Seeing the Aurora Borealis – or the Aurora Australis – is on a lot of people’s ‘must see’ bucket list. Including mine. These mesmerizing displays of vibrant colors dancing across the night sky have captivated human imagination for centuries, inspiring folklore, mythologies, and scientific inquiry. It’s well known that the Northern and Southern Lights occur around the polar ice caps so if you want to see them you need to head north to Scandinavian parts, Canada, or Russia, or south to places like Tasmania or Patagonia if you don’t want to go as far as Antarctica.
What causes the auroras?
The Sun constantly emits a stream of charged particles, known as the solar wind, into space. These particles, predominantly electrons and protons, travel at incredibly high speeds. The Earth’s magnetic field, stretching from its core into space, acts as a protective shield, deflecting the solar wind away from the planet. However, near the poles, this magnetic shield weakens, allowing some of the charged particles from the solar wind to penetrate into the upper atmosphere.
As these charged particles collide with gases such as oxygen and nitrogen in the Earth’s atmosphere, they impart energy to them. This energy excites the atoms and molecules, causing them to emit light of varying colours. The colours depend on the type of gas excited and the altitude at which the collisions occur. Oxygen atoms typically produce green and red hues, while nitrogen molecules often emit blue and purple shades. The altitude of the auroras varies from about 80 to 300 kilometres above the Earth’s surface, with different altitudes corresponding to different colours.
The intensity and frequency of auroral displays are influenced by solar activity. During periods of heightened solar activity, such as solar storms or solar flares, the Sun releases an increased amount of charged particles into space. When these particles reach the Earth, they can generate more spectacular and widespread auroras, visible at lower latitudes than usual.
Last weekend’s events were unusual. The NOAA Space Weather Prediction Centre reported that the planet experienced an extreme geomagnetic storm (G5 category), the strongest event since Halloween 2003. On average, there are four of these events per every solar cycle.
A solar cycle lasts for 11 years, going through periods of peaks and troughs of solar activity. We’re in a particularly active part of the cycle at the moment. The auroral activity of the weekend comes from a sunspot called AR3664, which is 16 times as wide as Earth. Sunspots create solar flares. The Sun also releases coronal mass ejections (CMEs) – jets of high-speed plasma travelling at incredibly high speeds. On the weekend, Earth was at the right place and the right time for multiple CMEs to hit at once. Three of them merged into a “cannibal CME” because the last one the Sun released was faster than the other two, gobbling them up.
So… quite a few people were able to tick that celestial light show off the bucket list last weekend without having to do much more than go outside.
The internet is littered with photos of the auroras, some good, some not.
Here in Oz being able to see an aurora in Tasmania or southern Victoria is rare enough to cause excitement. But this one was HUGE, with light shows faintly visible in places as far north as Karratha. My great-nephew, Glenn Casey, is an award-winning photographer who lives in Perth, Western Australia which is normally too far north for an aurora to be visible.
When he heard there was a chance of seeing the display, he drove out of the bright city lights into the Wheatbelt east of Perth where the sky would be dark.
Here are the amazing photos he took near Pingelly. Here’s a link to Glenn’s Facebook page. He has taken some stunning photos over the years.
I didn’t see the aurora. But an interesting thought came to mind. Many years ago I read John Wyndham’s novel, The Day of the Triffids. It was also made into a movie. It’s about a scientist who is working with terrifying poisonous plants that can walk around. It was suspected they were genetically engineered but escaped from the laboratory into the wild. Then one night, there’s a spectacular light show in the sky and everybody who could went outside to look. They all went blind, easy victims to murderous plants. Our hero avoided that fate and woke to a dystopian nightmare.
Maybe I read too much science fiction 😊
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