Aurora Coronas: You might have seen or heard the name somewhere without knowing what it is. And no, it’s not a beer. It’s aurora! Here’s all you need to know about what is widely believed to be the best type of aurora that exists.
The aurora is an elusive but mesmerizing natural phenomenon best seen at Earth’s higher latitudes. When the conditions are favorable enough, the lights can be seen further equatorward but the display will likely be closer to the horizon line and less colorful. At best, the show will consist of bright dancing pillars, which still let you contemplate the real height of the aurora- some 500km of altitude! Here is a snapshot of what it would look like. Remember that cameras can gather more light, thus colors, than our eyes can because their shutter may remain open longer. So it may not look like that in real life…
When you travel to higher latitudes, you get closer to the display. Actually you are now right under it! This zone is called the auroral zone and describes a donut-shaped ring around Earth’s north and south poles. That’s where most of the aurora seen on our planet is created. It’s actually rare not to see aurora at all at these latitudes. Just by changing position, the way you will view the aurora tremendously changes from low to high latitudes. When auroral displays are overhead, you get a totally different perspective. You will have a harder time seeing the whole upward extent of the aurora but you will be closer to it. That means that you will more likely see colors with the naked eye. Sometimes when the auroral activity peaks, the aurora becomes very bright, structured and fast: we call it a coronal aurora or corona.
During a sub-storm, the overhead aurora usually goes from a diffuse narrow band to a wider display that covers much of the sky. It tends to ‘dance’ all around you describing a crown, hence the name ‘corona’. Coronal auroras appear as striped drapes moving rather quickly across the sky. When a drape is right over you (at zenith), you get this mind-boggling vortex effect coveted by so many aurora chasers. The base of the aurora (underlined in white in the photo below) is rather close to you (80-100km above) while the top end of the pillars (black arrow heads) are several hundreds of kilometers further up. This makes the pillars appear to be converging towards the zenith and create a crown shape!
Overhead view of a corona with the base (white) and the canopy (black arrows) extending upwards.
Coronas are probably the most astonishing, yet rare auroral phenomenon, and for good reasons. They usually only happen at high latitudes during substorms but sporadically and very elusively. At lower latitudes you need to wait for a major solar event to push the aurora above you. Coronas are so psychedelic that they make the aurora play tricks on your imagination. The part of the aurora that is right at zenith is the most fascinating to watch according to many stargazers. When a corona explodes, the middle rapidly flickers bright green and pinks. The whole structure also seems to sometimes ‘flow’ as the colors replace each other.
Auroral coronas are also quite famous for the general form they take against the night sky. Some people see birds, dragons, angels, butterflies and all other sorts of shapes. Below are some examples that we took during the last aurora season from the aurora borealis observatory on Senja island. From left to right: Phoenix, dragon, butterfly.
Coronas are the ultimate goal for aurora watchers and chasers. They’re the brightest, fastest and most colorful auroras. They typically allow you to see colors with the naked eye! Unfortunately lots of people never get to see them because of their elusive nature. So the best way to experience them is to book a stay with us at the observatory for at least 5 days to maximize your chances. On average, there were approximately 3 big coronas per month and about 5 minor ones. Of course they don’t necessarily happen at regular intervals but by booking about a week with us, you have very good chances.