the scientists had made. I came up with my own system that I called 'substorm strength'. It does everything that Kp is supposed to do, in real-time, to one minute accuracy. It tracks the strength of the actual aurora, in the sky, in real-time.

An excuse often given is that Kp is used by scientists because they are not interested in aurora but more in damaging effects on power grids and spacecraft. However, this doesn't really hold water because the most intense electrical currents occur at the peak of the auroral substorm, so a system like Glendale App would be much more appropriate.