All about the Kp index

Everything you need to know about the Kp number system
and viewing auroras at lower latitudes

Kp index map Europe

The most important thing to know about aurora watching is the kp index. It is a scale of numbers between 0 – 9 known as the planetary index. Using this scale, it is easy to determine what kp number you need to have a chance of seeing auroras where you are. So look on the map, have a look which line and which corresponding kp number are on top of or just above your location. Remember this number, it will never change (well the magnetic poles are moving slowly each year so you may need to review it again in about 20 years).

Now when you check the aurora forecast page, you will know what kp number to look out for to be in with a chance of auroras where you live.

How the numbers work

The kp number system is just a scale of geomagnetic activity. It is not a plot map where you can definitely say auroras will be visible. But experience tells us where auroras are visible and at what point of the kp scale they were visible at. So we can plot a map and say for example, this place usually gets auroras when Kp6 level is met. And so on and so forth. But it is not exact. So we would recommend if the maps says you need kp6, then go out when it is Kp5, because you might get lucky.

The kp numbers start at 0 and as the geomagnetic (aurora) strength increases, so too does the kp number. So kp 0 being a very weak or none existent aurora, right through to 9 being a major geomagnetic storm with auroras likely in France and even Northern Spain.

Geomagnetic Storms

Geomagnetic storms are labelled G1 to G5. It is a period when there is strong to very strong geomagnetic activity due to a lot of build up in Earth’s magnetotail which causes magnetic reconnection and snap back to occur, this accelerates a lot of particles back towards earth (a natural particle accelerator if you will) which can spark really awesome northern/southern lights displays. As aurora chasers, geomagnetic storms are what we are always hoping for. Here is a table which converts the G into Kp.

G1 = Kp5
G2 = Kp6
G3 = Kp7
G4 = Kp8
G5 = Kp9

About the image

The image above is just a guide and it should be used as such. Nothing is definite with the aurora, (or the kp number system for that matter). We are still in our infancy of aurora predictions, and it will be a long time before we are able to predict them to be on your doorstep. There are only a couple of satellites up there monitoring the solar wind, and only one main one that we get most of our data from. Until we get more satellites up there, and more advanced satellites at that, aurora predictions and the kp scale will be the best system we’ve got.

The lines on the image are where aurora should be visible from, they do not mean the aurora will be directly overhead. It might be very low down on the Northern Horizon. It all depends on how the aurora is behaving on that particular night.

Viewing auroras

For best chances you should find a place with un-obscured views North and away from light pollution. Unless you are very far north, the auroras won’t be overhead like they are in pictures, they will likely be on the northern horizon, so for maximum chances of seeing it, you should find a hill, wide open field, beach etc so you can see the northern horizon.

Try to adapt your eyes to the dark, this will help you see it better. Don’t look at bright things or use a white torch/flashlight, use a red LED headlamp (it seems too dark at first but once your eyes get properly adapted to the dark the red light is enough to see where your walking). Whatever you do, don’t look at a bright phone/table screen it will ruin your night vision you have just taken to long to get good (can take up to 30-60 mins to get your eyes properly dark adapted). Obviously you will need to look at your phone/tablet to see this website and see the northern light info, so put the brightness to the minimum allowed on the device before you leave the house. Quite often the factory minimum brightness is still too bright once your out there and your eyes are properly dark adapted, so you should get an app that makes the screen even darker still. On my google nexus 7 I use an app called night mode and have it on about 20% or 30% brightness. I also turn the dashboard lights down on the car, clip the stereo front off and I won’t use the main beams unless I have to. This can mean you see even the faintest aurora when the person standing next to you looking at bright phone screens and shining a bright torch everywhere can’t see a thing.


Good luck in your aurora chasing – Tony

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